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undoctor

Joined: 21 Oct 2008
Posts: 212
Location: Bethelhem, PA

Posted: Wed Aug 18, 2010 6:01 am Post subject: 447 analysis

A question for the experts.  I have a 447 on a Kolb FireFly and have 

been unable to get the engine to settle in mid-range RPMs.  If I have 

the throttle set at a certain point the engine runs strong at 5400Rs, 

but when I try to decrease the Rs to about 48-5000, the smallest 

reduction causes the engine to slow to about 4300.



I pulled the plugs after landing yesterday and the front cylinder's plug 

is an even tan color, but the rear plug is the same tan on half of the 

electrode and ceramic cone and sooty black on the other half.  First 

thing that comes to mind is a leaking head gasket, but also wonder if I 

should check the torque on the head bolts first, and has anyone ever 

heard of a spark plug "leak" - either the gasket or the plug itself?



Further info that may or may not be pertinent, my CHT gauges show one 

cylinder in normal heat range and the other is rather chilly.  Checking 

this out a while back I checked the temp of the plugs and the heads with 

a laser thermometer and they were withing a few degrees of each other, 

so I attributed the difference to the gauge or the thermocouple.  But 

maybe it has something to do with the Blackie Carbon lurking on half my 

rear cylinder plug.



Any thought from the experts on the list will be greatly appreciated.



Dave Kulp

Bethlehem, PA



FireFly 11DMK

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Wed Aug 18, 2010 6:49 am Post subject: Re: 447 analysis

 	  undoctor wrote: 	
		  A question for the experts.  I have a 447 on a Kolb FireFly and have 

been unable to get the engine to settle in mid-range RPMs.  If I have 

the throttle set at a certain point the engine runs strong at 5400Rs, 

but when I try to decrease the Rs to about 48-5000, the smallest 

reduction causes the engine to slow to about 4300.



I pulled the plugs after landing yesterday and the front cylinder's plug 

is an even tan color, but the rear plug is the same tan on half of the 

electrode and ceramic cone and sooty black on the other half.  First 

thing that comes to mind is a leaking head gasket, but also wonder if I 

should check the torque on the head bolts first, and has anyone ever 

heard of a spark plug "leak" - either the gasket or the plug itself?



Further info that may or may not be pertinent, my CHT gauges show one 

cylinder in normal heat range and the other is rather chilly.  Checking 

this out a while back I checked the temp of the plugs and the heads with 

a laser thermometer and they were withing a few degrees of each other, 

so I attributed the difference to the gauge or the thermocouple.  But 

maybe it has something to do with the Blackie Carbon lurking on half my 

rear cylinder plug.



Any thought from the experts on the list will be greatly appreciated.



Dave Kulp

Bethlehem, PA



FireFly 11DMK 	




Yeah, both of my 447's did this. My single carb 503 did it also tho to a lesser degree. I think it's just a property of the single carb configuration, but what the exact cause is I couldn't say.



There's not a whole lot you can do about it, really. One thing that seemed to help on my engines was varying the load in the spot where it tended to wander. I.e. add a little pitch (or just fly slower) to load the engine a bit more. This will require opening the throttle a little more which may get it out of that wandering range (that worked on my old 447 equipped trike) and make it settle down. 



I also tried different needle settings on the theory that it was lean in that spot. Raising the needle one notch helped with the hair-trigger throttle on my trike's 447, but it also made it so rich it stumbled and burbled a little bit. That was more objectionable to me than the wandering so I set it back where it was. 



It sounds like your EGT's are actually a little cool in that range which could be either a little rich or too much load (or both). 



The really expensive option is to go with the dual-carb setup, if you can still get the little Bing carbs and manifolds for this. This will completely eliminate the problem (or at least it did on a friend of mine's Starlight/447), but it may be too pricey and difficult to make it worth it.



I just learned to live with it myself, generally by just flying slower and loading the engine a little more when in that particular throttle range....



LS

_________________
LS
Titan II SS

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Wed Aug 18, 2010 3:38 pm Post subject: 447 analysis

David, A little info please. Is this problem a sudden onset or did it happen gradually? Did the engine sit awhile in storage? 

Is there any crud in the carb float bowl. 

Have you checked the carb socket for cracks? How is your prop set? What RPM do you get static? What RPM do you get at WOT in straight and level flight?

Rick Girard



On Wed, Aug 18, 2010 at 9:00 AM, David Kulp <undoctor(at)ptd.net (undoctor(at)ptd.net)> wrote:

  	  Quote: 	
		  --> RotaxEngines-List message posted by: David Kulp <undoctor(at)ptd.net (undoctor(at)ptd.net)>

  

 A question for the experts.  I have a 447 on a Kolb FireFly and have been unable to get the engine to settle in mid-range RPMs.  If I have the throttle set at a certain point the engine runs strong at 5400Rs, but when I try to decrease the Rs to about 48-5000, the smallest reduction causes the engine to slow to about 4300.

  

 I pulled the plugs after landing yesterday and the front cylinder's plug is an even tan color, but the rear plug is the same tan on half of the electrode and ceramic cone and sooty black on the other half.  First thing that comes to mind is a leaking head gasket, but also wonder if I should check the torque on the head bolts first, and has anyone ever heard of a spark plug "leak" - either the gasket or the plug itself?

  

 Further info that may or may not be pertinent, my CHT gauges show one cylinder in normal heat range and the other is rather chilly.  Checking this out a while back I checked the temp of the plugs and the heads with a laser thermometer and they were withing a few degrees of each other, so I attributed the difference to the gauge or the thermocouple.  But maybe it has something to do with the Blackie Carbon lurking on half my rear cylinder plug.

  

 Any thought from the experts on the list will be greatly appreciated.

 

 Dave Kulp

 Bethlehem, PA

 

 FireFly 11DMK

 

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Aug 19, 2010 2:47 am Post subject: Re: 447 analysis

Dave,



The one 447 I've owned had the rpm instability in the mid-range like you described but it did not have the half black spark plug nor a wide difference in EGT nor CHT between the two cylinders. I suspect the RPM instability is characteristic of this engine but know that the half black is not. I would ignore the RPM issue until you've discovered and fixed the cause of the half black plug.

_________________
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Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Thu Aug 19, 2010 4:20 am Post subject: 447 analysis

Thom, RPM instability is not a characteristic of a properly set up 447. I suspect that Dave's trouble is prop loading, i.e., the usual suspect, but without more info I can't say for sure.When I do the break in and set up per the Rotax manual so that the prop is pitched to reach the peak HP area of the engines power curve the engine performs without quirks. On an older engine it's tough to say without more info. If nothing else, making sure the prop is right, assuming a ground adjustable, is cheap, quick, and most often effective.

 



Rick



On Thu, Aug 19, 2010 at 5:47 AM, Thom Riddle <riddletr(at)gmail.com (riddletr(at)gmail.com)> wrote:

 	  Quote: 	
		   --> RotaxEngines-List message posted by: "Thom Riddle" <riddletr(at)gmail.com (riddletr(at)gmail.com)>

 

 Dave,

 

 The one 447 I've owned had the rpm instability in the mid-range like you described but it did not have the half black spark plug nor a wide difference in EGT nor CHT between the two cylinders. I suspect the RPM instability is characteristic of this engine but know that the half black is not. I would ignore the RPM issue until you've discovered and fixed the cause of the half black plug.

  

 --------

 Thom Riddle

 Buffalo, NY (9G0)

 Kolb Slingshot SS-021

 Jabiru 2200A #1574

 Tennessee Prop 64x32

 

 

 The world is round; it has no point.

   - Adrienne E. Gusoff

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=309360#309360

 

 

 

 

 

 

 

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 http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

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-- 

Zulu Delta

Kolb Mk IIIC

582 Gray head

4.00 C gearbox

3 blade WD

Thanks, Homer GBYM



 

  [quote][b]

_________________
The smallest miracle right in front of you is enough to make you happy....

undoctor

Joined: 21 Oct 2008
Posts: 212
Location: Bethelhem, PA

Posted: Thu Aug 19, 2010 5:54 am Post subject: 447 analysis

Thanks to both of you for your contributions, Lucien and Rick.  I've 

messed with the load factor and there are times I can get it to pull 

steady at 48 - 5000, but I seem to be descending (just ordered a digital 

Attitude Indicator which will make it easier than using the VSI)  It's 

encouraging to know that this part of my question seems to be the 

"nature of the beast."  The 50% tan 50% black spark plug has me a bit 

more concerned, though.



To answer your questions, Rick:  The plane sat for pretty close to a 

year from when I bought it, picked it up and got a home for it.  The 

carb bowl is clean and emptied regularly.  The carb socket is supple and 

sound.  The prop is unchanged from when I bought it.  I show 6200 at 60 

MPH climbout, and I've only run it wide open once straight and level and 

I believe it was 6800 Rs (being a multi-million mile 18 wheeler jockey I 

tend to shy away from high RPMs - I even buy motorcycles that are heavy 

on low RPM torque rather than the high horsepower at high RPM 

screamers...  maybe my mindset is part of the unsettled mid-range question).



Hope that info helps your analysis.  I sure appreciate your input - I 

feel so alone up there when I'm concerned there's a problem; you 

probably know why (20 year anniversary of the incident today!!).



Best,



Dave Kulp

Bethlehem, PA



FireFly 11DMK

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Thu Aug 19, 2010 6:46 am Post subject: 447 analysis

Dave, If it were me, the first place I thing I would do is crank in a little more prop pitch. I usually set a 447 for 6000 RPM static when tied down on the ground at WOT. This puts the engine near the top of the HP curve, but not at the peak. Like you, I'm uncomfortable setting up an engine so that it can run close to it's WOT red line RPM (6800 RPM for the 447). Anyway, with the engine set for 6000 RPM static, you'll find that WOT throttle, in flight will be about 6400.

I recommend, since your engine did sit for a year, that you pull the carb and thoroughly inspect the two idle air bypasses at the floor of the throttle bore. Even a tiny amount of fuel that is allowed to congeal in them will throw off the carb throughout it's range. My 582 drove me nuts trying to tune it up after a year layup while I rebuilt systems on the aircraft. Even though I was careful to drain the float bowls and put in preservative oil, a drop of fuel was all it took to close both those passages and nothing helped until I took a fine needle and a can of carb cleaner worked all the crud out of those two little passages. Put the carbs back on, did a carb synch and no problems since.

 In summary, pull the carb check passages, all jets and the needle valve, pay attention to the idle air passages. When you're sure the carb is all clean, reinstall and set static airplane RPM for 6000. IF the problem persists, at least you have the basics set properly to you can begin checking other things. Without this basic setup you can chase your tail until you're nuts and never find the problem. Seen that one enough times to know.

 Good luck.

Rick



On Thu, Aug 19, 2010 at 8:53 AM, David Kulp <undoctor(at)ptd.net (undoctor(at)ptd.net)> wrote:

  	  Quote: 	
		  --> RotaxEngines-List message posted by: David Kulp <undoctor(at)ptd.net (undoctor(at)ptd.net)>

  



  Thanks to both of you for your contributions, Lucien and Rick.  I've messed with the load factor and there are times I can get it to pull steady at 48 - 5000, but I seem to be descending (just ordered a digital Attitude Indicator which will make it easier than using the VSI)  It's encouraging to know that this part of my question seems to be the "nature of the beast."  The 50% tan 50% black spark plug has me a bit more concerned, though.

  

 To answer your questions, Rick:  The plane sat for pretty close to a year from when I bought it, picked it up and got a home for it.  The carb bowl is clean and emptied regularly.  The carb socket is supple and sound.  The prop is unchanged from when I bought it.  I show 6200 at 60 MPH climbout, and I've only run it wide open once straight and level and I believe it was 6800 Rs (being a multi-million mile 18 wheeler jockey I tend to shy away from high RPMs - I even buy motorcycles that are heavy on low RPM torque rather than the high horsepower at high RPM screamers...  maybe my mindset is part of the unsettled mid-range question).

  

 Hope that info helps your analysis.  I sure appreciate your input - I feel so alone up there when I'm concerned there's a problem; you probably know why (20 year anniversary of the incident today!!).

 

 Best,



 

 Dave Kulp

 Bethlehem, PA

 

 FireFly 11DMK

 

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 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

 

 

 

 



	


-- 

Zulu Delta

Kolb Mk IIIC

582 Gray head

4.00 C gearbox

3 blade WD

Thanks, Homer GBYM

 

 

  [quote][b]

_________________
The smallest miracle right in front of you is enough to make you happy....

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Aug 19, 2010 9:08 am Post subject: Re: 447 analysis

Rick,



On my FS w/ 447, I set the static rpm to 5800 which is more pitch than your recommended 6000 and therefore more loading, and still got the rpm instability that Dave described. I set the pitch several times at various static rpms from 5800 to 6200 and points between and it did not affect this characteristic. All it did was change EGTs, which is what I expected. I never did a thorough inspection/cleaning of the carb because....right after I got it just the way I wanted, except for the inability to hold constant rpm below about 5200 in cruise,...  I broke the airplane and sold its remains.

do not archive

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

rparigoris

Joined: 24 Nov 2009
Posts: 796

Posted: Thu Aug 19, 2010 9:44 am Post subject: 447 analysis

Hi Group I never worked or flew with a 447. It however sounds like too lean of a mixture. First thing is to identify the exact position of the throttle when it happens, then identify what part of the carb controls things at that time. May be taper or shape of jet needle or cutaway of slide that is just not right, not just jet needle position. Some needle jets have holes in the side to draw air, could be that too. If easy perhaps you could select the RPM range and richen the mixture to see if it helps out. Easiest is to try enriching circuit, if no change try to squirting some fuel in cab, if no good try restricting intake of carb if you can do it safetly.Just some ideas. I remember making a new jet needle for a single carb Cayuna with a similar problem that helped out quite a bit. Ron Parigoris    [quote][b]

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Thu Aug 19, 2010 9:44 am Post subject: 447 analysis

Thom, with the vagaries of two stroke performance, it could be that all mine were installed on trikes and all were brand new out of the box when I got them so they had no previous abuse. 



Rick



 On Thu, Aug 19, 2010 at 12:08 PM, Thom Riddle <riddletr(at)gmail.com (riddletr(at)gmail.com)> wrote:

 	  Quote: 	
		   --> RotaxEngines-List message posted by: "Thom Riddle" <riddletr(at)gmail.com (riddletr(at)gmail.com)>

 

 Rick,

 

 On my FS w/ 447, I set the static rpm to 5800 which is more pitch than your recommended 6000 and therefore more loading, and still got the rpm instability that Dave described. I set the pitch several times at various static rpms from 5800 to 6200 and points between and it did not affect this characteristic. All it did was change EGTs, which is what I expected. I never did a thorough inspection/cleaning of the carb because....right after I got it just the way I wanted, except for the inability to hold constant rpm below about 5200 in cruise,...  I broke the airplane and sold its remains.

  

 

 do not archive

 

 --------

 Thom Riddle

 Buffalo, NY (9G0)

 Kolb Slingshot SS-021

 Jabiru 2200A #1574

 Tennessee Prop 64x32

 

 

 The world is round; it has no point.

   - Adrienne E. Gusoff

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=309420#309420

 

 

 

 

 

 

 

 ===========

 -List" target="_blank">http://www.matronics.com/Navigator?RotaxEngines-List

 ===========

 http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

 

 

 

 	


-- 

Zulu Delta

Kolb Mk IIIC

582 Gray head

4.00 C gearbox

3 blade WD

Thanks, Homer GBYM



 

  [quote][b]

_________________
The smallest miracle right in front of you is enough to make you happy....

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Thu Aug 19, 2010 10:06 am Post subject: 447 analysis

Ron, All I can tell you is that two strokes are different from other engines. Getting the power loading of the engine correct is the first essential thing to do before you even try and evaluate any condition (short of known bad parts like stuck rings, metal transfer caused by seizure, piston damage through detonation. On new engines I've never had to do a thing more that drop the needles one notch. Chasing jet combinations is a fools errand for the most part. Stock Rotax engines work out of the box if you A: break them in per the Rotax schedule and B: Set the prop for the correct power loading. It is B: that sets two strokes apart from other engines. 



Rick



On Thu, Aug 19, 2010 at 12:42 PM,  <rparigor(at)suffolk.lib.ny.us (rparigor(at)suffolk.lib.ny.us)> wrote:

 	  Quote: 	
		   Hi Group I never worked or flew with a 447. It however sounds like too lean of a mixture. First thing is to identify the exact position of the throttle when it happens, then identify what part of the carb controls things at that time. May be taper or shape of jet needle or cutaway of slide that is just not right, not just jet needle position. Some needle jets have holes in the side to draw air, could be that too. If easy perhaps you could select the RPM range and richen the mixture to see if it helps out. Easiest is to try enriching circuit, if no change try to squirting some fuel in cab, if no good try restricting intake of carb if you can do it safetly.

Just some ideas. I remember making a new jet needle for a single carb Cayuna with a similar problem that helped out quite a bit. Ron Parigoris

     	  Quote: 	
		  



ist" target="_blank">http://www.matronics.com/Navigator?RotaxEngines-List

tp://forums.matronics.com

_blank">http://www.matronics.com/contribution



	




	


-- 

Zulu Delta

Kolb Mk IIIC

582 Gray head

4.00 C gearbox

3 blade WD

Thanks, Homer GBYM

 

 

  [quote][b]

_________________
The smallest miracle right in front of you is enough to make you happy....

rparigoris

Joined: 24 Nov 2009
Posts: 796

Posted: Thu Aug 19, 2010 2:02 pm Post subject: Re: 447 analysis

Rick

I agree that 2 strokes can be quite different than 4 strokes when it comes to carb tuning. For one thing many don't have an exactly flat torque curve where there is less than optimal combustion taking place at a given RPM range. It could be that all the burnt exhaust gasses are not being expelled from the combustion chamber or that some of the fresh charge is blowing right out the exhaust. The type of exhaust affects power band, as does the intake tuning. BTW I have had great success adding a canister to intake to act as a dampener in several cases with this sort of thing that happens. Yamaha called it a tuned intake. What happens on tune of some 2 strokes is that instead of only sucking through carb, there is a pulse that shoots back out carb a little at certain RPMs. This really screws things up. The canister helps even out this shooting back of airflow. This is usual when engine is out of ideal power band where you are getting a nice fresh charge in cylinder. I agree that first and foremost make sure carb is clean and functioning correctly. (You did remove all jets and make absolute sure no carb snot? Also make sure number on jets is as specified by Rotax). It's true that loading can affect this searching mode. On motorcycles, lets take for example a 1972 Kawasaki H2 3 cylinder two stroke. When you are crusing at 55mph there is little load on motor and motor is not quite in efficient part of torque curve. It would do this hunting trick. I made a pilot controllable air jet where I ran the pilot air screw a little rich with fuel for the 55mph cruise, but you could lean it a bit of other times when you were in stop and go mode. Worked great. Anyway if prop is not loading in a specific install, carb adjustment can quite possible resolve. I forget specifics on motor origin of motor with this problem, but if motor was tuned for higher altitude operation and is now operating at a lower altitude, that will cause a leaner mixture. 

I also shoehorned a YTZ250 engine in a YZ 80 frame, took tune of motor from 5 ports and 32mm carb to 7 ports and 42mm flat slide pretty close to motocross tune. Again had problems with light loading hunting and made a reach down when riding airscrew adjustment after getting carb set optimal. Worked great. BTW tuning did in fact include getting optimal taper to jet needle.

Remember that the exhaust system can greatly effect tune of a two stroke. If it is a tuned exhaust almost always to get optimal performance carb needs tweaking if it was originally tuned for only a muffler. Another often overlooked issue is an exhaust system that changes. On motorcycles with high time carbon coats inside. A slick trick is to light carbon on fire with a oxy acetelene torch, then turn off acetelene and only let oxygen into chamber, watch carbon burn out (cherry red patch). A few taps releases this fine brown/tan residue after carbon stops burning. I have had a handful of subtle tuning issues end up being exhaust related. Not only carbon clogging, but damaged expansion chambers can cause change.

Ron Parigoris

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Thu Aug 19, 2010 4:07 pm Post subject: 447 analysis

Yes, the phenomenon of fuel going back up and out the carb, known as fuel stand off, can be a real issue. This problem was the reason for the invention of velocity stacks.  Unlike the exhaust port the intake port has to rely on a vacuum pulse to pull that ejected charge back down the throat of the carb. Similar problem exists at the exhaust port where a reflected wave is needed to stuff the charge back into the combustion chamber when it would just as soon follow the exhaust gas right on out the pipe until the piston closes the exhaust port. One of the reasons Rotax has come to dominate the market for two stroke engines, IMHO, is that they have offered a package that works right out of the box as long as the installer does two things, break the engine in per the table Rotax puts in the installation manual and set the prop for the right loading. It's that simple. The only mod I have ever had to do is drop the needle one notch.

 Look at the Hirth as the counter example. I had one go round with them and that was enough. The customer absolutely swore the distributor set up the jetting in the carb, and I believe him only because further talk revealed him to be an absolute moron about anything mechanical and removed all question of why he wore velcro closure shoes. Of course the distributor disowned the jet settings I found in the carbs and could tell me nothing about the cut and paste exhaust. Of course they do have a 1000 hour TBO, but I don't think that actually includes engine run time.

 Anyway, thanks for writing back. Do you still fly the balloon? That article you sent me was a hit with my EAA chapter.

Rick 



On Thu, Aug 19, 2010 at 5:02 PM, rparigoris <rparigor(at)suffolk.lib.ny.us (rparigor(at)suffolk.lib.ny.us)> wrote:

  	  Quote: 	
		  --> RotaxEngines-List message posted by: "rparigoris" <rparigor(at)suffolk.lib.ny.us (rparigor(at)suffolk.lib.ny.us)>

  

 Rick

 I agree that 2 strokes can be quite different than 4 strokes when it comes to carb tuning. For one thing many don't have an exactly flat torque curve where there is less than optimal combustion taking place at a given RPM range. It could be that all the burnt exhaust gasses are not being expelled from the combustion chamber or that some of the fresh charge is blowing right out the exhaust. The type of exhaust affects power band, as does the intake tuning. BTW I have had great success adding a canister to intake to act as a dampener in several cases with this sort of thing that happens. Yamaha called it a tuned intake. What happens on tune of some 2 strokes is that instead of only sucking through carb, there is a pulse that shoots back out carb a little at certain RPMs. This really screws things up. The canister helps even out this shooting back of airflow. This is usual when engine is out of ideal power band where you are getting a nice fresh charge in cylinder. I agree that!

    first and foremost make sure carb is clean and functioning correctly. (You did remove all jets and make absolute sure no carb snot? Also make sure number on jets is as specified by Rotax). It's true that loading can affect this searching mode. On motorcycles, lets take for example a 1972 Kawasaki H2 3 cylinder two stroke. When you are crusing at 55mph there is little load on motor and motor is not quite in efficient part of torque curve. It would do this hunting trick. I made a pilot controllable air jet where I ran the pilot air screw a little rich with fuel for the 55mph cruise, but you could lean it a bit of other times when you were in stop and go mode. Worked great. Anyway if prop is not loading in a specific install, carb adjustment can quite possible resolve. I forget specifics on motor origin of motor with this problem, but if motor was tuned for higher altitude operation and is now operating at a lower altitude, that will cause a leaner mixture.

  I also shoehorned a YTZ250 engine in a YZ 80 frame, took tune of motor from 5 ports and 32mm carb to 7 ports and 42mm flat slide pretty close to motocross tune. Again had problems with light loading hunting and made a reach down when riding airscrew adjustment after getting carb set optimal. Worked great. BTW tuning did in fact include getting optimal taper to jet needle.

  Remember that the exhaust system can greatly effect tune of a two stroke. If it is a tuned exhaust almost always to get optimal performance carb needs tweaking if it was originally tuned for only a muffler. Another often overlooked issue is an exhaust system that changes. On motorcycles with high time carbon coats inside. A slick trick is to light carbon on fire with a oxy acetelene torch, then turn off acetelene and only let oxygen into chamber, watch carbon burn out (cherry red patch). A few taps releases this fine brown/tan residue after carbon stops burning. I have had a handful of subtle tuning issues end up being exhaust related. Not only carbon clogging, but damaged expansion chambers can cause change.

  Ron Parigoris

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=309466#309466

 

 

 

 

 

 

 

 ===========

 -List" target="_blank">http://www.matronics.com/Navigator?RotaxEngines-List

 ===========

 http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

 

 

 

 	


-- 

Zulu Delta

Kolb Mk IIIC

582 Gray head

4.00 C gearbox

3 blade WD

Thanks, Homer GBYM



 

  [quote][b]

_________________
The smallest miracle right in front of you is enough to make you happy....

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Thu Aug 19, 2010 5:27 pm Post subject: Re: 447 analysis

David,



I think part of your issue is thats you are running too low RPM



447 503 , 582 will run all day at 5800 to 6000 rpm with EGT in a comfortable 

range. They are made to run in this range and WOT at 6500 to 6800  no 

problem.  Stop worrying.



I assume that you have a stock rotax exhaust ?



Dave

http://www.youtube.com/user/kitfoxflyer

Hundreds of videos with 2 stroke Rotax.

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rparigoris

Joined: 24 Nov 2009
Posts: 796

Posted: Fri Aug 20, 2010 1:56 am Post subject: 447 analysis

Hi Rick" Do you still fly the balloon? That article you sent me was a hit with my EAA chapter."I haven't in several years. building a Europa XS, but will drag it out when I am flying the XS.BTW I needed to cut and paste back together the expansion chamber to get it to fit the "Screwball" frame which changed things a little and also installed a sock air filter that changed things a lot. That engine is 73cc and puts out 22HP. After some fiddeling the thing runs great!Ron Parigoris   [quote][b]

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Fri Aug 20, 2010 5:39 am Post subject: Re: 447 analysis

 	  undoctor wrote: 	
		  Thanks to both of you for your contributions, Lucien and Rick.  I've 

messed with the load factor and there are times I can get it to pull 

steady at 48 - 5000, but I seem to be descending (just ordered a digital 

Attitude Indicator which will make it easier than using the VSI)  It's 

encouraging to know that this part of my question seems to be the 

"nature of the beast."  The 50% tan 50% black spark plug has me a bit 

more concerned, though.



	




You probably won't ever be able to get the mixture exactly the same on both cyls when running the single carb. Like I said, the 503 has the same problem when run single-carb, tho to a lesser degree. So it's not really just a problem with the 447.



So the best you can do is identify the lean cylinder and ensure that that one always runs sufficiently rich. Generally, tho, when jetted according to Rotax specs, you're practically always where you need to be with that. So if you find that you have to jet a long ways from the recommended settings for your altitude and temp, then you know you have a problem.



Rick is right tho that the load on the motor is the main treatment. Particularly if you're underpropped the engine will really wander around in that midrange throttle setting, is what I found.  



Finally, and not meaning to be contrary (only want to save you some money and grief), 6000 rpm all the time is really too much. The 2-strokes, especially the 582, aren't like the 912 series which can be run at max power pretty much all the time. They're 2-stroke engines and they work harder than the 4-stroke 912's do. The 447 is generally more forgiving of this than the other two, but for the longest life I'd personally limit the max rpm on a continuous basis to about 5600; 5400 is the "sweet spot" for the 447/503.  6000+ all the time will knock a bit off your TBO as well as use a lot more gas than you really need to burn.



LS

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undoctor

Joined: 21 Oct 2008
Posts: 212
Location: Bethelhem, PA

Posted: Sat Aug 21, 2010 5:32 am Post subject: 447 analysis

[quote][b]  

      this than the other two, but for the longest life I'd personally limit the max

      rpm on a continuous basis to about 5600; 5400 is the "sweet spot" for the 447/503.

      6000+ all the time will knock a bit off your TBO as well as use a lot

      more gas than you really need to burn.



Thank you all so much for lots of input.  Now I can adjust my flying to what's most agreeable to the 447; especially the RPMs and engine loading. 

I guess it stands to reason the place my engine wants to run is between 52-5400 Rs.  That just felt to me like I was abusing it, but I guess not.

The difference in CHT the gauges show isn't a concern, since checking the temp of the plugs and heads with a laser thermometer immediately after

landing shows they're virtually identical.  



But I'd like to determine why one plug has two different burn rates.  I have a thought/question that may shed some light.  Is there a recommended 

order in which to install the spark plug gasket and the ring that sends the CHT to the gauge?  Does the gasket go up against the plug with the ring

between the gasket and head, or does the ring go against the plug with the gasket between the ring and the head?  Maybe this is a source of

an air leak and may be why the gauges show such a difference in CHT.



Again, thanks for the input on the RPM question.  Much appreciated!!



Dave Kulp

Bethlehem, PA



FireFly 11DMK

      

[/b][b]

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Sat Aug 21, 2010 6:56 am Post subject: Re: 447 analysis

David,   52 to 5400 is not a sweet spot and this is why you might be having issues.  I can run a 503 for 600 hour plus with oil injection at 5800 to 6000 rpm with NO teardowns, de carboning etc-  change plugs  100 to 150 hours. 



Rotax exhaust is what tunes your inpulses( timing )  they do not like to run much under 5400 .  Many guys will modify their exhaust to make things fit but really mess up the tuning. 2 " can lose you 10 to 15% HP easy and change the rpm band of where you get HP and torque. 

To each their own but i base mine on thousands of hours behind them and over 30 years in the air.

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Sat Aug 21, 2010 7:48 am Post subject: 447 analysis

Dave, I have to take issue with the ideas presented here about 447 performance. First take a look at the performance graphs found on page 10-3 of the Operations Manual. The idea that it is best to operate the engine as low as 5200 RPM just isn't supported here. Best fuel consumption, maximum horse power, and maximum torque all occur in the 6000 to 6500 RPM range. Then look at page 10-1 Operating Parameters, cruising speed - 6500 RPM.

Now I know there will be lots of comments and I don't claim any kind of expertise, but when I start thinking about doing something different from the Rotax spec's I remember Brian Carpenter's line, "Rotax has a hundred white coated engineers working on these engines for the last 30 years, what chance do you think you have to come up with something they haven't?"

 So, I still say do it as the book says. Just MHO.

Rick



On Sat, Aug 21, 2010 at 8:31 AM, David Kulp <undoctor(at)ptd.net (undoctor(at)ptd.net)> wrote:

  	  Quote: 	
		                        	  Quote: 	
		  [b]  

      this than the other two, but for the longest life I'd personally limit the max

      rpm on a continuous basis to about 5600; 5400 is the "sweet spot" for the 447/503.

      6000+ all the time will knock a bit off your TBO as well as use a lot

      more gas than you really need to burn.



Thank you all so much for lots of input.  Now I can adjust my flying to what's most agreeable to the 447; especially the RPMs and engine loading. 

I guess it stands to reason the place my engine wants to run is between 52-5400 Rs.  That just felt to me like I was abusing it, but I guess not.

The difference in CHT the gauges show isn't a concern, since checking the temp of the plugs and heads with a laser thermometer immediately after

landing shows they're virtually identical.  



But I'd like to determine why one plug has two different burn rates.  I have a thought/question that may shed some light.  Is there a recommended 

order in which to install the spark plug gasket and the ring that sends the CHT to the gauge?  Does the gasket go up against the plug with the ring

between the gasket and head, or does the ring go against the plug with the gasket between the ring and the head?  Maybe this is a source of

an air leak and may be why the gauges show such a difference in CHT.



Again, thanks for the input on the RPM question.  Much appreciated!!



Dave Kulp

Bethlehem, PA



FireFly 11DMK

      

[/b]



ist" target="_blank">http://www.matronics.com/Navigator?RotaxEngines-List

tp://forums.matronics.com

_blank">http://www.matronics.com/contribution



	


	


-- 

Zulu Delta

Kolb Mk IIIC

582 Gray head

4.00 C gearbox

3 blade WD

Thanks, Homer GBYM

 

 

  [quote][b]

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dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Sat Aug 21, 2010 8:09 am Post subject: Re: 447 analysis

Rick.  you are saying pretty well what I am saying. 



Dave

[quote="rickofudall"]Dave, I have to take issue with the ideas presented here about 447 performance. First take a look at the performance graphs found on page 10-3 of the Operations Manual. The idea that it is best to operate the engine as low as 5200 RPM just isn't supported here. Best fuel consumption, maximum horse power, and maximum torque all occur in the 6000 to 6500 RPM range. Then look at page 10-1 Operating Parameters, cruising speed - 6500 RPM.

Now I know there will be lots of comments and I don't claim any kind of expertise, but when I start thinking about doing something different from the Rotax spec's I remember Brian Carpenter's line, "Rotax has a hundred white coated engineers working on these engines for the last 30 years, what chance do you think you have to come up with something they haven't?"

 So, I still say do it as the book says. Just MHO.

Rick



On Sat, Aug 21, 2010 at 8:31 AM, David Kulp <undoctor> wrote:

  	  Quote: 	
		                        	  Quote: 	
		  [b]  

      this than the other two, but for the longest life I'd personally limit the max

      rpm on a continuous basis to about 5600; 5400 is the "sweet spot" for the 447/503.

      6000+ all the time will knock a bit off your TBO as well as use a lot

      more gas than you really need to burn.



Thank you all so much for lots of input.  Now I can adjust my flying to what's most agreeable to the 447; especially the RPMs and engine loading. 

I guess it stands to reason the place my engine wants to run is between 52-5400 Rs.  That just felt to me like I was abusing it, but I guess not.

The difference in CHT the gauges show isn't a concern, since checking the temp of the plugs and heads with a laser thermometer immediately after

landing shows they're virtually identical.  



But I'd like to determine why one plug has two different burn rates.  I have a thought/question that may shed some light.  Is there a recommended 

order in which to install the spark plug gasket and the ring that sends the CHT to the gauge?  Does the gasket go up against the plug with the ring

between the gasket and head, or does the ring go against the plug with the gasket between the ring and the head?  Maybe this is a source of

an air leak and may be why the gauges show such a difference in CHT.



Again, thanks for the input on the RPM question.  Much appreciated!!



Dave Kulp

Bethlehem, PA



FireFly 11DMK

      

[/b]



ist" target="_blank">http://www.matronics.com/Navigator?RotaxEngines-List

tp://forums.matronics.com

_blank">http://www.matronics.com/contribution



	


	


-- 

Zulu Delta

Kolb Mk IIIC

582 Gray head

4.00 C gearbox

3 blade WD

Thanks, Homer GBYM

 

 

   	  Quote: 	
		  [b]

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