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277 keeps falling off the pipe

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Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Tue Apr 09, 2019 5:39 pm Post subject: 277 keeps falling off the pipe

Situation: the Firefly now has a different Rotax 277 on it, 2.58:1 reduction and a 62" two blade Ivoprop. Engine runs great, all the numbers are good, but it won't stay stable on the pipe. 

It will run stabily at 5700 or above, but as soon as you retard the throttle even a little, it slowly reduces the rpm's to 4700 and then stabilizes. Give it a hair of throttle and it begins to slowly increase rpm and stabilizes again back at at 5700.

Years ago I had a Rotax 532 on my MKIII that would do the same thing because it was overpropped with a three blade 64" Ivo. Removed one of the blades and it would then stabilize pretty well at most any rpm.

So the question is this - anyone else have a similar experience with a 2-stroke engine that kept falling off/climbing back up the pipe, and if so, did you cure it by reducing the prop length/prop load? I would like some confirmation/reassurance/feedback before I start shortening the prop.

_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

slingshot003

Joined: 10 Mar 2017
Posts: 28
Location: FL USA

Posted: Wed Apr 10, 2019 6:00 am Post subject: Re: 277 keeps falling off the pipe

Richard,



Is the exhaust a stock 277 exhaust pipe?  If not, an improper taper in the tuned section could be the cause.



Also, adjusting the midrange/full power jetting in your carb might help.  I would theorize that an overly rich mixture in the problematic throttle range could produce those symptoms, but you say the egt numbers are good so that doesn't seem likely.  -Richard Swiderski

Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Wed Apr 10, 2019 1:38 pm Post subject: Re: 277 keeps falling off the pipe

 	  slingshot003 wrote: 	
		  Richard,



Is the exhaust a stock 277 exhaust pipe?  If not, an improper taper in the tuned section could be the cause.  -Richard Swiderski 	


Well, yes and no, I am starting to think no.

The original pipe was a curlyque like the one in the bottom left of the attachment, but we wanted to try something to reduce the engine vibration, and I found a supplier of tapered cones for people who are fabricating their own exhausts and headers. Short version; got a cone that was exactly the right taper and diameter at both the top and bottom when cut to the length as referenced according to the top center pipe in the catalog. At 16 3/4" long, the top diameter where it welds to the can is the same as the diameter of the opening in the can. The diameter at the bottom (small end) is the same as the diameter of the 879-190 female joint connection. 



Consequently I would have bet money that the straight section would be identical to a stock Rotax pipe with that configuration, but I am starting to think it is not.



Flew it twice last night, took a bit of pitch out of the prop each time, trying to compensate for it maybe being overpropped; this chart shows the correct prop diameter and pitch for a 277: http://www.ultralightnews.ca/articles/rotaxproprecommendation.htm

Since we are running a 62" two blade IVO, it seemed possible we are overpropped, However I flew it twice more today each time taking out pitch, to the point that you can't even give it full throttle or it will overspeed, and that was not helpful, so I think I will assume it is not overpropped.

I think I weld the original curleyque pipe back on and see if it runs properly. If that issue gets fixed, then I'll worry about the vibration. 

Or sell it and get a different engine.

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_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

whiskeyvictor36(at)aol.co
Guest

Posted: Thu Apr 18, 2019 8:20 am Post subject: 277 keeps falling off the pipe

I once removed the exhaust system from a Rotax 447, sent it out for refinishing of the exterior.  It was sand blasted and plated with a ceramic product.  When it was returned to me, I could hear what sounded like pieces of sand inside the muffler if it was turned over or shaken.  Tried blowing and vacuuming it out to no avail.  Assembled it onto the 447 and went flying.  I had not changed anything other than the exhaust refinishing.  However, the 447 acted pretty much just like what you described.  It would not hold a steady RPM.  I thought incorrectly that the sand pieces were maybe to blame.  Although the plane had set for several weeks, I assumed the tuning of the carb should still be OK.  BUT, because I didn't really know what else to do, I changed the needle position.  I can't recall which way it was moved (up or down) but the next flight resulted in a proper running engine that would hold the RPM selected.  Maybe the temperature had changed requiring the needle to be re-positioned.  All of this was years ago, I got older and can't recall all the details.

 



 Bill Varnes

 FireStar 447 Rotax

 Audubon NJ

 



 

 In a message dated 4/9/2019 9:39:38 PM Eastern Standard Time, thegreybaron(at)charter.net writes: 



   	  Quote: 	
		  So the question is this - anyone else have a similar experience with a 2-stroke engine that kept falling off/climbing back up the pipe, and if so, did you cure it by reducing the prop length/prop load? I would like some confirmation/reassurance/feedback before I start shortening the prop.

Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Mon Apr 22, 2019 5:27 pm Post subject: Re: 277 keeps falling off the pipe

I think we are back on track, new muffler installation, flew it six times this evening, the vibration is gone. So we are half way home. Also came to the conclusion that the prop is too long and the engine is too loaded down. As long as you keep the Firefly in a shallow descent, the engine does not hunt at all, it stays at a constant throttle setting. Raise the nose and load up the prop and it falls off the pipe.

So now we need to learn what is a good length of prop for a 277 with a 2.58:1 gearbox.

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_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

rickofudall

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

Posted: Mon Apr 22, 2019 7:12 pm Post subject: 277 keeps falling off the pipe

Richard, I've lost the part of this thread where you said what the 277 is propped at now. Can you measure the pitch? I've got a couple of props around here I can loan you if we can get close.



Rick

On Mon, Apr 22, 2019 at 8:29 PM Richard Pike <thegreybaron(at)charter.net (thegreybaron(at)charter.net)> wrote:



 	  Quote: 	
		  --> Kolb-List message posted by: "Richard Pike" <thegreybaron(at)charter.net (thegreybaron(at)charter.net)>

 

 I think we are back on track, new muffler installation, flew it six times this evening, the vibration is gone. So we are half way home. Also came to the conclusion that the prop is too long and the engine is too loaded down. As long as you keep the Firefly in a shallow descent, the engine does not hunt at all, it stays at a constant throttle setting. Raise the nose and load up the prop and it falls off the pipe.

 So now we need to learn what is a good length of prop for a 277 with a 2.58:1 gearbox.

 

 --------

 Richard Pike

 Kolb MKIII N420P (420ldPoops)

 Kolb Firefly Part 103 legal 

 Kingsport, TN 3TN0

 

 Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

 

 

 

 

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

neilsenrm(at)gmail.com
Guest

Posted: Mon Apr 22, 2019 7:59 pm Post subject: 277 keeps falling off the pipe

Richard

Good luck with prop selection it's a pain

Sorry to change the subject but I see a white strip on the back of the Kolb part of the motor mount. What is it.

Rick Neilsen

Redrive VW Powered MKIIIC

On Mon, Apr 22, 2019 at 9:29 PM Richard Pike <thegreybaron(at)charter.net (thegreybaron(at)charter.net)> wrote:



 	  Quote: 	
		  --> Kolb-List message posted by: "Richard Pike" <thegreybaron(at)charter.net (thegreybaron(at)charter.net)>

 

 I think we are back on track, new muffler installation, flew it six times this evening, the vibration is gone. So we are half way home. Also came to the conclusion that the prop is too long and the engine is too loaded down. As long as you keep the Firefly in a shallow descent, the engine does not hunt at all, it stays at a constant throttle setting. Raise the nose and load up the prop and it falls off the pipe.

 So now we need to learn what is a good length of prop for a 277 with a 2.58:1 gearbox.

 

 --------

 Richard Pike

 Kolb MKIII N420P (420ldPoops)

 Kolb Firefly Part 103 legal 

 Kingsport, TN 3TN0

 

 Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=488874#488874

 

 

 

 

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Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Tue Apr 23, 2019 4:07 am Post subject: Re: 277 keeps falling off the pipe

 	  rickofudall wrote: 	
		  Richard, I've lost the part of this thread where you said what the 277 is propped at now. Can you measure the pitch? I've got a couple of props around here I can loan you if we can get close.



Rick 	


That is very generous, thank you. We are using an Ivoprop and the problem is the length. We have tried taking the pitch out and that helps, but in order to make the engine behave, we have to way under pitch it. So we are going to shorten it down as soon as we figure out what length it needs to be.



And to Rick Neilsen: just as an experiment, we got several super bright LED strips and hooked them up to a cheap sequence flasher to see how they worked as strobes. 

https://www.ebay.com/itm/2Pcs-17CM-Universal-COB-LED-Strip-Car-Daytime-Running-Fog-Lamp-DRL-Driving-Strip/223078189539?hash=item33f07f09e3:m:mj_Z4BzKmmoMH7vefuvwlew

You can see them from a couple miles away when it is almost dark, but they are no way as bright as one of Dick Kuntzelman's units. They main thing they have going for them is they were cheap and it was an interesting way to spend an afternoon. OTOH, if there is anyone overtaking me on final, they'll for sure see it!

_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Wed May 08, 2019 9:28 am Post subject: Re: 277 keeps falling off the pipe

IT WORKS!



Over the last couple of weeks we tried taking 2" off the prop length; no improvement. But a 60" prop is still plenty of prop for a 277, so no real harm done.



We were about ready to turn the 277 into a boat anchor, and then something stirred way back in the memory banks - Back in 1983, I had a Maxair Hummer with a 277 on it, and when it was new, the engine ran properly with factory jetting. After several months of flying and getting well broken in, it got wonky. Kind of like this one.



Something we noticed on this engine, you could not get the EGT's above 950 under load. If you went smaller on the needle jet, then it would not accept throttle. If you lowered the jet needle lower than normal, it would not accept throttle. The low and mid range was too lean.



So we took off the intake silencer, took everything back to stock jetting. No improvement. The symptoms were constant: would not run normally between 5200 and 5800. It would run fast, or it would run slow, but not at a usable rpm.



So we decided to go bigger on the low end jets and and then see if it would accept smaller top end jets. Bingo!



Stock jets are a 148 main, a 2.72 needle jet, an 8L2 jet needle in the middle #2 clip position, and a 45 idle jet.



Now running a 145 main jet, a 2.70 needle jet, an 8G2 jet needle with the clip in the bottom #3 position, and a 50 idle jet. Set the Ivoprop so that it turns 5900 on climbout and it runs perfect, EGT stays about 1025, good throttle response.



Finally. And it doesn't vibrate.

_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

Last edited by Richard Pike on Wed May 08, 2019 10:48 am; edited 2 times in total

George Alexander

Joined: 10 Jan 2006
Posts: 245
Location: SW Florida

Posted: Wed May 08, 2019 10:39 am Post subject: Re: 277 keeps falling off the pipe

 	  Richard Pike wrote: 	
		  IT WORKS!



...S  ...N   ...I   ...P



Finally. 	




Flaming enthusiasm, backed up by horse sense and persistence, is the quality that most frequently makes for success. Dale Carnegie

_________________
George Alexander
FS II R503
E-LSA N709FS
http://www.oh2fly.net

stuart(at)harnerfarm.net
Guest

Posted: Wed May 08, 2019 3:27 pm Post subject: 277 keeps falling off the pipe

Awesome troubleshoot and fix. Congratulations on a job well done.



Definitely one for the archives!



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