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engine surging

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kbcarpenter(at)comcast.ne
Guest

Posted: Thu Oct 09, 2008 3:57 pm Post subject: engine surging

I have had a problem of the engine surging.   It began abruptly.  The previous flights were normal.  I am at 500  hours without engine problems.  Now, when I advance the throttle the last  one inch(turbo comes in) the engine starts drops RPM even to the range of  3000.  If I advance the throttle up to about 5500 it runs smoothly, but  beyond that it starts to surge and  will continue varying from 3000 to  4000.  I have ruled out any problem with the Airmaster Prop.  The  surging is too fast for it to be the prop changing pitch.  I talked with  Lockwood and they suggested the carbs need to be overhauled.  They  suggested the fuel pumps might be clogged, but checked that and it runs the same  pressure it has for 500 hours.  The turbo waste gate cycles correctly(I  think)when turning on the master switch and the turbo spins freely.   does the carb need overhauling or cleaning at 500 hours?   Anyone had  this problem?

 Ken Carpenter    N 9XS    Mono 914

   [quote][b]

garrys(at)tampabay.rr.com
Guest

Posted: Thu Oct 09, 2008 4:27 pm Post subject: engine surging

Ken, yes the carbs need cleaning and overhauling on  a regular basis.  My experience with my 914 is about every 300 hours.   You're fortunate you've made it to 500 hours.  I took my plane to Kerry at  Lockwood and he did the overhaul in about 2 hours.  The price was  reasonable and the engine ran beautifully afterward.  What happens is that  the carbs accumulate something they call "snot", which looks like it  sounds.  Causes all sorts of problems.

  

 Best of luck,

  

 Garry Stout

  

 [quote]   ---

paul.the.aviator(at)gmail
Guest

Posted: Thu Oct 09, 2008 5:21 pm Post subject: engine surging

Hi Folks,



Could I offer a contrary view?  I got to 600 hours on my 914 with no

sign off issues wih the carbs, but on the adivce of many I sent my

carbs into Lockwood to have them overhauled.  What a mistake,  the

airplane now uses .3 to .4 more gallons per hour than before and it

took me 4 tries to get the inlet system sealed up again so I could get

maximum boost.



Actually it still is not right, I can only get 27 inches and 16k feet

and I should be able to get 34" so the darn thong is still leaking.



With that said, it may well be your carbs, but the first place I would

go is fuel filters, then look at the fuel pressure (needs to be

measured differentially), then onto the turbo waste gate.  What you

will need to do is disconnect the cable and move it by hand to check

for "stickyness".



After all of the above, yep, I'd mess with the carbs.



Just my 2 cents worth.



Regards,  Paul

budyerly(at)msn.com
Guest

Posted: Fri Oct 10, 2008 2:13 pm Post subject: engine surging

<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]-->  Guys,  Here is my one and a half cents.

  

 When working with Jerry Hope's 914 we found that the reset switch was all  that was necessary to cure the surging...  That is always my first  in-flight correction.  For my older engine, the wiper on the pot in the  turbo servo wore out with time and the servo began to hunt.  By hitting the  reset switch, it momentarily cuts the power and stabilizes the manifold/boost  and the servo related surge/boost fluctuations stop.

  

 As for the carb related problems,  With the engine at idle,  servo locked out (reset switch held to eliminate the servo from operating),  run the engine up until you see about 35-39 inches of MP.  If the engine  does not surge, it is not the carbs.  If you have the dual manometers, and  can watch the MP on each carb, that will tell you volumes about your carb  health.  If one of the altitude compensators is hanging up, the engine will  sag, calling for more boost, then the engine boost clears the carb balance  problem, but that causes a momentary over boost which then causes the servo  to cut boost, which then causes the carbs to be out of balance again.   In this case you will see it in the twin manometers and a carb rebuild kit for  $45 will fix you up.  The carbs on a 914 take about 2 hours to get on and  off, and 1 hour to replace the seals in the carbs.  Then you get to  retune the throttles.  Pay attention to the position of the needle valve  slide clip during the rebuild.  If you get one position off, you will be  running richer or leaner than normal.  Bing has troubleshooting manual on  the web and Rotax has the carb balancing video you can order, so check it  out.  

  

 If your throttle position sensor is worn, that too can cause the computer  to force the engine into a surge on the older slower computer processor.   The program sold by Rotax can check the position sensor.

  

 For low boost, or leaks, wow, that's a new one on me.  I don't get to  fly that high so I have no experience.  My low boost problems is because I  don't set the cable right on the servo or the cable slips.

  

 Rich Schultz found with running on AV Gas, his carbs stayed in tune if he  added just a bit of Marvel Mystery Oil to his gas to lube his carb.  His  problems cleared up.  

  

 Bud

 Custom Flight Creations

(813) 653-4989

 [quote]   ---

kbcarpenter(at)comcast.ne
Guest

Posted: Sun Oct 12, 2008 5:31 pm Post subject: engine surging

I have some follow-up on the surging problem.  Turning off the TCU does not help anything.  In fact, the engine seems to surge and be a little rougher.  I have checked the plugs which were new two hours ago.  The air filter has no effect on the problem.  I have checked the tubing, it is six years old, but looks to be in good condition and no cracks...course you can't see the underside of a lot of the tubing.  The surging varies.  I ran it yesterday and it did not surge at all...manifold pressure up to 38 and it seemed to be cured.  Then today I ran it again and the surging was back.  The surging is over a range from 5000 down to 2000.  Someone was of the opinion that it was almost like the engine was being turned off and as the RPM dropped, being turned back on.  Since the problem occurs only at the higher throttle settings, I had assumed it could not be the electrical system.  The engine does diesel some when t  urned  off.  It has done that for a year or so.  I usually turn off the fuel pumps first and when the pressure drops, then turn off the ignition.  The dieseling is worse if the enginie is hot...like up at 200 degrees or so.  The surging is less severe when the engine is hot...up in the 200 range, and worse with the engine temp at 130.  

 I am leary of the carbs but it sounds like I will have to tackle them if no one comes up with an alternate idea.  No one around Knoxville has experience with a Rotax.  I asked our AI if he knew anything about Rotax engines and he said, "Heck, I can't even spell it!"   The intermittant nature of the surging has added to the frustration.  I can't see anything being done to the engine that makes it behave different.  I have the same gas(half auto high test  and half 100LL) in the plane that was in there when I did two flights before the surging started.  The mag check is normal.  Running both fuel pumps increases the pressure reading but does not change the surging.  It did not surge for 500 hours running on one pump.   Thanks for the ideas thus far.

 Ken Carpenter

 [quote]-------------- Original message -------------- 

From: "ALAN YERLY" <budyerly(at)msn.com> 

   <?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]-->  Guys,  Here is my one and a half cents.

  

 When working with Jerry Hope's 914 we found that the reset switch was all that was necessary to cure the surging...  That is always my first in-flight correction.  For my older engine, the wiper on the pot in the turbo servo wore out with time and the servo began to hunt.  By hitting the reset switch, it momentarily cuts the power and stabilizes the manifold/boost and the servo related surge/boost fluctuations stop.

  

 As for the carb related problems,  With the engine at idle, servo locked out (reset switch held to eliminate the servo from operating), run the engine up until you see about 35-39 inches of MP.  If the engine does not surge, it is not the carbs.  If you have the dual manometers, and can watch the MP on each carb, that will tell you volumes about your carb health.  If one of the altitude compensators is hanging up, the engine will sag, calling for more boost, then the engine boost clears the carb balance problem, but that causes a momentary over boost which then causes the servo to cut boost, which then causes the carbs to be out of balance again.  In this case you will see it in the twin manometers and a carb rebuild kit for $45 will fix you up.  The carbs on a 914 take about 2 hours to get on and off, and 1 hour to replace the seals in the carbs.  Then you get to retune the throttles.  Pay attention to the   posit ion of the needle valve slide clip during the rebuild.  If you get one position off, you will be running richer or leaner than normal.  Bing has troubleshooting manual on the web and Rotax has the carb balancing video you can order, so check it out.  

  

 If your throttle position sensor is worn, that too can cause the computer to force the engine into a surge on the older slower computer processor.  The program sold by Rotax can check the position sensor.

  

 For low boost, or leaks, wow, that's a new one on me.  I don't get to fly that high so I have no experience.  My low boost problems is because I don't set the cable right on the servo or the cable slips.

  

 Rich Schultz found with running on AV Gas, his carbs stayed in tune if he added just a bit of Marvel Mystery Oil to his gas to lube his carb.  His problems cleared up.  

  

 Bud

 Custom Flight Creations

(813) 653-4989

 [quote] ---

rehn(at)rockisland.com
Guest

Posted: Sun Oct 12, 2008 6:52 pm Post subject: Engine surging

Ken  

I attached a section on troubleshooting the carbs.  

This is from a class I took from Rotax on the 900 series engines, I hope it proves useful.  

Jerry

914_trouble_shooting.jpg

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rehn(at)rockisland.com
Guest

Posted: Sun Oct 12, 2008 7:03 pm Post subject: engine surging

Ken  

I sent a troubleshooting idea under separate cover. However I would look for induction leaks at the hoses connecting the carbs to the manifold and the turbo to the air box hose. I replaced my hoses at the carbs with the new Rotax designed hoses and clamps after I had a leak that I couldn’t see. I didn’t have as much of an issue as you but I did have some rough spots that went away with the new hoses and clamps. The trouble shooting idea has an affective method of checking for leaks. Good luck.  

Jerry  

   

        [quote][b]

hervechaussures(at)tiscal
Guest

Posted: Mon Oct 13, 2008 1:25 am Post subject: engine surging

Hi Ken

 I did have the same problem with my 914,and the cause for me was the 2 inches rubber pipe from the cab to the air box to the turbo became loose .check them!!!

 Regards

 Herve G.CHET



 t 02:29 13/10/2008, you wrote:

 [quote]I have some follow-up on the surging problem.  Turning off the TCU does not help anything.  In fact, the engine seems to surge and be a little rougher.  I have checked the plugs which were new two hours ago.  The air filter has no effect on the problem.  I have checked the tubing, it is six years old, but looks to be in good condition and no cracks...course you can't see the underside of a lot of the tubing.  The surging varies.  I ran it yesterday and it did not surge at all...manifold pressure up to 38 and it seemed to be cured.  Then today I ran it again and the surging was back.  The surging is over a range from 5000 down to 2000.  Someone was of the opinion that it was almost like the engine was being turned off and as the RPM dropped, being turned back on.  Since the problem occurs only at the higher throttle settings, I had assumed it could not be the electrical system.  The engine does diesel some when t urned off.  It has done that for a year or so.  I usually turn off the fuel pumps first and when the pressure drops, then turn off the ignition.  The dieseling is worse if the enginie is hot...like up at 200 degrees or so.  The surging is less severe when the engine is hot...up in the 200 range, and worse with the engine temp at 130.  

 I am leary of the carbs but it sounds like I will have to tackle them if no one comes up with an alternate idea.  No one around Knoxville has experience with a Rotax.  I asked our AI if he knew anything about Rotax engines and he said, "Heck, I can't even spell it!"   The intermittant nature of the surging has added to the frustration.  I can't see anything being done to the engine that makes it behave different.  I have the same gas(half auto high test  and half 100LL) in the plane that was in there when I did two flights before the surging started.  The mag check is normal.  Running both fuel pumps increases the pressure reading but does not change the surging.  It did not surge for 500 hours running on one pump.   Thanks for the ideas thus far.

 Ken Carpenter

   -------------- Original message -------------- 

  From: "ALAN YERLY" <budyerly(at)msn.com> 

  Guys,  Here is my one and a half cents.

   

  When working with Jerry Hope's 914 we found that the reset switch was all that was necessary to cure the surging...  That is always my first in-flight correction.  For my older engine, the wiper on the pot in the turbo servo wore out with time and the servo began to hunt.  By hitting the reset switch, it momentarily cuts the power and stabilizes the manifold/boost and the servo related surge/boost fluctuations stop.

   

  As for the carb related problems,  With the engine at idle, servo locked out (reset switch held to eliminate the servo from operating), run the engine up until you see about 35-39 inches of MP.  If the engine does not surge, it is not the carbs.  If you have the dual manometers, and can watch the MP on each carb, that will tell you volumes about your carb health.  If one of the altitude compensators is hanging up, the engine will sag, calling for more boost, then the engine boost clears the carb balance problem, but that causes a momentary over boost which then causes the servo to cut boost, which then causes the carbs to be out of balance again.  In this case you will see it in the twin manometers and a carb rebuild kit for $45 will fix you up.  The carbs on a 914 take about 2 hours to get on and off, and 1 hour to replace the seals in the carbs.  Then you get to retune the throttles.  Pay attention to the posit ion of the needle valve slide clip during the rebuild.  If you get one position off, you will be running richer or leaner than normal.  Bing has troubleshooting manual on the web and Rotax has the carb balancing video you can order, so check it out.  

   

  If your throttle position sensor is worn, that too can cause the computer to force the engine into a surge on the older slower computer processor.  The program sold by Rotax can check the position sensor.

   

  For low boost, or leaks, wow, that's a new one on me.  I don't get to fly that high so I have no experience.  My low boost problems is because I don't set the cable right on the servo or the cable slips.

   

  Rich Schultz found with running on AV Gas, his carbs stayed in tune if he added just a bit of Marvel Mystery Oil to his gas to lube his carb.  His problems cleared up.  

   

  Bud

  Custom Flight Creations

  (813) 653-4989

   ---

darinh

Joined: 20 Apr 2006
Posts: 327
Location: Utah

Posted: Sun Jan 11, 2009 11:09 am Post subject: Re: engine surging

I know this is a fairly old thread but I came across it looking for a solution to a similar problem I am having with my 914.  I am not experiencing the surging to the extent that the original post is but I am seeing rpm of up to 5500 then the last 10% of throttle when the turbo adds full boost, the rpm drop to around 5200 range.  This started happening when the weather started dropping and is getting worse the colder the temps get.  So I originally linked it to jetting.  I have disassemble the carbs and found that both needle clips are in the no. 3 position and SI-914-013 says to put them in no. 2 and SI-914-014 shows the positions as 1 for the 1/3 carb and 2 for the 2/4 carb.  So now I am very confused.  Anyone have better info on where to put the needle clips?

_________________
Darin Hawkes
Series 7
914 Turbo
Kaysville, Utah

hdwysong

Joined: 06 Jun 2008
Posts: 21

Posted: Mon Jan 12, 2009 10:49 am Post subject: engine surging

 	  Quote: 	
		   Anyone have better info on where to put the needle clips?


	


The 914 Heavy Maintenance manual (ed.21/rev.2, 73-00-00 p.2 says to

refer to SI-914-013 or SI-914-015, depending on your airbox part #.



If your airbox part # is 667167 (etched on the aft face of the

airbox), then your jets should be 156 (cyls 1/3) and 158 (cyls 2/4)

and the clips should both be in position 2 per SI-914-015 (pg 3,

paragraph 3.3.2).

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