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Uneven EGTs at full throttle

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Bill Strahan

Joined: 20 Aug 2008
Posts: 145

Posted: Thu Nov 12, 2009 5:54 pm Post subject: Uneven EGTs at full throttle

Anyone else experiencing very different EGTs at full throttle?  I will see one set of cylinders running 1300-1390 and the other side 980-1050.



2,4,6 are the cold ones.  1,3,5 are the hot ones.  As soon as I throttle back, the EGT drops on the hot side and comes up on the cold side until they're all within about 30 degrees.



This occurs at all altitudes, and is particularly troublesome because I can't run full throttle at altitude.  At 12,500 the hot side is hot as ever, but the cold side is all in the 900s and the engine is pretty rough.  Worst I've seen is just over 1400 on #5 while running 950 on #4.  In that situation, as soon as I pulled the throttle back to about 5 gph #5 dropped to 1370 and #4 came up to 1360!



While it's fun to put along at 4 gph at 12,500 doing close to 140 mph, I'd much rather be able to run it a bit harder...and when I grab the O2 bottle and head the higher altitudes this will become more important.



Anyone else experienced this and fixed it?

catalpaaviation(at)wideba
Guest

Posted: Thu Nov 12, 2009 6:16 pm Post subject: Uneven EGTs at full throttle

Check the inlet manifolds for air leak around the area where the inlets exit

the mix box and that the black joining hose is centre and clamped.



Anthony



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lbmathias(at)verizon.net
Guest

Posted: Thu Nov 12, 2009 7:16 pm Post subject: Uneven EGTs at full throttle

Bill,



    I am having a similar experience; the left side (particularly 4 and 6) 

run in the 1100's during full throttle climb while the right side runs in 

the high 1300's and sometimes over 1400 during climb.   When I reduce power 

in cruise, they get closer but generally run 100-150 degrees difference 

between the two sides.



    I tried an insert in the scat hose connected to the carb but it didn't 

change anything.  I now have a couple fiberglas tubes to insert between scat 

and carb intake.   Haven't been able to get them on yet but hope to soon to 

see if that makes a difference.



    I'll let you know how it turns out.



Linda

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Bill Strahan

Joined: 20 Aug 2008
Posts: 145

Posted: Thu Nov 12, 2009 8:43 pm Post subject: Re: Uneven EGTs at full throttle

 	  catalpaaviation(at)wideba wrote: 	
		  Check the inlet manifolds for air leak around the area where the inlets exit

the mix box and that the black joining hose is centre and clamped.



Anthony



-- 	




Not sure how I'd check for this.  Also, does it make sense that this only happens at full throttle?

catalpaaviation(at)wideba
Guest

Posted: Thu Nov 12, 2009 10:46 pm Post subject: Uneven EGTs at full throttle

Hullo Bill,



To check inlets (by the way this happened to me) take off rubber joiners on

inlets and then try and shift the tube by hand to the intake distributor, if

it moves most likely it is leaking. The tubes have a rubber "O" ring but

sometimes it leaks, they don't always seal, I took the tubes out and cleaned

etc and replaced them using heat resistant silicon, that worked, the one

cylinder that was lean then was the same as the rest.  The other thing you

could try is to check that the inlets where they bolt to the head have

gaskets and they are working.  I have heard that the bolts sometimes are too

long and bottom out before the inlet (or exhaust) pipes are tight.  Check

bolt length by removing one bolt and measuring hole depth.  Yes it would

make sense that at full throttle it would run lean as the engine is working

harder.  The only other thing is, is the air that flows around the cylinders

inhibited in any way as it exits, in other words have you placed a cover

around the fuel pump? If so remove it.



Best of luck



Anthony



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Bill Strahan

Joined: 20 Aug 2008
Posts: 145

Posted: Fri Nov 13, 2009 9:23 pm Post subject: Re: Uneven EGTs at full throttle

I have now read on several different forums how this problem has been fixed by creating a smooth 90 degree transition from airbox to carb instead of the spiral-wrapped scat tubing.



There were many approaches, but the one that sounded the most interesting was the discussion wherein an individual with a Zenair (and I have it on good authority those are the brightest of guys!) related his solution of replacing it with a section from a radiator hose!  I found a second person confirming this was their fix as well.



So today I stopped into my friendly NAPA store and after some convincing that I REALLY did need to just go in the back and climb around to find the right radiator hose I came away with a lower radiator hose from an F-250 Diesel that had 90 degree bends on BOTH ends and appeared to meet the minimum 2.125 ID that I had come up with from a quick check on the plane.



I got it back to the hangar, and set to work on it.  Unfortunately, I cut it just a BIT too short, and was unhappy with it.  It was close, but I wanted it to fit in place even without the hose clamp holding it to make sure there was no tension on it that would cause rapid deterioration.



So I set to work on the other end, and trimmed it in small increments...and cut it too short as well!  I then said "darn" or something quite similar.  



The tube exiting my airbox is pointed forwards slightly, and when I finally got it trimmed enough to fit, when it slid up onto the airbox tube it also slid back and away from the carburetor.



Hmmm.  Another trip to NAPA on the way home and now with two perfect examples of a 1/4" too short piece, tomorrow should result in a working part.  I'll provide pictures and let you know what happens.  The NAPA part number is 9415.  



I did have to stretch the end that goes over the airbox tube slightly, but it's just a nice snug fit on the carb.



My plan is to get it in place, taxi out and make a few aborted takeoffs to get it nice and hot and verify that the RPM on application of full throttle is consistent.  I can't imagine there is a big enough pressure drop to squeeze the hose in any way, since the drop across the air filter has to be tiny, but I'd rather see it in action a few times before I commit to a trip around the pattern.



Should have news tomorrow or Sunday.



Bill

N1BZRich(at)AOL.COM
Guest

Posted: Sat Nov 14, 2009 4:32 am Post subject: Uneven EGTs at full throttle

Bill,

     I suspect you are on the right track.  When  our EAA chapter had similar problems with the Jab 3300 installation in the 601XL  we built, we ended up using a radiator hose from a Caterpillar tractor.   Sorry, don't remember the part number (that was around 2 years ago) but it  solved the problem and continues to work well.

 Blue Skies,

 Buz Rich

  

  

  [quote][b]

Bill Strahan

Joined: 20 Aug 2008
Posts: 145

Posted: Sat Nov 14, 2009 7:50 am Post subject: Re: Uneven EGTs at full throttle

We shall see. Here's the pic of the one I decided wasn't quite good enough.

Bill Strahan

Joined: 20 Aug 2008
Posts: 145

Posted: Sun Nov 15, 2009 6:21 pm Post subject: Re: Uneven EGTs at full throttle

Quick update on the radiator hose experiment.  I got it trimmed and installed, and it looked like a perfectly smooth 90 degree bend.  Ran it on the ground, everything was great, so a re-cowled it and test flew it.



I was quite surprised.  There's a lot going on during takeoff, with vibration from the engine as well as the rolling tires, so it was only after I was airborne that I realized the engine was vibrating pretty hard.



I throttled back slowly, and after pulling the throttle back about 1/2 inch the vibration ceased and the RPMs increaed!



I left it there during climbout, and after reaching a safe altitude I firewalled it again.  Immediate vibration, and drop in EGT on cylinders 2,4,6.  In fact, I was getting higher RPMs with lower fuel flow when it wasn't firewalled.



So, I don't know what to conclude exactly.  Throttled back 1/2-3/4" the engine runs smooth as silk now that I've balanced the prop.  The EGTs all line up within about 30 degrees of each other.  But the closer to firewalled it gets the worse it runs.



At this point, I can conclude that the full throttle problem is not related to the swirl from the SCAT tubing.  That's not to say it isn't related to the 90 degree bend that close to the carburetor, but it seems unlikely.  The problem is actually worse now, since the engine didn't run this rough with the SCAT tubing.



Not sure what to try next, but I'll make a posting if I have a breakthrough.

Clive J

Joined: 03 Nov 2007
Posts: 340
Location: UK

Posted: Sun Nov 15, 2009 11:25 pm Post subject: Uneven EGTs at full throttle

Bill, this is the same as my Esqual though when loaded (lower RPM on

roll and climb out) it's not so noticeable it seems to come in as rpm

increases. 

Something on my to do list when I get the 'other issues' sorted.  



Since I last flew the plane (January 09), I've fitted a smooth bend (GM

engined Vectra from breakers yard) though I didn't expect it to fix

this, just something that has been an improvement for others..

I was more thinking it was about the mixture when off the needle jet and

onto the main jet.



So, thanks for update, I await your next bulletin with interest.



Regards, Clive

Esqual in UK (+ Jab SP)

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Bill Strahan

Joined: 20 Aug 2008
Posts: 145

Posted: Wed Nov 18, 2009 10:23 am Post subject: Re: Uneven EGTs at full throttle

Well, after experimenting quite a bit and flying a couple of hours in different configurations, here's my latest conclusion on my uneven fuel distribution:  I've ordered a Rotec TBI.  



My flight with just the radiator hoes was awful.



After some more research, I tried modifying it with an .025 aluminum insert along the 90 degree bend to stop any rotation and to help it around the corner.  That produced results better than the original SCAT tube but still very uneven.



Then I inserted another short piece of aluminum at 90 degrees to the first to hopefully kill any rotation and get everything lined up before the carb.



Results:  Even better, slightly, but still not acceptable.



I have essentially tried 4 different tube configurations to get the air from the filter box to the carb, and while I have produced varied results, I have not addressed the original problem to my satisfaction.



I spoke with the tech guy at Rotec, who said they had experienced similar problems with the Bing, and while it was a great carb it was very sensitive to slight imbalances and swirl in the flow.  And he assured me their TBI was much less sensitive to those issues.



I'll post under a new thread when I receive and install the Rotec unit.  Fingers are crossed.

info(at)flylightning.net
Guest

Posted: Wed Nov 18, 2009 2:48 pm Post subject: Uneven EGTs at full throttle

Bill,



Sounds like a good tech article on the TBI for the news letter too. I have

drilled 2 more holes in the static tube, the first 1" back from the original

on the opposite side and another 2" rear of the original on the same side.

My TAs and Avg ground speed are now right on. I think Tex was on to

something and the change to your static tube seems to be the same adjustment

N327AL needed. I will try on one of our other Lightnings as this may have to

be added to the build manual.



Nick



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