Engine rougness

jump4way · #1 01-05-2009, 03:54 PM

I'm having a bit of an engine problem and I'm hoping someone here might have some ideas.

The engine was running great for 6 hours of my flight until only a few miles from my home airport. When I throttled back to slow and enter the pattern the engine started running very rough with visible vibrations of the cowl. Adding power helped it to run better but it still tended to sputter. I didn't spend much time troubleshooting in flight since I was so close to home. I just got it on the runway. When I pulled the power out over the runway the engine completely quit.

I was pretty tired from the trip so I let it sit over night and went back out the next day to troubleshoot a bit. I had thought that it might have been a carb ice problem or water in the fuel. I took fuel samples from both tanks and did not find any water. I went out and ran it up for about 10 minutes to make sure there was ample time for any water in the system to move through it and it still ran rough. I ran the engine as lean as I could get it in hopes of cleaning any fouled plugs. The egine would pick up a couple of hundred RPM with a fully leaned mixture and ran better but still a little rough. The airfield is at 1400 ft. Once that I decided that my attempts to clean the system of water and to clean the plugs was not really doing much, I attempted to shut the engine off. Throttle all the way back, mixture all the way back, the engine would continue to run but only barely. The only way I could get it to shut off was to switch the mags off. I tried it again running the engine to about 600 rpm and pulling the mixture and still had the same problem.

I read somewhere on this forum about a mixture idle adjustment screw on the carb that had vibrated out on some others and hoped that I had a similar problem as that seems like an easy fix. No such luck. The screw is firmly in place. When adjusting the mixture lever the mixture arm at the carb does go all the way to the stops.

I haven't pulled the plugs yet to see but I expect they are fouled out. Perhaps I was running the engine a bit too rich for the flight but I'm not sure. The number 3 cylinder was at about 1350 on the egt where as 1 and 2 were about 1160. That seems like quite a spread to me but I'm not sure if any of this contributes to my problem. The only other thing I noticed was my left mag was running a little rough during my runups during the flight. Switching from one mag to the other during my post flight runup did not make any difference on the engine roughness though.

Any ideas?

David-aviator · #2 01-05-2009, 04:02 PM

Picking up "a couple hundred rpm" by leaning is off the chart. The engine is running very rich and I would suspect the carb float has sunk or the seat is leaking very badly.
Only point of reference for me is a Cessna 150 many years ago, that was the problem.

Geico266 · #3 01-05-2009, 04:33 PM

Sounds like it is time to get the carb rebuilt. Not being able to lean it out is the clue for me.

asav8tor · #4 01-05-2009, 04:41 PM

You would get a much better answer with less back and forth if you put out the Joe Friday "Just the facts Ma'am" in the initial post. The reader has to read half way through before they even find out if you have a carb or FI.

Here would be a SAMPLE post that would help you get the answer you want faster:

---------------------------------------------------------------------
acft / engine
---------------------------------------------------------------------

RV-6
AEIO-360B1F (bendix RSA 5)
1000 hrs since factory new, build 1992
2 Mags, 300 hours since inspection, recent SB N/A
8 Massive plugs less than 100 hours
100LL at all times
no recent work on engine, fuel or ignition system
no significant engine history

----------------------------------------------------------------------
problem
----------------------------------------------------------------------

Engine runs rough

----------------------------------------------------------------------
observations / narrative
----------------------------------------------------------------------

During the decent the engine......... blah, blah, blah

rv6rick · #5 01-05-2009, 04:42 PM

I agree with David

. Exact same symptoms as a friends Lycoming powered RV. Turned out to be a stuck needle valve. I removed the carb and disassembled the float/needle valve assy. Fuel line was flushed to the carb inlet into a bucket via the fuel pump from both tanks prior to putting things back together. Reconnected the fuel line and tested the float/needle valve assy. with the fuel pump on prior to reinstalling the bowl. Been running like a top for a couple hundred hours ever since. Total cost was about an hour to remove the cowls, do the above, and reinstall the cowls.

I didn't have any problems reading your post at all

.

Quote:

Originally Posted by David-aviator

Picking up "a couple hundred rpm" by leaning is off the chart. The engine is running very rich and I would suspect the carb float has sunk or the seat is leaking very badly.
Only point of reference for me is a Cessna 150 many years ago, that was the problem.

McFly · #6 01-05-2009, 04:58 PM

I had a similar problem early on in my flight testing. The engine cutoff worked normally in my case though.

After much head scratching it was determined that a tiny bit of trash (fuel lube from the looks of it) became lodged in the idle jet of the carburetor. The debris was about the size of a pin head. Check the finger screen of the carb. If you have trash in there, I think it would warrant taking the carb apart to inspect the idle jet.

I am by no means an expert. This was just my experience. Good luck. Let us know what you find. Good luck.

jump4way · #7 01-05-2009, 05:14 PM

Thanks for the replies. I guess the next step is to pull the carb and take a look at it.

I'll try to post more clearly next time

mahlon_r · #8 01-06-2009, 05:09 AM

If you have a manual push pull type primer, make sure it isn't unlocked or leaking internally. If the float is leaking on the carb, it should leak static with the application of boost pump pressure. So fuel should run out of the carb/ airbox with the boost pump on for a couple of minutes.
Good Luck,
Mahlon
?The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."

noelf · #9 01-06-2009, 06:16 AM

1)...if you suspect water getting to the carb, then the first place to drain would be the gascolator (if one is installed). For water to get to the carb, the gascolator should be "full" of water.

2)...not sure what carb you have, but there was a recent SB on the MS4-5 concerning the float assemblies. It seems that they had a tendency to get "fuel-soaked" which results in an over abundance of fuel in the carb bowl...which allows excess fuel into the engine.

jump4way · #10 01-06-2009, 10:17 AM

Thanks again for the great feedback.

McFly- is it possible to inspect the finger screen of the carb prior to removal? If so, what part would that be?

Noelf- Do you know where I could find more information on the SB on the MS4-5? I tried a brief search but was unable to find more information.

Thanks again.