occasional rough running

First my engine setup:
IO-360 Parallel Valve
Horizontal induction
dual Plasma III ignition

The problem:
Occasionally, my engine will run rough. I mean rough enough to shake the stick and make the horizontal stab visibly vibrate. All engine parameters look good and there is no perceptible loss of power. The first time it happened I started looking for a place to land. By the time I had figured out where to go and started heading there it started running smooth again. This happens almost every time I fly after a warm start. I've tried running the boost pump with no change. I'm mystified. I thought I'd post the question before I start poking around blindly.

Any thoughts?

Cheers,

JB

Any particular segment of the flight???

Take off, climb, cruise, ETC.

LOP or ROP??

Any specific RPM range?

Check the FI flow divider. Take the top off of it and check to see if there is any particles in there. I had one with a little sliver from a fuel hose and it would flat drop a cylinder every once in a while then run fine after landing and doing a run up. Don

Thanks Mike and Don,

The rough running doesn't start until I'm up cruising. It happens at all altitudes. It doesn't matter if I'm running ROP or LOP. Any RPM.

I'll check the flow divider.

jcbarker said:

Thanks Mike and Don,

The rough running doesn't start until I'm up cruising. It happens at all altitudes. It doesn't matter if I'm running ROP or LOP. Any RPM.

I'll check the flow divider.

Click to expand...

I've experienced rough running, so far it has always been cured by moving the mixture knob in just a bit.

A change in temperature from warm to cooler can cause the engine to run rough (too lean).

David-aviator said:

I've experienced rough running, so far it has always been cured by moving the mixture knob in just a bit.

A change in temperature from warm to cooler can cause the engine to run rough (too lean).

Click to expand...

True, and that was my first thought. However, in this case, adjusting the mixture makes no difference.

Not trying to hyjack this thread but it is similiar to my situation yesterday. Return flight, 8500' cruise, leaned ROP with a lower than normal fuel burn , 11 GPH (IO-540 , RV-10). The engine started running rough so I pushed in the mixture a little.No change so I went full rich, still no change. I was looking for the nearest airport and about four minutes later it smoothened out. The #4 EGT rose up 100 degrees or so and cooled down similiar to the other cylinders as the engine smoothened out. I leaned back to 14.5 GPH and the vibration did not return for the remainder of the flight of about one hr. Any ideas what caused this? Moderators , you can move this post to another thread if it is not appropriate here, but I thought they were similiar problems and dialog on both situations would help both of us.
Ron

Ron B. said:

The #4 EGT rose up 100 degrees or so and cooled down similiar to the other cylinders as the engine smoothened out. .
Ron

Click to expand...

Ron, did the CHT happen to go down on cyl #4 at the same time as the EGT went up????

If so, may be a sticking exhaust valve, or a bit of crud holding the valve open.

I had not been monitoring the engine parameters before the rough running took place (more than the usual scan). When I noticed the higher#4 EGT the cylinder temps were all close as usual. I did not notice if #4 Cylinder temp was a lower one. I was looking to see if it was higher and it was not.
Ron

Ron

Do you have a datalog of the engine monitor.

Send it to me by email if you do.

Couple of things in no particular order that have caused rough running in RV10/IO540's

1. Fuel pump temperature causing vapour bubbles, and as these go through the engine will run rough. richer does not always fix it, although the extra fuel flow means the volume of fuel spends less time in the lines and less chance of heating up. Constant battle down here in summer even with the fuel pump cooling shroud. (although we have tried to improve airflow just this week, time will tell).

2. Plugs....many variables but I have seen this time and time again. Folk and in particulare LAME's (A&P's) seem to disregard this critical thing. If massive electrodes, set between 16-18 thou, do not let them get past 22 thou.

3. Inlet Gaskets. Don't ask me how we know Brand new engine installed and at 230 hrs 5 out of 6 gaskets were cracked, some considerably. Go looking for fuel stains around the inlet tubes and the gasket to head interface. Check all bolts/nuts on your inlet and exhaust flanges. You may well have a couple failing.

4. When you see any rough running, before you break out in a terrified sweat, and preferably while LOP turn a mag off and watch it for 10 seconds, note any changes then do the other. Very helpful in finding plugs, wires and maggies that are faulty.

David, I had noticed a fuel stain on the front left cylinder when returning from Oshkosh. I removed the air intake tube and replaced the gasket the day before this flight.I used aviation gasket sealer with the new gasket as re-torquing did not stop the stainning, I know I will regret using this stuff when I have to remove the gasket down the road. I would say this would be cylinder # 2? Number four would be the left side center cylinder ? and I saw no stains. I just Re-torqued all intake bolts and clamps at annual, say 12 flight hrs ago.
Ron

Where there is one there will be more!

Was this a factory Lycoming?


Sorry for thread drift also

No, rebuilt.

Hey guys,
I think this all applies. Your comment about bubbles in the fuel got me thinking. This seems to happen more after a hot start but not always. Also, I'll pay closer attention to the relationship between the EGT and CHT. Typically by EGTs run within 30 degrees lowest to highest. Switching off an ignition is a good idea as well.

If it's a sticking valve does Marvel Mystery Oil work?