Intermittent stumble at low rpm when engine hot

[petegaz40]

I was having the same issue and had my fuel injectors cleaned and that pretty much cleared it up. 

[Chocks]

On 10/14/2022 at 8:41 PM, Kelpro999 said:

I had the same running condition and found it was slightly bent intake tube clamps at each cylinder intake. The clamps are aluminum and bow around the tube flange & gasket when the fasteners are tightened. The curve is in the machined recess for the tube and easy to miss. Mine was diagnosed at  300hr since lyc factory rebuild.

 

Thank you. I'll check this next. Otherwise, I have exhausted every other possibility I have researched. The "resolution" that I was given for now, was to keep the vacuum pump spooled up to just at 4lbs when it's hot out. That has worked flawlessly thus far.

@carusoam thanks for the heads up on the "" issue. I have corrected that, and hopefully it will help with the search. 

[takair]

4 hours ago, Chocks said:

Thank you. I'll check this next. Otherwise, I have exhausted every other possibility I have researched. The "resolution" that I was given for now, was to keep the vacuum pump spooled up to just at 4lbs when it's hot out. That has worked flawlessly thus far.

@carusoam thanks for the heads up on the "" issue. I have corrected that, and hopefully it will help with the search. 

Here’s an example I found on mine recently when looking for a slightly out of balance EGT.  Temporary fix was a new gasket, but I probably need a long term solution, not sure if that’s machining or new part.  Did not cause the loping you have seen, but perhaps a more extreme case.

[EricJ]

31 minutes ago, takair said:

Here’s an example I found on mine recently when looking for a slightly out of balance EGT.  Temporary fix was a new gasket, but I probably need a long term solution, not sure if that’s machining or new part.  Did not cause the loping you have seen, but perhaps a more extreme case.

The pipe flange can get pinched outside of its groove like that and then it won't seat completely.   When starting to tighten the collar down you can take a screwdriver or a plastic tool between the pipe and collar and wiggle the pipe around until it pops into the groove or seats properly, then torque the fasteners.   You can often tell by visual inspection whether it seated properly, e.g., in your pic above it isn't.    With the collar off and the pipe moved down a bit you can check whether the flange is flat or has been bent.  Cleaning any old gasket material or gunk out of the groove in the collar is a good idea, too.  A pressure check with a shop vac and some bubble solution will show whether it is still leaking or not.

I just did this on my airplane, too, so it's fresh in my mind. 

[jetdriven]

Sometimes those pipes will move even when tightened.  The pipe vibrates and eats up the recess in the collar.  You can sand the collar and restore the pinch fit for the gasket.  Also.  Coat those gaskets in copper spray or aviation sealer.  They aren’t air tight dry.