Engine misses when throttle is pulled back to set up for landing

RayMadron

I have a 160 HP conversion in a 140 and it has been running fine. It still runs fine when in cruise and take off but when I reduce power for landing it stutters, I increase throttle a little and bring it back and it is ok. I have had it checked out plugs are all clean and gapped ok. Good comprression I'm thinking it is in the carburetor any other ideas before I go back to my A & P?

empannin

1)Can you duplicate it on the ground?

2) When you slowly pull back mixture at idle speed do you get an rpm rise right before it cuts out? (Idle circuit mixture)

3) in the air if you advance or pull back mixture does it change the behavior?

RayMadron

Thanks for the reply I will try what you have mentioned this week. I have tried it on the ground but it doesn't duplicate it.

griff390

https://piperowner.org/talk/discussion/156848/engine-misses-when-throttle-is-pulled-back-to-set-up-for-landing

It has the fingerprint of a fuel delivery problem. It could be that when you pull the throttle back, the plane decelerates and fuel sloshes forward, opening or covering a port or pickup, causing either a rich or lean problem. My guess is your engine is too lean and fuel starved for a couple reasons; A) rich running engines generally chug rather than stumble. B) the plugs from a rich running engine will be covered in black soot, and you already mentioned they were clean.

Adding to Eric's advice: if you pull the throttle back in flight and it stumbles (and the mixture is already full rich), give it a shot of primer. If it smoothes out, it's too lean and starving for fuel.

A too lean condition is caused by either not enough fuel, or too much air. Pulling the throttle back increases intake vacuum, so if your engine has vacuum leaks, this is where they'll show up. Check the intake system for leaks, including the clamps around the rubber sleeves on the intake tubes, and the rubber sleeves themselves (look for cracks or cuts in the rubber). Check intake gaskets at the jug, and base of the carb. Check for anything loose.

Check fuel filters. If the carb hasn't been serviced in a while, it might be time for a carb rebuild. They do wear out, and something as simple as worn bushings around the throttle shaft can cause the symptoms you described.

Just thought of one more thing: check the cap on the gascolator, ensure the gasket is good and is sealing properly.

That's as much as I can think of prior to handing it over to your A&P. Let us know what you find.

RayMadron

I appreciate the info and will let you know what I find out.

planewrench

Ray, as griff noted, induction leak hi potential. I did have a case that acted like that, turned out a cylinder had a broken valve spring.

carl