Idle cut off issue.

[niss]

I started a facebook page for PA28 140 owners and one of them posted this issue they are having:

i have a brain buster for who ever wants to attempt it.... when i am shuting down i have to move to 1800-2000 rpm then lean out the mixture before she wants to sleep? any answer to that or is that just a piper thing? if you try to lean out at 1000 it just drops and fluctuates from 50-800 and wont cut out

i have all new mags and wiring harness' and mag tests check out at start up and shut down checks

My first thought is this:

My guess would be the mixture control isn't set properly. my thought process being that at low throttle with lean mix your air to fuel ratio is still good enough to sustain combustion, but with a wider open throttle allowing more air and you lean it out the ratio is off.

Am I off the mark?

[really green]

You are on the right track. Seen this snag a few times. Not 100% sure with that engine, however, last time I had that snag on a TIO540, it was internal seals in the throttle servo. Letting fuel to leak past the ICO position. Servo swapped, problem solved. I assume it's a O-320 you're talking about. I would start @ the carb looking for internal fuel leaks. But don't quote me on that, as I havn't touched a carb since college.

[HS-748 2A]

Either your 'idle mixture' is waaay out of whack or your mixture control linkage is falling upart.

You are right about opening the throttle providing a lean enough mixture to finally kill the engine but that is not a good scenario at all.

Do not operate this thing until you get it looked at properly.

'48

Edited to say: I'm sure the above poster has a valid consideration too.

[Jungle Jim]

Niss,

It's the linkage or something inside the carb. It's telling you something. I would have it looked at before flying.

Jim

[niss]

Thanks for the info guys.

Again this is not my aircraft but someone on the facebook page posted this dilema. I forwarded the response off to him.

Thanks!

PS Jim, when you bringing the Thorpe back to NA3?

[Jungle Jim]

Niss,

I am hoping to make the move the last weekend of the month.

Jim

[Old Dog Flying]

I've had problems with my 0235 C2C HC...180 SMOH...remanufactured MS carb MP3SPA. The internal leak was as the result of a missing gasket in the accelerator pump check valve. In addition the float was not that required by the AD and it was rubbing on the inside of the bowl.

The American company that overhauled the carb is no longer in the carb business; I wonder why.

Barney