[jpowell13]

Has this ever happened to you? Here are my symptoms: I began to notice a moment's hesitation in the engine when I advanced the throttle for takeoff. Then, when I pulled the mixture to shut down the engine, the engine would keep running (barely) until I switched off the ignition switch. Here's what I found:

If you look closely you'll notice that the bolt holding the bowl has started to back out. In fact, all four bolts were loose and a little gap had opened up between the carb and the bowl. (Notice the blue fuel stain on the bowl.)

I put locktite on the bolts, tightened them and resnugged the fingers on the lock washers. The symptoms dissappeared. The carb is a MA-4SPA which was professionaly rebuilt in 2009.

I will be reaching my finger into the air-intake and pressing against the top plate of my filtered air box to see if it moves during each preflight and visually checking those screws whenever the cowl is off. John

 

[artrose]

Same thing happened to me on 150 hr O-320 E2D. Hesitation climbing out. Same fix. 350 hrs now, no issues.

 

[az_gila]

It's an old known problem -

http://msacarbs.com/pdf/SB-17_O 081210.pdf

http://www.lycoming.com/Portals/0/t...Carburetor Throttle Body Screw Inspection.pdf

http://msacarbs.com/pdf/MSA-14.pdf

No good fixes mentioned though.

 

[jpowell13]

Artrose, Mine is an 0-320D2B with a Sensenich FP. About 370 hrs on the plane and rebuilt carb. Did you stay with the finger washers or go with a different locking method for the bolts?

 

[jpowell13]

Fixes

Thanks for the links Gil. I was wondering about getting bolts with drilled heads and wrapping safety wire around the washer fingers and through the hole in the bolt head in a figure 8 pattern so the fingers are held tight against the bolt heads. John

 

[artrose]

I kept the finger washers, but I look closely at everything each time I open the cowl. If the nuts ever back off again my plan is to drill and safety wire.

 

[az_gila]

Thanks for the links Gil. I was wondering about getting bolts with drilled heads and wrapping safety wire around the washer fingers and through the hole in the bolt head in a figure 8 pattern so the fingers are held tight against the bolt heads. John

IIRC one theory was that the gaskets are shrinking in thickness. It might be dependent on the source of the gasket.

 

[N941WR]

Thanks for posting, I didn't realize that could be an issue.

I just checked my carb, ~450 hours since new, and there is no "shrinkage".

By chance, did you see any blue stains in and around your carb?

 

[jpowell13]

Blue stains

Bill, I noticed the loose bolt first, but the blue stains were there and you can see them in the photo.

Gil, Gasket shrinkage seems likely to me since all four bolts were loose on my carburetor bowl.

 

[DanH]

Remove the float bowl. Examine the "legs" of the venturi insert where it is pressed into the carb body, and ensure they are not protruding above the carb body gasket surface. If they are, there will also be clear impressions in the gasket.