billinpa

For the 4 cycle guys: I installed a used Magnum 52 in my J-3, fired it up, ran pretty well. Used engine, hasn't run in a few years. When I close the barrel and it runs on and on, put my finger over the carb opening and it stops after about 5 seconds. My 2 cycles stop almost immediately. The high end needle on the 52 seems loose and the O ring feels hard and shrunk on to the needle. Would this be a source of air draw? The low end needle has good resistance. If you all think this is it, I'll get a new needle. I used an accurate digital caliper and the diameter of the ring on the needle is identical to the shaft leading me to believe it has dried out and shrank.
Thanks for any info!

Bill in Pennsylvania

raptureboy

Hi Bill, I had an OS .91 that would run at full speed with the needle completely closed. Turned out the barrel was distorted from having the needle cranked down hard by previous owner. A new carb fixed the problem. By the way are you Bill from TCWS club?

billinpa

Yes, long time TCWS member, at Quakertown now. I went out to the garage an hour later fired it up and it seems that the O ring on the high side needle got wet with fuel, air draw must have sealed and it ran fine. I put my finger over the carb opening and it shut right down. Suspecting the needle ring was dry. Will try again tomorrow. If need be I'll get another needle, seemingly an easy fix. Thanks. Bill

hsukaria

Hi Bill, I have the exact same thing happening with my used ASP 52 4-stroke (same engine as Magnum). The air leak would be at the base of the carb or where the intake manifold meets the cylinder head. The leak in the needle valve actually would only cause fuel to leak OUT, but not air to leak IN because the fuel is coming pressurized from the fuel tank. I will look into new o-ring seals for the carb base and the intake manifold to head connection.

da Rock

O rings are sold in hardware stores. They're also sold by some engine mfgs.

hsukaria

Hobby People sells the o-ring for the carb base (presently out of stock) and the manifold to head gasket (in stock).