Clean up that carb

stray · Sep 15, 2010

BobRip said:
Why replace the tamper cap? Now you cannot adjust it. I did not know of this cap when I cleaned mine. I guess I missed something.

To keep me from tampering with it again. LOL

stray · Sep 15, 2010

stray said:
My PT 422 2003 model Robin engine started loping. Pretty bad this time. Any way to make a long story short I found that a plug or cap must had fallen or come out. I had cleaned and took apart and blew out but nothing helped. And then I noticed a port that look cleaner than it should be especially when it was below and outside the air filter. With the engine running and it loping as it was I reached in and put my finger over that exposed port. Low and behold the engine smoothed out and ran like new. Here are some pics to help explain.

Ya it is. On top of some old asbestos gasket material.

SwampmanLA · Oct 2, 2010

After several hours of seat time today moving limestone and sand, I began to smell gas from my 422 with a Robin. Then the thing began to stumble at higher RPMs. I had to finish my work at just above idle. Well after getting it back to the garage and letting it cool down a bit, about two beers worth, I pulled the carb apart again. What I found was the float needle valve was stuck causing gas to flood the carb. I guess that was where the gas smell was coming from. Well that was an easy fix but I did stumble onto a few interesting things doing this.
1. There are five holes around the intake of the carb. These are overflow tubes and when the needle value is stuck gas will pour into your carb even when the engine is shut down and the key off.
2. The fuel shut off solenoid value is downstream from the float needle valve. What this results in is the ability for gas to enter the carb, and the engine through the overflow tubes, with the key off and the needle valve stuck in the open position.
3. Even after cooling for a couple of beers once I had the top off of the carb the gas in the bowl was boiling!
So I guess the moral of this story is that if you don't have a gas shut off valve between your gas tank and engine, you need one!

MuncyBob · Oct 3, 2010

I want to install the fuel shut off valve. Is this something readily available say at a NAPA pats store? I'm guessing it's just a simple on/off valve and all I need to know if the fuel hose inside diameter?

SwampmanLA · Oct 3, 2010

Any auto parts store should have a simple on/off fule valve. Mine was in the small engine section of the store and I think it is 1/4". It is an inline valve so I needed a short piece of hose and clamps to install it.

zman007007 · Oct 3, 2010

Bobrip, next time you"re in a Napa or parts store pick up a small roll of gasket material, make your own gaskets and no more waiting 2 days to get a gasket. They come in diff. thickness's. Just get a roll of about 1/16 thick and one of about 1/8" thick. That should cover about anything. Also tell them you want it for gas. Get the paper type material, and you can make your own. It"s not hard and it doesn"t have to be perfect. They also have material made of cork, if you need it. Pete :thumbsup:

BobRip · Oct 3, 2010

zman007007 said:
Bobrip, next time you"re in a Napa or parts store pick up a small roll of gasket material, make your own gaskets and no more waiting 2 days to get a gasket. They come in diff. thickness's. Just get a roll of about 1/16 thick and one of about 1/8" thick. That should cover about anything. Also tell them you want it for gas. Get the paper type material, and you can make your own. It"s not hard and it doesn"t have to be perfect. They also have material made of cork, if you need it. Pete :thumbsup:

Thanks, good idea.

J_J · Oct 3, 2010

The fuel shut off solenoid was engineered to shut off the fuel in the bowl, so the engine could not draw anymore fuel to the engine after turning the switch off, and to prevent back firing.

Someone makes an electric fuel shut off valve, that would go before the carb. . I have one on an old motor home, and it feeds the gas to the RV generator. A manual valve works just as good, and much cheaper, if you remember to turn it off, and then turn it back on when you next start the PT.

I believe some diesel engines use them also to shut off the engine

MossRoad · Oct 3, 2010

J_J said:
The fuel shut off solenoid was engineered to shut off the fuel in the bowl, so the engine could not draw anymore fuel to the engine after turning the switch off, and to prevent back firing.

Someone makes an electric fuel shut off valve, that would go before the carb. . I have one on an old motor home, and it feeds the gas to the RV generator. A manual valve works just as good, and much cheaper, if you remember to turn it off, and then turn it back on when you next start the PT.

I believe some diesel engines use them also to shut off the engine

My old IH2500b had a fuel shutoff solenoid in the carb bowl of the updraft carb. The carb was lower than about half of the fuel tank. If the shutoff solenoid fails in the open position, it will siphon out the gas tank until the fuel level is lower than the carb. This actually happened to me a couple times. Something about the design of the solenoid made them susceptible to weather. Fortunately, it also had a manual fuel shutoff needle type valve on the side of the fuel filter bowl back under the tank. I always shut that off after use... and many times forgot to turn it back on and died 50 feet down the driveway! :laughing: