Carb/Choke Question

Wed Jan 16, 2013 2:35 pm

I have reassembled my cub engine after cleaning the valve guides, laping and adjusting the valves, setting the timing, setting the govenor and throttle linkage and checking all the electrical system. The engine starts on the first turn and runs for 1/2 minute at any rpm and then stalls. I restart it with 1/2 choke and it runs fine until I push the choke rod in. I rebuilt the carb last year and every time I ran the engine I shut the fuel off and ran it out of fuel. It never ran correctly as I had intermittent sticking valves. Several times over the last two years I have chased my tail trying to find various real and IMAGINED engine problems and gave up, leaving the Cub sit for a month or two before starting my search for a remedy again. All along the valves were the problem and I'm at the cusp of finally being ready to push some snow, but the carb/choke problem has me going in circles once again.

The fuel is fresh. The tank is clean. The fuel bowl is clean. Everything appears to be adjusted correctly. :lost: :help: Please

Re: Carb/Choke Question

Wed Jan 16, 2013 2:41 pm

If it runs on half choke and dies on full choke take the metering jet out of the side and run a soft copper wire through it and blow out with carb cleaner. You may have a bit of crud stuck in there. While it is out make sure you get a good, steady flow of gas.


Re: Carb/Choke Question

Wed Jan 16, 2013 2:57 pm

It is most likely a fuel flow issue with it running for 30 sec. before it cuts off. Check to make sure you have good flow coming to the carb. Then work from there. It never hurts to clean the jet. Just sounds more like fuel flow.

Re: Carb/Choke Question

Wed Jan 16, 2013 3:31 pm

And pull the plug on the bottom of the carb and drain out the floaters from there. You can't see floaters of the size it takes to mess up that main jet.

75% of the time when my cub starves for fuel, it's solved by blowing out the jet and draining the bowl. The other 25% of the time, it's out of gas....

Re: Carb/Choke Question

Wed Jan 16, 2013 4:00 pm

ntrenn wrote:The other 25% of the time, it's out of gas....

:lol: :lol: :lol: Been there...Done that!

Re: Carb/Choke Question

Wed Jan 16, 2013 6:01 pm

I did "blow" out the mettering valve but didn't clean it out with a wire. I'll do that in the morning and report back.
Thank you.

Re: Carb/Choke Question

Wed Jan 16, 2013 10:59 pm

ntrenn wrote:........ The other 25% of the time, it's out of gas....
I still consider that a "fuel flow problem" that needs attention and not operator error. :D :lol:

Re: Carb/Choke Question

Thu Jan 17, 2013 9:18 am

Carefully following Barnyard and Boss Hog's advice I removed the metering jet and cleaned it out with a fine copper wire and removed the carb drain plug holding a clean papertowel under it as I took it out. I was amazed a how much very fine crap come out of the carb. The fine wire also found a small piece of a paint chip, I think.

Before reinstalling the plug I opened the fuel shutoff valve to insure that I was getting good flow, which I was.

Reinstalled the metering valve and the plug, opened the fuel shutoff and started it up. Once it warmed up it ran fine without the choke on. Got a little skip so I will recheck the plugs and points.

Just for the record, I did have plenty of fuel in the tank. Sometimes when we think we know what we are doing, the lack of KISS (keep it simple stupid) jumps in and makes us go around in circles.

Thank you for your help once again. Now it's time to put all the sheet metal back on hope for a little snow to push.

Re: Carb/Choke Question

Thu Jan 17, 2013 9:36 am

Clean the inside of the distributor cap, It can get a carbon track that can cause misses. I am glad to see you are another member of the KISS club.