1950 Cub.....Racing Carburetor

Wed Dec 19, 2012 10:50 am

Hi,
Recently, I sent my Carburetor out for a rebuild. It was in need of a good cleaning and was developing a slow starting problem and issues which seemed to be associated with the float valve.
It was returned and look real good.
After installing, engine fired right up on what seemed liked the first full revolution, but it wouldn't idle down. Prior to the rebuild, this tractor idled perfect.
I disconnected the throttle governor linkage and even after running the idle set screw out and manually closing the throttle, it still seemed to be racing at what I guessed to be well over 1200 RPM.
The other interesting fact was I couldn't kill the engine by closing the choke.

Thanks in advance and any thoughts or comments would be appreciated.

Mark

Re: 1950 Cub.....Racing Carburetor

Wed Dec 19, 2012 11:09 am

Check to see if the throttle and choke linkage are on the correct carburetor arms. Easy to get mixed up.

Re: 1950 Cub.....Racing Carburetor

Wed Dec 19, 2012 11:23 am

In addition to what Eugene said - the carb to governor linkage should be re-set every time the carburetor is removed and re-installed. Also make sure the choke arm (if correctly connected) is not turning on the choke shaft.

Re: 1950 Cub.....Racing Carburetor

Wed Dec 19, 2012 11:30 am

Thanks for both the suggestions,

I'm sure the choke and throttle arms are correctly connected and will adjust the linkage when I get home on Friday.
But my thoughts regarding the problem are with the carburetor rebuild.
After disconecting both the throttle and choke rods and manually manuevering the throttle plate, I still could not get the tractor to idle down.
Mark

Re: 1950 Cub.....Racing Carburetor

Wed Dec 19, 2012 11:35 am

Either the carb rebuild place forgot to put the throttle and choke plates back in the carburetor, or you have a MAJOR air leak around the intake manifold.

Re: 1950 Cub.....Racing Carburetor

Wed Dec 19, 2012 12:30 pm

The first thing I'd check would be the throttle plate. If it isn't seated correctly and not shutting off the air right, it won't idle down all the way. If the idle screw is backed off all the way and the butterfly closes completely, it has to idle down unless the carb guy accidently drilled something he wasn't supposed to :shock: like a bigger hole in the idle curcuit someplace.
Rick

Re: 1950 Cub.....Racing Carburetor

Wed Dec 19, 2012 1:43 pm

Thanks Rick......I guess I'll need to pull off the carb and take a good look inside

Re: 1950 Cub.....Racing Carburetor

Thu Dec 20, 2012 8:46 pm

Just out of curiosity, where did you send your carb?

Re: 1950 Cub.....Racing Carburetor

Thu Dec 20, 2012 10:07 pm

Hmmmmm...I thought from the post title you put a Weber, Stromberg or big Solex carb on your Cub!

Re: 1950 Cub.....Racing Carburetor

Wed Dec 26, 2012 3:20 pm

Thanks to ll that commented.
After removal, it seemed the throttle plate had be come jammed. Not only jammed, but bent which may have happened by working the hand throttle lever.
Regardless of how it happened, after removing it to straighten, the throttle plate was larger than than the carburetor throat. I took a file to reshape and reduce the diameter.
after reassembly, all is well and the Cub is patiently awaiting the first Northern NJ snow storm to get in some running time.

Again, thanks...Mark

Re: 1950 Cub.....Racing Carburetor

Wed Dec 26, 2012 6:05 pm

Mark, The throttle plate should sit on an angle and the edges are beveled to help it seal when closed. The edge closest to the gas inlet will be further down in the throat if assembled correctly. If you continue to have problems, you may need to replace the plate.

Bob