Carb Issues

[ajhbike]

On my 56 Loboy, it was running fine until I started it today and it would not run without the coke being partially (3/4) pulled out. Push in, it died. Runs sweet with it partially pulled out, but something ain't right. Ideas?

[Barnyard]

Remove and clean the metering jet with a soft copper wire and some carb spray.

[Glen]

Hi,
If it doesn't get fuel to run, the main jet on the carb probably needs cleaning.
It is the hex headed, brass colored part on the lower side of the carb, here is a pic below from TM Tractor, showing where it is. It screws out, take it out and use a small wire in it, like in the pic above, then wash it out, or blow it out with air. Wear your safety goggles when using the air.
Shut off the fuel before removing the main jet, or if you leave it on, you can check the fuel flow there. Catch the fuel in a clean can.
The gasket on the main jet might not seal again if it is old, TM Tractor has new gaskets, here is a listing.

http://www.tmtractor.com/new/fl/4873fp.htm

[ajhbike]

Thanks guys...it worked! And the gasket held. Running like a top.

[ajhbike]

Well, the carb issue is back. So I repeated the cleaning of the fuel jet and removed the fuel line and blew it out just in case there was crud in there. The engine only runs at full choke or it dies. Any other ideas?

[Bob McCarty]

Is the tank clean or is there rust/debris floating around? Is the sediment bowl screen clean?

[Crimson Tim]

Ideas? Yes. How clean is your fuel tank? Any rust or other detritus? Doesn't take much to cause major headaches of the kind you are experiencing.
I would dismantle and clean out the entire fuel line from the tank to the jet again, including the fuel strainer.
There's a how-to on installing a filter on the fuel tank outlet/strainer inlet that may be of interest.
If your tank is rusty, clean it up and coat it with RedKote or POR. I believe there is a how-to on that as well.

Also, make sure you are opening the fuel strainer valve as far as it will go. Open and close stop-to-stop.

Edit: looks like Bob beat me to it.

[Glen]

Hi,
You could do a fuel flow test before taking it apart. Be sure the fuel valve is fully open. Use a clean can that will hold 1 quart or so, and remove the small plug under the carburetor bowl, let the gas run for a minute or so, it should be a good stream, not stopping.

If you looked at everything above the carburetor, and it is clean, and there is a steady flow of gas to the carb, the carb could have one or more passages plugged. You could take it off and take the top off, and clean it out.
Pull the 2 halves straight apart, do not twist them, or you will break the small idle tube, which threads into the top half, and sticks down into the lower half.
Blow out all the passages with air, and be sure they are open. Wear your safety glasses when using the air.

You could check the float height and float drop while it is apart, they have to be set exactly, the specs are in the Cub service manual.
You could check the top half where the bowl gasket goes to see if it is straight, with a straight edge, they warp from tightening the screws too tight, the carb is soft metal.
There is also a screen in the gas inlet, in the carb, by the threads for the pipe. It should be clean. Here is a pic from TM Tractor.

[Barnyard]

Check the choke lever to make sure it didn't flip upside down. This will cause the choke to be open when the lever in pulled out and closed when pushed in.

[Glen]

Hi,
Here is a pic from TM Tractor of where the choke lever, on the carburetor, is usually facing, if the choke rod is the original length.

[ajhbike]

Yes thanks. It must be okay because it was running just fine 2 days prior and I didn't touch the choke rod. I took the fuel line off of the carb and the 4" piece of flex hose that connects it with the upper fuel line from the sediment bowl and blew them out. I will check the sediment bowl and the tank for debris and flow next. If not those, then I suppose I will have to take apart the carb. Bummer...I could have taken it to the Maine Cubfest and gotten it fixed this past weekend.

[staninlowerAL]

I took the fuel line off of the carb and the 4" piece of flex hose that connects it with the upper fuel line ......

If your flex hose connection is old it could be breaking down and small bits of rubber getting into the main jet could be the culprit, it does not take much to plug the main jet. Suggest you replace the line with a new steel one, (5/16 steel brake line works just fine). Check the HOW TO FORUM for some ideas to fab one up or check with TM Tractor for a replacement.

[Waif]

Check the choke lever to make sure it didn't flip upside down. This will cause the choke to be open when the lever in pulled out and closed when pushed in.

That can get confusing from the operators station the first time it happens.
Not unlike figuring out what position the lever is supposed to be in.

My 48 has a choke lever I have not seen in pictures.
It would come loose ,then catch in a different position.
After repositioning it and snugging it up it moved again after a while.

The cast lever had just enough seam left in one area that the tensioning screws head would bind firmly on one side before it was actually seated.
All unseen from my position offside of the carb...

Filed the casting flush and still needed to reduce the screws shoulder diameter a little.
So far, so good.

[ajhbike]

okay, I will check that as well

[ajhbike]

Where exactly is the engine idle adjustment screw on Glen's picture above? I know the lean adjustment is the inclined screw facing the seat,