Frustrated in So. Indiana with cub

mpriar

Member
I have an international loboy. Great little machine...but
Will not idle. Here is what I have done. Cleaned carb several times, every oriface,every part, all of it, looks new.
New points,condensor,cap, rotor,plugs,set timing. Checked fuel flow, it will run out gallons at full stream, no filter. Put new manifold gasket on. Cleaned air filter. Will start and run fine on 1/2 choke. When choke off, dies at idle, but will run with no choke at higher rpm. Checked compression, 120 at each cylinder. After it dies will start right up with choke.
HELP HELP HELP, GOING CRAZY!!!
 
Have you given the manifold and carb gasket a propane check? Pull the choke out so as to get it only barely running at idle. (not running well, too little choke). Use a unlit propane bottle (with the nozzle unscrewed from the torch handle so it gives out only propane, no air) open the valve on the bottle ao it would be a good flame (not wide open) and use it around the manifold to see if it perks up. if it does, it has a leak at that spot.
Make sure the idle jet screw has not been twisted off in the body. Jim
 
Don't know on that one, but sometimes there's a fine-mesh screen in the fitting where the fuel line goes into the carburetor. Did you check that screen/filter or was your check of fuel flow with fuel coming all the way and through the float valve. Are you 111% sure the carburetor is assembled correctly?
 
I had the same problem with an H carb that I rebuilt. Had it apart three or four times, cleaned and cleaned and it still wouldn't idle. Finally on the last time apart, I took my torch tip cleaner and poked all of the holes I could find and blew it would with compressed air. Then I did the entire process again! That finally fixed it. To really clean a carb you need to pull out all of the jets too. You may think you have it cleaned out, but I bet there is still an air passage that is plugged up.
 
IH carb. or Zenith? If IH carb. run a small wire thru the main jet. It's the small brass bolt on side of carb. Easy for small debri to clog it. Sounds like you are trying all the right things to track it down. I bought a new main jet for my Cub that is slightly larger than the original.
Larry
 
(quoted from post at 06:20:17 12/28/14) IH- have changed out that jet several times in the last two days

Go over to Farmallcub.com if you don't mind. It is a GREAT forum and everyone there just specializes in the Cubs and Loboys. THey will be able to pin point it almost suddenly I bet and they have alot of pictures that might help you in finding the problem that they will post. Sounds like something might be plugged to me, but have you done the throttle/governor adjustment that is requried "everytime" the carburetor is removed? It is outlined in the original IH owners and service manuals.
 
I put a new crankshaft seal in an air cooled engine. That required removing and re-installing the camshaft. With the engine all back together it just would not start. I opened it up again and found that somehow when I put it back together I had the timing marks on the crank/cam gear set off by 7 teeth. I remember checking those timing marks before I buttoned it up, would have bet my left one that the marks were lined up correctly, but they were not! How they ended up wrong, I still don't know! Just sayin'----
 
Running fine on 1/2 choke indicates a plugged passage. Time to go through and either use a fine wire or appropiate sixed drill bit and clean all passages.
 
(quoted from post at 20:46:28 12/28/14) Running fine on 1/2 choke indicates a plugged passage. Time to go through and either use a fine wire or appropiate sixed drill bit and clean all passages.

Is it possible that from previous cleaning it has left the jet passages "warped"?


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If it has an IH carb, there is supposed to be an idle tube that sticks up from the lower half of the carb that frequently gets broken when taking it apart to clean. Is it there, and if so, is the jet in the bottom open? Item 10 in this parts drawing.

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(quoted from post at 18:20:17 12/27/14) IH- have changed out that jet several times in the last two days
Check the intake manifold for cracks. You don't have draw. We had same problem all of the sudden with a 560 good luck
 
I would lean toward the idle jet being plugged or damaged. If venturi was removable and installed upside down the opposite symptom develops. They will idle fine as venturi has no effect at idle because idle ports are above throttle plate. I am not familiar with a cub carburetor but if throttle place was installed backwards it might also close off the idle ports in the throat.
 

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