Farmall Cub

I am having problems with my h. When its first started It runs a little rough but not too bad. Then as it warms up it starts to miss and pop out of the exhaust.
At full throttle the miss is still there but is a little but harder to hear. once warm at idle it misses, pops, and lopes. You can pull the choke out and you can get it to run fairly smooth. It seems to me to be running lean but I am no expert.

I have been working on this for a few days and I am pretty well stumped.

Now for a little backgound, I have had this tractor for about a year and it has always had a very slight miss. I bought it from a guy who said he could never get it to run right so he parked it. I think this miss is what he was talking about.

Two days ago I thought I would change the short piece of pipe coming out of the manifold with a longer one. So with a lot of heat, pounding, and a big pipe wrench I got it out. Now sense I put the new pipe and muffler that miss has gotten a lot worse.

Sense then I have cleaned the carb 3 times, checked the points 2 times, cleaned the cap and rotor, and checked the timing. I even rigged up another small tank that I know is clean.

One other thing, I can unscrew the main jet ( the one on the bottom of the carb) until it almost falls out. But it still does not seem to get to the point of running to rich. unless I use the choke

I am not sure if working on the manifold with the heat and everything may have opened up a crack or hole causing it to run lean. Or if the carb is the problem,maybe spark it has a mag on it, or possibly something else I have not thought of.

So if anyone has an idea let me know. Because I am not sure what to do next.

Thanks for any help
Zack

Run compression test - looking for uneven cylinder compression.
Conduct a vacuum check. This will help isolate the problem area(s).

Mag. Weak or faulty ignition system. Someone didn't reassemble correctly.
Bad spark plug wires.

Just throwing out thoughts.

Possibly a sticking valve. Eugene's suggested diagnostics should tell the story.

I forgot to let you know I checked the compression and I got
1=107
2=110
3=110
4=110
I thought that wasn't too bad

Is there an easy way to tell if the mag is weak or there issome thing wrong with it, this is my first experience with a mag.

Could you give me a quick run down on how to do a vacum test and what to look for?
Thanks for the help so far

You might check the carb. float for a crack. Mine had a very small crack and it caused the fuel level to be off and caused what seemed to sound like a miss.

If you suspect an intake manifold leak use an unlit propane torch and move it around the manifold at all junctions and mating surfaces. If it smooths out you've found your leak.

I put a new float in the carb about two months ago.

I will have to try the propane torch trick tomorrow and see what happens

Since your problem is worse after the engine warms up - run your propane test on a warm engine. You might also consider re-running your compression test after the engine is warm.

I will recheck the compression when it is warmed up.

http://www.performanceprobe.com/index2. ... s/imvt.php

Search vacuum testing automobile - lots of hits telling you hwo to do it and what each reading means.

Thanks for all the help everyone. The problem was a bad intake gasket, I put a new one in last night and it seemed to run great.