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Farmall h engine troubles

A

Andrew Psencik

Member
Just bought a 42 h. Rebuilt starter and carb. Runs great at about 7/8 choke. Rebuilt the carb thoroughly 3 more times. No change. Started looking for vacuum leaks. Sprayed carb cleaner all over every inch of manifold. It would bog in places, but can"t visually see any cracks. Going to change the gaskets just in case. I also noticed when I removed the manifold someone had replaced it with a Chinese replacement. Any help would be appreciated. Thanks. A.P.
 
put a straight edge across the manifold to see if it is flat. sometimes you can use a double gasket to take up some warping.
 
Bought an new manifold a few yrs back that had a pin hole in it. Tractor wouldn't run right and when I sprayed the manifold found small hole. Cleaned and patched with J.B. weld and took care of problem.
 
Don"t forget the fuel delivery system. Keep in mind the Farmall H tractor has no fuel pump. It depends on gravity to feed gas to the carb. Check for any restrictions in the fuel delivery system. Except for a fuel bowl, there shouldn"t be any filters in the system. They cause too much restriction to flow.
 
I have good fuel flow. Already checked that. Good ignition. Timing set. The tractor runs smooth and has great power when on choke. I suspect a vacuum leak because closing the choke meters the air leaking and incoming from the choke horn to the point where it is close to normal. I do realize that choking pulls more fuel but, I think this perticular issue , the tractor is getting good fuel, but manualy have to adjust the air manually.
 
Open that main jet screw near the bottom of the carburetor as this will enrich the fuel mixture even my garden tractor has that. Hal
 
Here's that main jet screw on a B&S engine. Hal
a92823.jpg
 
Give the ignition system a nthorough check out to be sure it isn't your problem. Should have a good blue spark that will jump 1/4", but I don't think it's your problem. I suspect a problem with your replacement manifold, either a hole or air leak. I would try a known good replacement to see if that fixes the issue.
 
Are you sure you're getting a full flow of gas from the tank to the carburetor? Disconnect the gas line at the carb and hold a clean container to catch the gas. If you have a full stream of gas from the tank remove the tube fitting where your gas line connected and look for a screen. It may be blocked with crud. I would use air pressure and blow out the main jet. Hal
 
You can true up the manifold with some sandpaper and a FLAT surface. If you have thick piece of glass, like a table top, that works great. A welding table is also a good surface if it is clean and smooth.

Use 3M 77 spray adhesive to glue down some sandpaper on your surface. Since a manifold is pretty big you'll either need to find a big piece of sandpaper or use several sheets so you have enough space.

Rub the manifold on the paper in a figure 8 pattern. Keep checking and working until the entire mating surface of the manifold is shined up.
 
Hold your hand over the throat of the carburetor while a helper makes an attempt to start the engine. If there's not much suction usually means low intake manifold vacuum. I would also do a compression check to see what your readings are. Write them down and post them on here. Hal
 
While the tractor is running spray carb cleaner around the manifold and carb and if the engine picks up RPM's then you have a leak and you should be able to isolate it.
 
I had the same problem with a carb I rebuilt on my H. Had to take it apart a second time to clean out a piece of debris in the main jet passage. Ran like a champ afterward. Pull the carb and check all the passages again, especially the main jet. Something is plugged somewhere in there.
 
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