Running lean after engine work/carb cleaning

This winter I took the head off my '54 Allis B and had the valves done, new valve seals installed and had the head milled back to flat. (there was a 0.004" warp between cylinders 2 and 3. Up to this point the tractor ran flawlessly other than smoking at low rpm. While waiting for the machine shop I ordered a carb kit from YT and cleaned the carb and all the jets. Now, the tractor will run, but not smoothly unless the choke is nearly full on. I can get it to idle smoothly but if I increase the RPM much at all it starts to stumble and run rough. I have replaced the spark plugs on it with both A/C and Autolite and both run the same. I installed a new petcock and fuel line as well but I cannot get the lean condition to clear up. I did remove the idle and "economizer" jets and cleaned them but I took pictures and am 100% certain they went back into the right place. The longer jet was the one I used in the bottom of the float bowl and the shorter one is the idle jet. It is a M-S carb with a non adjustable load jet.

Any ideas would be greatly appreciated as mowing season is rapidly approaching.

Are you sure you have firing order correct? I have run into that problem myself where it will idle ok, but cannot handle any advance of the throttle.

Is the venturi in good condition, did you assemble it into the carb correctly, and is the gasket correct and undamaged and sealing in that area?

Also check the valve tappet setting and any timing changes depending on what you had apart. firing order too.

I regularly run those MS carbs, on my B two C;s, and a CA. When I have had those symptoms after cleaning a carb, it will be when I failed to run a cleaner wire thru the jet passages; and follow that with a shot of carb cleaner. My best tool , on those carbs, is a good set of cutting torch tip cleaners, and compressed air!

I did clean all the jets with guitar strings and do have the venturi in the correct way. I did replace the fuel petcock and fuel line so I will check for good and proper fuel flow at the carb. Yesterday I did some more trouble shooting and found that if I choke the tractor it runs perfectly. So Monday I'll also double check the float level. I did replace the needle and seat and I'll make sure everything is up to snuff there. As far as timing and firing order, before I took the plug wires off I made labels and labeled each plug wire. I did not disturb the distributor or anything there.

It takes a proper fuel air mix to run smooth. The choke shuts off air to get more fuel in the mix. If the jets are clear and the engine has not been modified to require more fuel that the non adjustable power jet will let thru, unless the fuel source is restricted, the engine would seem to be getting air from some source than thru the carburetor intake. I would check all gaskets and shaft seals between the fuel source and the engine head. Ample fuel is first required then enough vacuum to draw the fuel in. If it will run for a long time with the choke on it would seem that the carburetor would have ample fuel in its bowl.

After you have proven that you have ample fuel and the gasket are sealing you have the manifold to check. The manifold could then have an internal leak between the intake and exhaust.

An internal leak I found.

Dick L That one would have never have been found, by me! even if I had suspected an intake leak. What a casting error!

I get a little nuts when gigging into problem and can't sole it quickly. Having bought over a dozen of non running tractors with this engine I have parts on hand. When I didn't find a problem right off and had narrowed it down to the manifold after trying a carburetor from a running tractor I switched manifolds and solved the problem. I figured I wouldn't be able to sleep not understand exactly "WHY". I took the manifold to the band saw and dissected it. It is called core shift. I found core shift in two of the heads on these engines also. I cut into the water jacket on one head while installing valve seat inserts. I found core shift in another head while porting it. Both heads were fine until I started to repair or modify them.

If you put in one of those neopreme needle valves that might be the problem,I've had some problems with them

My old laptop has keys that do not always register when hit. When in a hurry to lay it down I don't always proof read. I hope you can figure out what I was saying. gigging was a mistake by me only and should have been digging. ^D

We all do it one way or another Dick, gin't just you. :wink:

There are two and a half circuits in the carb. The idle circuit, the main circuit and the economizer(half of the main circuit).

If it idles correctly, and the idle mixture can be adjusted from lean, to rich and back, then there's something clogging the main or economizer circuit.

I would go back to the main jet, and remove it, then run the engine, and see what happens. If the main jet is removed, the vacuum draw should make the engine run very rich off idle. It will likely die out without any choke. If you still have to choke it, then there's a clog in the main jet fill port. If it dies because it's running rich, then there's something wrong with the jet.

Similar results with the economizer, but it will happen right off idle, at about 1100 RPM.

If it runs well with the choke on, check the main jet passage again when you have it apart to check the float.

OK, to update everything. Had the carb apart and cleaned and set the float, did this a few times fearing I'd missed something. Took the carb yesterday to an old Allis, International, Dresser, Hough mechanic (he worked for the dealer and started in 1955) He set the float and inspected everything else, handed it to me and said "She should run now."

Brought it home, it still sputters and chugs with anything other than full choke. So I did more troubleshooting. Grounding out plugs 1,2 and 3 made the engine run even rougher. Grounding plug 4 had no effect whatsoever. I swapped plugs in #3 and 4 with the same result. 3 knocked the engine down and 4 had no effect. I was getting fire from the screwdriver to the block on all 4 cylinders but only 1-3 had any effect on the engine running. So I did a compression test thinking I had an internal problem. Of all the cylinders, #4 had the highest compression at 120 lbs with the throttle at idle; the others were between 115-118. My brother and the old mechanic that helped me with the carb, both told me I had a bad distributor cap or a bad plug wire. Went to NAPA today and bought a new cap, rotor and plug wires and installed them all. No change whatsoever to the way the tractor runs. I checked the points and they were dirty so I cleaned and set them to 0.20. Nothing I do seems to have any effect on this engine. For the record, before I fixed it, it ran perfectly other than bad valve seals. I took the head off and had it decked and the valves ground. The only other thing I did was replace the manifold and exhaust pipe with parts I purchased from YT. The manifold fit fine other than it was just slightly thicker than the original and I had to put longer studs in it. If I spray carb cleaner around the intake manifold it doesn't change the characteristics, i.e., I don't suspect the manifold is leaking.

If I can't get this thing straight they may find an Allis B at the river bottom next time they dredge it. :-(

PROBLEM SOLVED!!!!!

I took the manifold I bought from YT off and put the old one back on, rust and all, and it runs fantastic. There must be an obstruction in the exhaust runner on #4. The intake tracts are shared between 1&2 and 3&4 and they look to be clear. I also looked as deep as I could to see if there was an obstruction in the head itself. But with the old manifold the little B purrs like she used to.

Very frustrating, but glad I got it all sorted out.

Good to hear. Thanks for posting your solve, I to have a B and always interested in problems solved.