Allis Chalmers B Barely runs

Levi S

New User
Hello to all, I have a B that will only run at 3/4 throttle and barely runs, it will sputter and sound as if it is missing on one or more cylinders, it has a new manifold, rebuilt mag, carb is rebuilt
(and set to specs from the manual), valves have been adjusted to the proper specs and I am trying to figure out what else it could be, timing was verified and the carb settings should allow for a start
but takes quite a bit of cranking to do so. I've tried leaning it out and richening the fuel mixture and no notable gain in running. I was curious if anyone else has had a similar issue and if so what
should I look at. I pondered on the idea that it could be something to do with the governor but I would prefer to not dive too deep into it if its not a necessity.

Any help is appreciated thank you in advance.
Are you positive the points are opening far enough? My Oliver 1550 had a habit of the arm on the points wearing down so they weren't opening far enough, and it'd act just like that. Like it was starving for gas.
Ill verify points gap tonight, as well as firing order and I purchased a reman mag for it but ill try to replace it with a known good one.
sounds like you firing order is backwards, as that will cause only 2 cylinders to fire.
I bought new plugs yesterday on the way home and was going to go and check the old girl for points gap and timing but the prairie winds persuaded me to stay inside, however I know its not difficult to rebuild the engine and could do it but I'm a bit concerned about the common cracking of the webbing. Is it something that is grounds for looking for a new block or if it looks good it is good?

+1 check firing order. I bought a poor runner and starting from basics realized the prior owner's error. Ran well after that.

New plugs, new plug wires, new distributor/mag cap are pretty good replacements to fix eventual problems anyway. If no change then put the old parts on the backup shelf. Had to pull out the backup starter when a solenoid went bad and took out my newish starter.


Understood, I changed plugs and wires and it runs far better than it did, it will idle but with slight surging but I am concerned that I will have to replace the valves since adjusting the carb and timing on the mag had little affect on run quality and I adjusted the valves prior to startup, however it still sputters a little. also what is a decent oil pressure for these engines, the original gauge did not work so I put one I had lying around on and it holds 20-23 psi.
U missed the compression check. Without that ur in the
dark on the engines condition. Plus youre talking about
replacing valves. Well u need the compression check to
verify that. Plus more to it than just replacing the valves.
Even if u bought new valves they still

Need to be resurfaced along with the seats if they are
good if not they get replaced also. Along with everything
else that goes with the head rebuild. And its not cheap.
Are u sure u set the valves correctly to spec? Think its
.014 on them. Also the carb may need a good soaking
and cleaning as that maybe ur surging. I always wonder
when people say they set the valves , set the points set
the timing there is never a spec they used ???? That is
important info when ur asking for advice. Or how the
carb is set as to how many turns each screw is out.
Mainly the main jet. That is all valuable info.
With these engines I've had the best results with Autolite 295 spark plugs. Also When running a magneto ignition use genuine copper wire core wires, not the modern suppression type plug wires.
I'll add a couple things:
Get a vacuum gage which has the markings on the dial of various conditions. At the very least it ought to idle with a steady vacuum of 17 or more.

Pull the hose from the air cleaner and SEE that the choke plate at the carb inlet operates as it should.
All good suggestions. I was waiting for someone to mention a vacuum check. Sometimes if you spray starting fluid around the manifold with the engine running you can find a vacuum leak. Engine RPM will increase.

I have yet to run a compression test but from cranking it over by hand know the compression is healthy enough for the time being, valves were set to .12 (cold) and points gap to .20, no difference in spraying starting fluid around manifold to check for leaks. I will do a compression test once I get the starter and electrical system replaced. the carb will be rebuilt and be set at 2-3 turns off the seat to start then go from there.

I did the compression test and came out with the following numbers 1=60 2=20 3=60 4=60, after doing this I again checked valve lash and set to 0.010 and no noticeable gain in running, however found a small nest of some sort in what I am assuming is the bypass hole? cleaned everything up and still did not run any better. out of ideas and am probably going to rebuild the engine as it is cheap and easy enough to do and go from there.
Did you try the compression test on Hole No. 2 with a little motor oil pumped through the sparkler plug hole? That could indicate if the leakage was rings, valves, or head gasket.

+1, I replaced WD manifold plus bushings and it runs a lot better. Only replaced the manifold to get the better air flow. Problem was leaky bushings.
leak down test will pinpiont what is leaking in that cylinder tdc on that cyliner will give a percentage of leakage on the intake or exhaust valve or rings

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