Farmall A engine problems

I have a 1940 Farmall A, crank start that is giving me problems. It used to start easily with just a few pulls, but over the past 6 months it has gotten more difficult to start. Many days, I cannot get it to start at all. I replaced the spark plugs about 30 hours ago and that may have helped slightly, but the starting problem has progressed. Another symptom occurs after about 20-30 minutes of use. Initially, there is no missing when the tractor is placed under a mild load, but after the 30 or so minutes, it sounds like all cylinders are not firing when engaging the clutch in 3rd gear. The missing can go away once the tractor is up to speed. There is of course a significant reduction in power when this happens. The missing gets worse the longer the tractor is used to the point where I fear the tractor will stall and then of course not re-start.

Can any of you engine experts give this novice some guidance on where to start looking to identify and then solve the problem. This tractor has served me well over the past 10 years and I want to keep her going.

Doug

The first thing I would do is take a compression check. If you have low compression in one or more cylinders then the engine will have to come apart. If the compression is good and equal, I would look at the Mag, or distributor.

Magneto or battery ignition?

You need to see what your fire looks like at your plugs. Pull off one of the plug wires and hold it about 1/4" away from the plug while someone makes an attempt to start the engine. Don't forget to turn the ignition switch to the on position, if it has a mag the grounding switch needs to be in the run position. If you don't have a hot blue fire from the plug wire your coil is probably weak if you have a distributor. If its a mag it could the coil or the magnets if they're weak on magnetism. Hal

I would be checking the points and cond. before I invested in any coils or magnets.....

An often over looked easy fix is a loose (or internally leaking) intake manifold. As the engine warms up it warps even more and leaks air into the cylinder/s. Check it for snug fastners, and then check with a propane torch (with no nozzle on the torch tip) this extra fuel will make it pick right up when it gets to the leak. (internal leaks to the exhaust can only be found after removal. Jim

Magneto

Thanks to everyone for replying. I finally got some time freed up to try some of the suggests others made. I am happy to report that compression is good (100, 105, 105, 100) – no major rebuild needed. I did look at the spark from this cranked, magneto-started Farmall A. I do not have another magneto-fired tractor to compare. I compared the spark to my 1973 distributor fired Cub. The magneto spark is about ½ as bright as the Cub spark. If others feel this is weak, what should I replace first on the magneto to see if I can improve the spark. As mentioned previously, the plugs probably have less than 30 hrs on them. They still looked very clean. The plug wires also do not have many hours on them, well less than 500 hours I suspect. The magneto cap contacts did seem dull so I attempted to polish them up a bit (no help).

I was unable to check the intake manifold because I cannot get the tractor started again.

One concern I have is that maybe the carburator is where the problem exists. I am losing much more gas out of the bottom of the carburator than I remember happening before (when cranking). This might be due to the fact that previously the tractor started very well. However, I worry maybe I have a stuck float. I did tap multiple times on the carb but no difference. When I pulled the bolt out of the bottom of the carb, there was much gas still in the carb.

What do others think is my next best step?

Thanks again to everyone for their help. Much appreciated.

Doug

Doug,do your self a favor,send your mag to a good and proven repair co.This might seem expensive but its cheaper in the long run.

This advice was bang on. Was not able to shred until tightening those intake bolts up. She ran like a toro after applying that information. I sure did sleep better too.
Thanks,
David