farmall f20 backfiring

Hi. I have a farmall f20. When I try to start it it starts right up but only runs a idle for 7 seconds mabe. Then it backfires and stops running. It does this over and over. Does anyone have any idea what this could be? The Carb is set like usual.

Are the point clean? Also, could be a condensor. Has this run before? Has anything changed since it last ran? Did it run well the last time? Is the plug wire firing order 1-3-4-2?

Inquiring minds want to know! :wink:

Geeze, I guess you have checked the timing sence your last post. A carb. set to lean will cause backfireing. If it will only idle mabe the carb linkage is not correct. oldiron29

If its backfiring out the carb, it's usually a valve and/or timing issue.

If it's backfiring out the exhaust, it's usually carb or ignition related.

("usually" of course does not mean "always")

Since it runs consistently for 7 seconds, I'd (loosely) rule out valves and timing - if were either of those it should happen immediately)

Assuming it's in the exhaust, it means you're getting unburned fuel exhausted into the exhaust manifold. It may take a little time (7 seconds perhaps) for the exhaust manifold to get hot enough to ignite that unburned fuel.

As counterintuitive as it sounds, that can often happen from the fuel mixture being too lean to burn fully in the cylinder, but it can also happen if it's too rich.

Either way, it's definitely worth playing with the carb.

Another issue could be a cylinder missing, passing unburnt fuel into the exhaust. So check for a good spark on all cylinders, and clean up your points, etc.

Make sure your plugs are clean, and wires are good. Make sure everything is dry.

If still having trouble, adjust your valves and take a closer look at your ignition components.

Essentially, check everything an anything that has to do with getting a proper burn in each cylinder.

Sounds like a fuel flow problem. It runs the carb empty & after it sets it fills slowly to where it runs for 7 seconds again.

Agreed that'd be the most likely cause of it leaning out. Check the gas flow to the carb. If that's fine - you can try giving the carb a few good smacks with something solid (don't go crazy) - sometimes the floats stick, blocking the flow.

If that doesn't do anything, you might have to operate on the carb to see what's going on.

Another quick easy test is to try running it half choked. If it runs ok then, that means you ARE getting enough gas to the carb, but might be running too lean through the carb. Try richening it up a bit before operating.