Farmall 300 gas backfire

cuby · Jan 23, 2020

This starts and runs good, but when warmed up & at full throttle it misses, back fires, shoots flames out of muffler, points are set at .020 & good, dist cap is dry and no visual cracks. This is 12 volt with internal resistor in coil. I can ground out each plug and it does make a difference when at idle. No frost at Carb-manifold. Took air cleaner tube loose at carb & makes no difference. This all started when pushing snow.
Any suggestions are helpful. Thanks

caterpillar guy · Jan 23, 2020

You could have several issues going on. Worn distributor,points burned ,condenser,coil and switch, Could all or anyone of them most likely coil or distributor in my mind the advance weights or springs could have been at just the wear point to cause this with the extra work. Bearing in distributor loose causing the points to not stay at the set gap. Coil could be going south. Also if you have a live hydraulic set up it could be a sign of your cam gear getting ready to go south. Just have to check things. Now you have a list to check.

jhncp · Jan 23, 2020

It wouldn't hurt to take sediment bowl off and make sure screen is clean, also blow air back in tank with cock open. Could try turning main jet out a half turn and see if it makes a difference. Possible intake manifold gasket leak?

47fivewindow · Jan 23, 2020

Look at the spark plug wires in the dark. Is fire jumping anywhere? I'm guessing snow melting on the engine started this, so in still suspicious of the dist.cap. Reading others solutions, we sure have had a rash of bad condensers here at YT.

gene bender · Jan 23, 2020

I would use a timing lite go from each plug see if the spark is constant to each plug one at a time that will show if the wire is good and also if the bearing is good in the dist. You can also remove all the plugs after the spark test to see that they are in good condition. When all plugs are out compression check and also check tappets.

rustred · Jan 23, 2020

I would start by doing a compression check and set the valves, may have a tight valve. set the timing then the carb.

warren woodrow · Jan 23, 2020

Happened to me twice . First was worn distributor shaft. Second time was one valve out of adjustment . Hard to believe one valve could cause that but it did .

DeltaRed · Jan 23, 2020

One more thing to consider. Are spark plug wires real wire or carbon/silicone? can make a huge difference.My SuperM did that once(30 years ago). after exhaustive 'trouble shooting',head scratching,cussing?. The issue was the 'wires'.Changed to new real wire plug wires.Hasn't missed a lick since.Prior to then I didn't even know. Thought plug wires were plug wires.

Mac AR · Jan 23, 2020

Were it me, I'd replace the condenser first. It'll cost a whopping 6 bucks at your local parts store and only take a minute to change. Should that not work, check your distributor bolts. Seriously. My 300 did the same thing to me, but worse when I bought it. Ran it for a while then backfired real loud and died. Turns out the distributor bolts loosened off during delivery. So what you might do is check them, and if they seem loose, loosen them up a bit more and start it. Then, slowly turn the distributor until it smooths out. I know it sounds dumb, but it happened to me and that's how I fixed it. Well that, and a new manifold after a particularly bad backfire cracked the old one. Hopefully yours isn't that bad. Good luck and let us know what the culprit is.

Mac

Farmall 300 gas backfire

cuby

Member

caterpillar guy

Well-known Member

jhncp

Member

47fivewindow

Well-known Member

gene bender

Well-known Member

rustred

Well-known Member

warren woodrow

Member

DeltaRed

Well-known Member

Mac AR

Member

Similar threads