Farmall Cub compression

[28plymouthman]

Hi All, bought this Farmall cub after sitting under trees for a couple years. 1950. New 6v battery and rebuilt magneto. It has spark to the plugs.
Compression is 100 on 3 cylinders and 70 on one. It tries to start. Put new non IH carburetor on it from ebay. It won;t fire up. Timing is top dead center on pointer and dist rotor is pointing to #1. I already rotated the mag 180 but it only backfires. so I put the mag back. I did pull the head off to unstick 1 intake valve and 1 exhaust valve. Did not pull the valves to grind them. This is my 3rd cub I own. Never had a problem getting one to run before. Need some ideas on this. Any help is appreciated. Thanks.

[ScottyD'sdad]

Try tow starting it. Sometimes, after 1 tow start, it starts normally. Don't know why, but it happens.
Ed

[Don McCombs]

Adjust the float to spec on the Chinese carburetor.

[Glen]

Hi,
Check the spark while the engine is turning over. It should have a strong blue spark, that will jump 1/4", to a bare place on the engine.
A yellow spark is weak, and needs improving.

[tst]

100 lbs is enough to run, backfire could be flooded or timing is wrong, wrong firing order, should be 1342 clockwise, points on a mag should be set at .013

[k hutchins]

I agree with checking fuel flow first. Pull the plug on the bottom of the carb. If that's good, the check the float as previously mentioned. I had one that was set so low it hit the bottom of the bowl and closed the needle valve.

[Crimson Tim]

If it’s been sitting, prime the oil pump!

Rings probably stuck. Put a little seafoam in each cylinder and let sit a couple days. Rotate the engine a quarter turn or so by hand a bit every now and then.

[Shadow_storm56]

I literally had a cub that sat for years and all the valves were stuck, i filled the cylinders with transmission fluid and let it sit for a day. All but 1 cylinder was find then, wouldn't run, took the plug out of the 1 cylinder and it ran on 3. Eventually got the others unstuck and it runs great now but mt point is if you have 1 stuck intake valve it will not run as it blows air back out the carb. If you take out the little plug above the carb and feel air pulsing out when you roll it over then your valve or valves are stuck. Also if the intake losens up but the exhaust is still stuck open it sounds like a really cool motorcycle! I also had to rebuild my carb as it was super gummy but if it backfires it makes me wonder if it's not the valves

[28plymouthman]

Thanks for all the replies. Spark is good. Timing I think is right on. Magneto is .13 at the points. All the valves now move up and down after putting oil in the spark plug holes and letting it set for a couple days. This carb my be the problem. I have a makeshift copper line with a funnel to pour the gas into while I crank it over. By any chance , does the hood have to be on to create more pressure from a couple gallons of gas pushing down the fuel line to the carb for it to start. Will try it today again to see if it will pop. I might try pulling it down the road. You shouldn't have to do that to get it to run.

[Rick Spivey]

By any chance , does the hood have to be on to create more pressure from a couple gallons of gas pushing down the fuel line to the carb for it to start. Will try it today again to see if it will pop. I might try pulling it down the road. You shouldn't have to do that to get it to run.

No the hood does not have to be on. Many of us use a "pony" tank made from a lawn mower, etc. when working on one of these. As for pull starting, I don't disagree with your sentiment that it shouldn't be necessary, but sometimes it is. You'll just have to trust us on that.

[Eugene]

Magneto. Impulse coupling working? Does the magneto click when you crank over the engine? No, impulse coupling not working.

[tmays]

By any chance , does the hood have to be on to create more pressure from a couple gallons of gas pushing down the fuel line to the carb for it to start. Will try it today again to see if it will pop. I might try pulling it down the road. You shouldn't have to do that to get it to run.

As for pull starting, I don't disagree with your sentiment that it shouldn't be necessary, but sometimes it is. You'll just have to trust us on that.

[tmays]

Trust us is right. Granted, in theory you shouldn’t have to pull it off. But I can’t tell you the number of times I’ve seen a tractor being tried and tried with a starter and it not start. Pull it off to start it and from then on it fire right up with the starter. If it won’t start by pulling it, then it definitely wouldn’t have started with the starter

[28plymouthman]

Thanks for the replies again. Haven't tried it lately. So I will leave the hood off and use the small tank. I will try pulling it down the road to get it to start. I remember doing that with my dad on an old car way back. I assume you use a high gear when you leave the clutch out and go till it is running?
Magneto has click after every cylinder and is getting plenty of spark to the plugs.

[Rick Spivey]

Yes, use high gear. Attach your tow rope or chain to the drawbar and run it under the tractor out the front. Good Luck.