3020 gas, bad stumble

trak

Member
choke to start, runs at low idle, but stumbles or dies when you try to take off, I turned that big pilot screw out two turns on the carb this morn, seem to help, but not the awnswer,, much better when engine is warm, but still, I know the needle and seat aren't that great cause I changed the needle as the original was sticking. this must be a vacuum leak, guess I could check for that, also the small screw at the top of the carb is pretty hard to work with, I guess this is the low idle setting, whole thing could probly use a carb kit, thanx Steve
 
also when it gets done stumbling, a large amount of white smoke comes out, then it clears, idk, something isn't right, engine sounds great, has lots of oil pressure.
 
When was the last time it had a good ignition tune up? What spark plugs are you using and are they at least one heat range hotter than it originally called for?
 
I agree 100% with that. Years ago we had two 3020 gasers here. One with a zenith carb and the other with a marvel carb. The zenith ran much better and as an experiment we switched the two carbs and the other tractor ran much better after having a zenith carb. I have parted a few 3020's out and the zenith carbs sell fast. Tom
 
I put a brand new plastic gas tank on mine and it cured most of the problems it was having. That and a pertronics module and an alternator conversion. Still uses too much gas. Any body interested in a repainted, nice looking 3020 gas? I'll make you a good deal!
 
I have a '67 3020 Gas with the MS carb on it. Yes indeed it IS picky!

They have a diaphragm accelerator pump operated by engine vacuum changes. When the throttle opens from governor action, the change in manifold pressure lets a spring push the gas behind that diaphragm out through a check valve & delivery nozzle. That diaphragm is on the inner side of the bowl cover. Mine ran absolutely terrible and drank fuel when I got it! I found the diaphragm to be as hard as the right fender making it completely useless. There were two styles of check valves in the accelerator pump circuits of those USX carbs. One a pin and a ball, the other two balls. Mine was missing both ball checks so it sucked fuel through the accelerator pump circuit any time the vacuum was high enough to do so which was about any time it was not under heavy load. The only thing forgiving in those carbs appears to be the float level.

After the new diaphragm, check valve balls (both the springs were there, just the balls were missing) and some float adjusting, luckily mine straightened up & actually runs quite well. I agree with others though, that is one picky carb! Don't forget.... the idle mix adjustment (little slotted screw on top with the lock nut on it) is an AIR needle so "in" makes him rich, "out" leans it down. That alone has a tremendous impact on how it responds to a quick opening of the throttle. Maybe 1/8th rich from best idle? Helps with the stumbling a LOT!

Some had two main metering jets. One adjustable one not. The adjusting needle could be switched from side to side which is part of how they made this a Universal which is what the U stood for in USX. I worked on one for another guy. His was insanely thirsty, smoked a lot. Tended to foul plugs plugs like it was burning coal, flooded almost instantly & killed batteries and fell on its face a LOT. Found one of his main fuel jets had come unscrewed & was rolling 'round in the bottom of the carb so it was drinking fuel through a 5/16" hole instead of 1/8 or less. After working on it I began to wonder how it ran as well as it did!

Yes they like a little choke until warmed up. They're never happy if the thermostat is missing or stuck open.

A zenith is more forgiving and less picky.
 
thanks for all the replies, good info, yes mine has the MS carb, might be able to make a go of it.
 

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