2n backfiring only runs with choke all the way on

Jwalker1974

New User
1945 2N only runs when choke is fully on, lately has started to backfire and die. Usually starts right back up but is hard to say how long it will run. Almost everything is new on it. Out of ideas. Sometimes very hard to start have had to actually cover the carb with my hand to get it enough fuel to run. All filters are clean and it is getting fuel. Just apparently not enough for some reason. Any help would be much appreciated!!!

Thanks

Jeremy
 
Have you checked to make sure you have a good quality blue/
white spark at the spark plugs? That would be first in my mind.
If you do, do you have good fuel flow through the carb when you
remove the drain plug from the bottom? Should flow steadily and
fill a pint jar in a couple of minutes. Is that gas clean and water free?
Another good check would be a compression test.
 
I will check spark again. Fuel flow is good. Have not done a compression check yet. If spark is weak where do i start? It has been updated to electronic ignition. Had same issue when still had points and condenser.

Thanks
 
6v or 12v?

How many resistors do you have in the ignition circuit? (see tip # 30)

" If spark is weak where do i start? "

With the battery.

Pulling out the choke gives you a richer mixture. So, you could have either a fuel or spark problem.

A carb out of adjustment will also cause this problem; set the main jet at 1-1/2 turns out & leave it alone.

A dirty carb can cause the problem as well; start by cleaning the fuel screens. (see tips 45 & 56)

Dirty/old gas, or water in the gas can cause this problem.

Restricted fuel flow can cause this problem; remove the bolt at the bottom of the carb & check for flow. The flow should fill a pint jar in under 2 minutes.

On my 1950 frontmount, needing choke to run is the first sign that the points need adjusting/replacing.

A vacuum leak can do the same thing. Get a hand propane torch and carefully spray it (unlit of course) around the intake manifold at the carb to manifold interface & the manifold to block gasket of the tractor while it is running. Or, you can use carb cleaner or WD40. If it speeds up, you found the leak. Sometimes (rarely) manifolds crack or get rust holes.

Lastly, when all else fails, you could have an air leak around the carb metering section. The likely suspects are leaky throttle shaft seals and/or a worn throttle shaft. Or, just a real dirty carb w/ clogged passages.

Bottom line: Probably 90% of "needs choke to run" problems are fuel related, but do not rule out ignition problems, contrary to what others may tell you. I?ve had that very same problem before w/ a rebuilt carb, fresh fuel & good flow & a tight manifold.......and it was a spark problem. But, that was unusual. Just check the likely fuel problems first.

Please be sure to post back & let us know what the fix was. We all learn something if you tell us what worked!
75 Tips
 
it is 12v. When I hold my hand over the carb to start it it feels like it has plenty of pull. Pulls my palm tight to it. I do know amp Guage does not work. Did not know if that could be causing a problem with spark? Manifold is new, the old one was rusted out. New gaskets as well. Will try some of the ideas I have gotten on here when I have time to look at it again.
 
did a little work when I got home today. Good gas flow from bottom of carb. Nice blue white spark in all four cylinders. Checked for leaks with propane torch, no luck. I have been told maybe valves need adjusted? I'm not much of a mechanic and am learning on the fly.
 
It doesn't need the valves adjusted. It
probably has the original lifters anyway.

Did you miss my post about tip # 30 & the
resistors?

All it needs is the OEM ballast resistor.
Too much resistance in the ignition circuit
gets you a weak spark.
75 Tips
 
Does it have a 6v or 12v coil? If it has a 6v coil, it has between .03 and .05 ohms internal resistance. A 12v coil will have nearly 3 ohms. That's why you use 2 resistors with a 6v coil
 
it is supposed to be a 12v coil. I will bypass it when I get an chance and see what I get. Thanks for the help. I'll let you know what I get.
 

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