my 8n runs better with the choke

soqueu

Member
I have an 8n that has 12 conversion and runs pretty rough until I pull the choke closed. Is this a carb problem?
 
Most likely--but check spark with 1/4" gapped plug
before tearing into the carburetor..Spark ought to
jump the 1/4" and be Blue--not yellow..
 
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.

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.

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: As Tom said, 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
 
So far I checked for the vacume leaks. Cleaned the carb and filters.no improvement so letting it cool and check the spark and will pull the distributer and inspect the points.
 
" Cleaned the carb and filters"

What filters?

It has 3 fuel screens (as in the pic)

Does your N have an in-line fuel filter? If so, that could be the problem; see tip # 15.
DSC03068.jpg

75 Tips
 
I did a quick soak on the carb and filters=those screens in your photo. Used compressed air to blow out the openings where needle valve and other openings in the carb (like I have done in past years) gaskets from to manifold/ carb looked ok. gasket that splits the carb in half was cardboard looking with no tears in it. I didn't pull the manifold from the block to inspect the gaskets there. after inspecting the points they got a cleaning with 1500 grit paper lightly. gap was good .015 still no improvement. I might throw another working carb to see if it works but maybe I am missing something....
 
I got a white spark with a 1/4" gap in a test plug. The carb is a chinese carb I put on last year. gaskets on block were installed last year too.
 
some water in your gas that collects in the carb bowl will do that too. choke to run right, until you manually drain the bowl.

I see by your latest post that you have good spark, but I'd like to add for other readers that needing choke to run right will fool ya sometimes. I just was working on one that had all the classic symptoms of restricted or dirty fuel flow. Cleaned the whole gas path, pulled the carb a few times.....'There is nothing wrong here'
When trying new plugs, I noticed that the plugs in it were very black. Well, sure looks like enough gas here.
Even though the ignition checked out, I swapped in another set of good points I had in the spares box, and the problem went away instantly.
 
I replaced the carb with a Marvel carb and it runs good again. I must hae missed something with that chinese carb
 
I have a 2N that has had a replacement choke cable put on to it by a PO... the cable apparantly wasnt long enough to route it properly so it acually works in reverse.... in is choked... out is open..

... add to that the fact that the coil hot wire goes to the light switch.... half the fun is figuring out these old farmer fixes..lol
 
Some of those aftermarket carburetors (the cast iron types) are not forged correctly or have obstructed passageways. It seems you end up wasting money on them and end up back at an old original M/S after all is said and done.
 

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