Rough running 8N

I recently purchased an 8N which runs rough. The previous owner had it tuned up (ignition and new carb,TSX-241B) about three weeks ago. I completed several checks (thanks N-board) but still have not improved the running condition.

I got rid of the inline filter and verified a ample supply of fuel is delivered to the carb.
Verified each plug wire delivers an intense consistent spark which jumps a 1/4 inch gap, checked timing (by the straight edge method), adjusted points (were at .011" now at .015"), plugs are new and gapped correctly, new distributor cap and rotor installed. Disassembled carburetor and found interior very clean, blew out all ports and jets not finding any clogs (carb is less than two weeks old). Checked for intake leaks in the carb and manifold didn't find any.

Idle adjustment screw is backed out 3.5 turns and the main jet screw is backed out 2.5 turns. With these settings the engine runs rough at both low and high speed with lots of misses and pops. Lowest engine rpm attainable with no choke before stalling is probably around 700 - 900 (by ear). Engine actually runs better by backing the main jet screw all the way out to no thread engagement.

By applying approximately 1/3 of full choke it runs much smoother (satisfactory) and a much lower engine rpm is attainable maybe 500-600. I am assuming it runs rough due to a lean fuel mixture (based on the improvement from applying the choke).

Is it possible that the carburetor needs to have a different main jet installed?
Could using the choke be covering up another problem that is not air-fuel mixture related? Is there anything else I can do to correct this, seems like it should run good?

Thanks for your help.

Paul

One question, when your tractor ran rough did it run fairly smooth if you applied the choke to richen the air-fuel mixture?

If an engine runs rough when the choke is in and runs smooth when the choke is applied does it definately mean that the air-fuel mixture is the problem or could applying the choke be compensating for another problem not related to the air-fuel mixture?

Paul

Basic carb jet settings "1 turn out" and you report 3 1/2 turns on idle and main jet is 2 1/2 turns. plus 1/3 choke enrichment.

My guess is a missing carb/manifold gasket somewhere. With the tractor running, take something like WD-40 with a long straw and start spraying around all mate-ing surfaces around the carb and even where the manifold bolts to the engine. The throttle shaft supposed to have a felt seal that been known to leak air into the carb. If the WD-40 gets sucked in to the running engine, the engine will speed up and you will have found your vacuum leak and can fix it.

Hope this helps, sometimes it can get frustrating, good luck..... ...Dell

I sprayed a fluid around the manifold and carb (everywhere) but did not get any response from the engine. Also I first sprayed a little in the air intake to verify it's effect on the engine (ran much faster and smooth). Do you think there could be an internal leak between the exhaust passages and the intake passages in the manifold , so it wouldn't show up as and external leak? I guess I'm reaching, but I'm out of ideas.

I did take the carb apart again (TSX-241B less than three weeks old) blew out all jets and everything seemed to be clear and OK. Put back together and still ran rough. Tried an independant fuel supply (to rule out the fuel tank) and still ran rough.

Not sure what to try next. Maybe there is something wrong with the brand new carb. Not sure where it was purchased from.

Thanks,

Paul

But on some carbs that I have worked on, you could mis-mount the gasket between the float chamber and the top of the carb, such that some of the pass-thru jet circuits could be blocked off and yet the gasket would fit perfectly otherwize..... ..just a thought..... ..Dell