9n surges after 30 minutes

[Bur419N]

I have 1941 9N which I have owned for about 30 years. This is a working tractor and its primary purpose is plowing snow. Parts have been replaced over the years as required and the tractor generally runs well. Over the last few months I have noticed after I work the tractor for a half hour plowing the tractor starts to surge to the point of wanting to stall. If it shuts down and u start it after 15 minutes it then runs fine. My question: could this be the coil. It seems to be related to heat as it only happens after working the tractor for a bit. Any ideas would be appreciated. I have replaced the coil a few times over the years but have not experienced this type symptom
 

[Jim L WA]

It could be the coil, but could also be the condenser. The condenser is cheaper, but now days it's possible to get a bad one out of the box. Do you have any old ones you've kept over the years?
One way or another, replace the condenser first before spending more on a coil that may not be bad.
 

[RWK in WI]

It could be a plugged vent on the fuel tank. The next time it happens loosen the gas cap if that
solves the problem the vent is plugged.
 

[Bruce (VA)]

My experience is that old ignition switches on N's fail more often than coils when hot.

Either jumper a wire from the battery to the coil to find out......or get out your meter.
75 Tips

 

[Eman85]

I'll narrow it down, it's most likely spark or fuel.
I go for the fast fun easy and cheap tests first. Opening the fuel cap when it does it will tell you if the vent is plugged, might take a minute for it to stop surging. I'd also do a fuel flow test as it might have a partially clogged screen. Ignition switches do fail you can try wiggling the key and the wires on the back, wires come loose also.
 

[ASEguy]

So if you didn't work the tractor it wouldn't do it? I would start by pulling the plug on the carb and make sure I could fill a quart jar
in a reasonable time. If that's good, I would go after spark, starting with points. Surging is typically related to a lean condition in my
experience with some engines.
 

[Tim PloughNman Daley]

Yeah, I'd say it is a fuel issue. How does he figure it is an electrical/coil issue? That should be the carb drain plug or fuel line to carb should put out 1-PINT in 2 minutes with no hesitation or sputtering. Always do the Fuel Flow Test first and if it passes, leave it alone and move on to electrical. If it fails, troubleshoot all possible causes for fuel obstruction, rebuilding the carb a last resort.


Tim Daley(MI)
 

[Abbby]

Second what Tim just stated. Do the fuel flow test right after it quits.
 

[Jim L WA]

[Bur419N]

Thanks for all the good ideas. Update. Went out today and
tractor started up and ran for 10 minutes. Loosened the gas
cap when it started to surge. No difference. Seemed to run
better when I pulled the choke half way but eventually quit.
I changed the fuel filter in case it was plugged. Got it going
again after a bit but it is sick. Havent had a chance to
change the condenser but it seems to be getting sicker.
Thinking it may be a fuel or carb issue. Will pull the bowl off
the petcock and check the screen. Not sure why it takes a
bit of time to show up
 

[Abbby]

Did you clean or replace the filter in the carburetor?

 

[ASEguy]

It's about fuel demand. The harder he works the tractor, the greater the fuel demand. If the demand is restricted, you can get a lean surge, and if
the surge gets more exaggerated while it's being worked, he is probably getting leaner as it starts to lower the float bowl level to the
point of dying. Gravity then refills the bowl and it can start back up. I'm not suggesting it has to be fuel, but a simple check of fuel flow
can tell a lot.
 

[Eman85]

[Bur419N]

[quote="Eman85"](quoted from post at 09:29:15 03/19/23) [quote="CVPost-Bur419N"](quoted from post at 12:34:31 03/18/23) Thanks for all the good ideas. Update. Went out today and
tractor started up and ran for 10 minutes. Loosened the gas
cap when it started to surge. No difference. Seemed to run
better when I pulled the choke half way but eventually quit.
I changed the fuel filter in case it was plugged. Got it going
again after a bit but it is sick. Havent had a chance to
change the condenser but it seems to be getting sicker.
Thinking it may be a fuel or carb issue. Will pull the bowl off
the petcock and check the screen. Not sure why it takes a
bit of time to show up[/quote]
What fuel filter? N tractors have cleanable screens in the fuel system.
Did you do a fuel flow test?[/quote]
My carb does not have a screen in it. At some point it was not replaced but I have an external fuel filter. Did a flow test and all good. Today I took the petcock apart and cleaned it but it look good. Pulled the fuel inlet line off the carb and blew it out. No screen. Before I went to the electrical I thought I would try it. Good news it ran fine. Bad news I m not sure why but I will use it a few times now and see if the surging comes back. New step condenser :?:
 

[Eman85]

Did you remove the whole fuel shutoff assy. from the tank, there's a screen in the tank. Also 2 fuel pickups in there, one is for reserve. Did you remove the glass fuel bowl and remove and clean the screen above it? Do you have an aftermarket inline fuel filter in the steel line from the shutoff to the carburetor? Is that what you replaced?
To do the fuel flow test did you remove the plug at the bottom of the float bowl and then turn the fuel on and see how long it takes to fill a pint jar?