JD 4x2 Gator engine stumbling when hot

bcminnc · May 30, 2012

Gator starts fine, cold or hot weather and idles well. For about five minutes, i get plenty of engine RPM. Then when I snap the throttle it stumbles and I get no rpm increase with almost a knocking noise that is not irratic and pretty consistant in sound. Plug ruled out, and fuel pump diaphrams in-tact as well as the check valves in the pump are free and not stuck. Vacuum line to pump; good. Carb replaced and is 3-4 years old and spotless. Main jet clear and fuel is making it to the bowl from pump. If we let the gator cool down for 20-30 minutes, it re starts fine ad runs strong for a few minutes until engine again hesitates and stumbles. If I quit attempting to accelerate engine in the stumbling condition, it will 'idle' fine in this condition but throttle (RPM) advancement is not possible. I did not replace fuel pump to date and it is a few years older than Carb. Thanks for any input. I hate to admit that I am an aircraft mechanic but this one has me stumped. Do I have an ignition component cutting out when warm? My spark plug is collecting some soot after this cycle of stumbling.

aczlan · May 30, 2012

How is the fuel filter? Have you tried loosening the gas cap, then restarting? Have you tried pulling the fuel line before the fuel pump and seeing what kind of flow you get when it is having issues?
It sounds like a fuel delivery issue to me, specifically, something that is partially plugged and only letting fuel through for a few minutes. That is commonly caused by a plugged fuel tank vent, a plugged fuel filter or junk in the fuel tank migrating toward the outlet and plugging it up.

It could be a spark issue, but it sounds like you have spark when it doesn't want to fire. If not, coils that die or have a weak spark when hot are a well known phenomena, but that can easily be ruled out with something such as: Amazon.com: Lisle 20610 Inline Spark Tester: Automotive

Aaron Z

beenthere · May 31, 2012

Puzzling, as I've been running my 4x2 since 1998 and no replacement of anything. After one winter had some running issues with bad gas, but replaced all that gas and started running fine on fresh gas. Now nothing but ethanol free gas.

One thought, are there any signs of mice building a nest under the shrouds in the engine? This AWAG but neighbor had a problem like that and lost an engine (2 cyl air cooled and mouse next stopped air flow around one cylinder).

bcminnc · May 31, 2012

Thanks for jumping in. Fuel filter is new. I have not checked fuel (pump) flow but when I pulled the carb for a quick look at the bowl and float, I reinstalled carb and seemed to have enough pump flow to refill the carb bowl and start it. within about 20 seconds after turning the key; getting fuel to the 'dry' carb.
I was under the impression that this is a ventless fuel tank. So I was not looking for any tank vent. The Tank Cap says ventless. The Gator 4x2 Gas parts book doesn't show a vent line or maybe I missed it when I looked.

beenthere · May 31, 2012

bcminnc
The Gator parts show a Pressure Relief Valve, part no. AM115608
Part #10 in pic and listed as "Vent, fuel tank"

Is this possibly the culprit? I suspect since the fill cap is just below the seat that they don't want any gas fumes coming out there. I'm not sure how the pressure relief valve would cause your problem, but it is in the fuel line.

bcminnc · Jun 1, 2012

Thanks. I found the vent and it hides in the arm tube for the seat on this gator.
I found the culprit minutes ago. While I was in the stumbling mode gasping for fuel, air and timed spark, I happened to push down on the igniter which is located at the top of the engine on older gators. As soon as I applied pressure to the little chrome tin cover, I got an immediate change to maximum RPM. This igniter sits on top of a small piece of phanolic which insulates it from heat. The diodes or circuit within the tin was either broken or partially burnt but working when cold. The Igniter was the problem. Thanks for doing some thinking with me. This is probably the easiest thing to replace on a gator. One screw and one wire clip. Thanks again.

beenthere · Jun 1, 2012

Glad you narrowed it down to what the problem is. I learned something too.
Did not know about an ignitor.
Will try to keep that in mind in case I have a problem. Sure don't give those things away.