Starting problem when warm

I have a 1989 Keep Wrangler that has some modifications done to it. All of the vacuum lines realted to the emissions were removed and the original carb has been replaced with a motorcraft 2150. It passes emissions tests with no problems. The problem is Starting when warm. Either a warm day or after driving. It starts great when cold if I pump the pedal once or twice to set the choke. When warm it cranks for 30 seconds then the engine start to turn slighly faster than the starter. If I let off the key the engine will run under 100 rpms for a few seconds and either die or slowly rumble up to normal. That process all happens without pressing the gas pedal while cranking. If I hold the pedal to the floor it usually starts pretty good.

I can live with the starting issue but I wonder if it is related to this running problem. When I’m in the mountains diving really slow because of rough roads the engine will die. Thus usually happens if I’m running at low rpms but this weekend it happened even when running in 4 low at 1200-1500 rpms.

It also has an off idle miss after starting. Once I start driving there is no miss. Except in the mountains on trails going slow.

Any ideas on why the motor doesn’t like to start and run at low rpms? This is the 4.2L engine. This is my daily driver. I live at 2500 ft and drive in the mountains around 4000ft.


Sounds like the carb is too rich at idle. Could be the idle adjustment is too rich or an air bleed is clogged. Try screwing in the idle mixture control using a vacuum gauge to get the highest, steady idle speed. Re-adjust idle speed after finding this point. Try a hot-start after doing this and see if it helps. If it doesn’t, I’d suspect a clogged air bleed either inside the carb or in the throat.

Most of my carburetor equipped cars started well with 1/4 throttle when hot, the vapors in the manifold from the hot soak needs to be cleared.

Thanks for the advice. The problem with the idle turned out to be dirt in the fuel. Probably because of the work I did on the gas tank.

It still doesn’t like to start when warm. I changed the fuel filter about 30 minutes after driving and there was no fuel in the line from the pump to the filter but there was fuel between the filter and the carb. It doesn’t seem to me that it’s not getting fuel when starting because the bowl has fuel in it.