Hot/Warm start problem

So this is a new issue for the 360 - MC2100, about 5,200 miles on both.

We all know about the "dry bowl" after sitting a few days, but lately I've been having some difficulty starting it after its warm or hot after it sits for 15-30 mins. My example is driving it to the store about 10 miles away, plenty of time to get up to normal operating temp etc. I go do my shopping, then come back out, turn the key, and I have to give it gas before it starts. It never used to do that. I would just jump in and turn the key and it would fire right up, no gas pedal.

Since I haven't done anything to it in awhile I don't think I did anything to it to cause this.

Last fall I put on a new carb gasket set, which worked great and the Jeep ran fine after that install. I put a new manual fuel pump in about 2 years ago I guess, again no issues.

I'm thinking its a fuel drain back issue, but there should always be something in the bowl after just 15-30 mins right?

 

"give it the gas.."

By that, do you mean hold open the throttle, allowing more air?

Or - do you mean working the accelerator pump, giving more fuel?

 

working the pump for more fuel

 

I have the same issu as you now....i'll follow the thread for sure!!!

 

Automatic choke? Needs adjustment or replacement?

 

Running hot and boiling the fuel out of the bowl, or vaporizing enough that its acting like its flooded and you need to hold open the throttle to let more air in.

Mine does the same thing. I press and hold the accelerator and it fires right up, but I whish I knew how to keep it from happening in the first place.

 

Not sure the fix...still haven't totally figured it out. Phenolic gasket is in place, engine runs to normal operating temp. I did move the choke one more notch rich...I guess I could reset the mixture screws if I have to.

 

This. I saw you mentioned a phenolic gasket. I'm assuming this is referring to the gasket between the intake and carb. If it's relatively thin, you could ditch it and replace it with a 1" phenolic carb spacer. It will help insulate the carb from engine heat and alleviate some of the issue. I had to do this with the Holley double pumper on the SBC in my Jeep. It helped quite a bit. On really hot days, it still does it though, I suppose from just all the underhood heat. Not really a big issue IMO

 

Mmm. I have some suggestions, but nothing from experience.

You could take the hood off and drive it for a while, to see if the problem goes away. Insulating the carb seems like a good plan. There are thick phenolic blocks available from the aftermarket for the 2V that would help to insulate the carb from the manifold. I used to be able to find those on Fords fairly easily at the SoCal pick-and-pulls, but it's been almost a decade since then. Do you have headers? (lots of under-hood heat...) Do you have the fuel return line? You could insulate the fuel lines to help keep the fuel cooler. More return flow with an electric fuel pump would keep the fuel cooler.

You're sure you don't have a stuck float that coincides with the hot weather? Adjusting the idle mixture won't help, AFAIK.

Maybe you have a hole in the power valve that's dripping into the manifold?

Fuel injection...

 

fab some kind of aluminum heat shield under carb?

 

I considered the spacer under the carb, but have never tried it. Seems like it should help. I agree that changing the mixture probably won't help. The issue on mine seems to be that there's already too much gas vapor (too rich) in the carb/manifold because of the rapid evaporation of fuel due to heat. By flooring the accelerator pedal once, you get another, unneeded, shot of gas from the accelerator pump, but then instant relief from the open butterfly (there's probably a technical name for that, but you know what I mean).

Mine is mostly stock, but missing a lot of the evap stuff (charcoal canister, etc...) Maybe that has something to do with it? Could it be that the AMC engineer's put all that stuff in there for a reason?!!!

It's all a mystery to me.

 

"By flooring the accelerator pedal once..."

In the days when dinosaurs roamed the earth, and all cars had carbs, it was standard practice to always floor the pedal once before cranking, in order to 'set' the automatic choke.

(Have you looked to see that the choke plate is full-open when the engine is hot?)

 

Seems we have two threads going here with similar, possibly related root causes.

I have the plastic spacer along with the gasket. The Jeep used to run very well...but something got out of alignment somewhere leading to my predicament. I think I'll check the power valve and float issues as Tim noted.

What type of electric fuel pump would I use in order to keep the fuel bowl full? Also, would that pump only be turned on with a switch when needed before starting? I'd like to keep the mechanical pump too.

 

My CJ-6 came with the Mr. Gasket fuel pump on the inner fender, ahead of the mechanical fuel pump. Worked fine to prime the float bowl, but it was pretty noisy. Bang bang bang ... would be better if it were not bolted to the inner fender, I suppose. It was set up to run always when the key is on. http://www.summitracing.com/parts/mrg-12s/overview/

 

I agree...if you have to pump the throttle to start it when hot, then the fuel bowl has to be draining out. Most likely a bad power valve as noted above. This would be easy to check, as it takes all of 5 minutes to pull the top off of a Motorcraft 2 bbl. carb.

If you have to hold the throttle to the floor to start it (thus admitting more air into the engine) then you're experiencing flooding, caused by fuel boiling in the bowl of the carb. I've seen this a lot on these carbs. Phenolic spacers and heat shields as noted above can help. Another thing that can help, that most people don't consider, is trying a different gas station. Not all gas is blended the same-Some brands of fuel are more likely to boil than others.