MC 2100 question

[jrdscj8]

Is it normal that an MC2100 carb have issues on hot restarts? The Jeep starts fine when cold, but after driving at normal operating temperatures, the jeep will have extended crank times after it sits 10 minutes or so. I'm not sure if this is what is referred to as heat soak, or if this could be an issue with the float level. Any ideas would be helpful. Thanks

 

[richardoutwest]

MC2100's here in Arizona usually have a thick gasket as a heat shield from the manifold. Check your gas line to be sure it is free from heat causing a vapor lock, also check the gas cap. Some hot start problems also come from timing issues.

 

[DHugg]

Is it normal that an MC2100 carb have issues on hot restarts? The Jeep starts fine when cold, but after driving at normal operating temperatures, the jeep will have extended crank times after it sits 10 minutes or so. I'm not sure if this is what is referred to as heat soak, or if this could be an issue with the float level. Any ideas would be helpful. Thanks

In my view, not normal. My 2100 aboard a AMC 304 CID starts on the first revolution after shutdown, and has no ignition enhancements yet. The only time a long cranking interval is needed is after a three-week no-run period in the garage.

Easiest things first; check the choke for proper operation at cold AND hot temps. If the choke is OK, then suspicions might shift to the float bowl, maybe too much fuel for a hot start.

I remember airplane recips needing really delicate application of fuel prime on a hot start, or you'd flood 'em, big time, then have to crank forever to get the mixture back to a vapor.

You'll whip it. All the Big Boys say that the MC2100 is a good carb.

 

[jrdscj8]

Thanks for the input, I'm pretty sure the timing is not the issue in this case though, and the choke is wired wide open. This carb is mounted to a AMC 258 i6 / 4.2l with an adapter and thick gasket mounting it to the factory manifold, should I be looking at maybe building an aluminum heat shield since the AMC 258 i6 / 4.2l has the intake/exhaust manifolds on the same side? If most people with the AMC 258 i6 / 4.2l and MC2100 don't see this issue, then there is hope that I can get this corrected. I had an MC2100 on one of my 304s in the past without this issue. I will look into lowering the float to see if than helps. Something else i have noticed with this engine/carb setup is when offroad and bouncing around, the jeep tries tries to stall somewhat. Another possible issue from float being set too high?

 

[IOPort51]

I have an MC2150 on my AMC 258 i6 / 4.2l and it doesn't care if it is hot or cold. I don't even have to pump the throttle, just turn the key and it starts.

What does the fuel line look like from the pump to the filter, to the carb.
pictures would be nice.

 

[Petescj]

Mine cured the hard starting problem when it was cold. Never had any problem restarting it when it was hot either.

 

[richardoutwest]

If you are having trouble after riding and bouncing around, try an anti bounce spring on the float, they are set up (tension) by fuel pressure.

 

[Petescj]

Can we see some pics of your set up? Ive heard of the fuel filter being upside down and causing a similar problem.

Is it normal that an MC2100 carb have issues on hot restarts? The Jeep starts fine when cold, but after driving at normal operating temperatures, the jeep will have extended crank times after it sits 10 minutes or so. I'm not sure if this is what is referred to as heat soak, or if this could be an issue with the float level. Any ideas would be helpful. Thanks

 

[jrdscj8]

I hope these pictures show what you are looking for. Yes, this set up has two fuel filters. One before the pump, one before the carb. Maybe that is part of the problem, don't know.

 

[Petescj]

Im thinking that filter before the pump is your culprit. It looks to have very old style clamps holding it in place. Maybe factory? None of my Jeeps have had one there.

 

[IOPort51]

If you did not put that filter in there I would think about replacing it, I guess that would have a lot to do with whether I found any junk in it.

Still I don't see that causing a "hot" start problem.

 

[jrdscj8]

I have decided to go ahead and rebuild the carb, and I will probably adjust the float level down just a touch to see if that helps. Also, I am going to eliminate the fuel filter located just before the fuel pump. Does anyone see the filter location of the filter by the valve cover being a possible cause to the hot start problem?

 

[Casuall454]

I agree with the fuel filter prior to you mechanical fuel pump. I have never seen one there remove it, let the fuel filter after the fuel pump prior the the carb do the filtering work.

The hard to restart after motor hot..... Have you checked for vacuum leaks ?

 

[jrdscj8]

I just recently remembered that I never posted what I found to be the problem with my carb. I did, in fact have a vacuum leak at the back of the carb where the heat riser for the choke would have been attached from the factory when it was on my old AMC 304 . I plugged that leak, and it made a dramatic difference, but did not totally cure the hard start issue. A few weeks ago, I had to replace my air cleaner due to the brake booster hitting it after I installed a one inch body lift. The K&N filter assembly that I put on it was the answer to the problem. This Jeep starts great at what ever temperature or condition. So to wrap up, I replaced fuel filters, adjusted float down a little, plugged the vacuum leak, and installed a K&N filter. Each change made a difference, but all together they gave me the result that I was looking for.