MC2100 - Intermittent Warm Start Issue - JeepForum.com
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post #1 of 9 Old 07-04-2020, 07:02 PM Thread Starter
AndrewUVM
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MC2100 - Intermittent Warm Start Issue

Hoping someone might have some experience with a warm / hot start issue with the MC2100, that has started after having the idle adjusted.

Drove about an hour away today to go to a car show, CJ ran great the entire trip. Tried the restart the CJ after 20 minutes and it would just turn over, wouldn’t start.

It started after holding the gas peddle to the floor while cranking it over.

Drove it home, let it sit for 10 minutes and then tried to start it, it fired right up. Let it sit for another 20 minutes and no issues restarting it.

Any thoughts on what could be causing this issue, it’s intermittent which is making it that much more frustrating.

Thanks!

86 CJ7, 258, T5.

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post #2 of 9 Old 07-04-2020, 07:31 PM
BagusJeep
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Could be vaporisation of the fuel, very common issue on a modified Jeep as someone has changed out the factory system. What they have put back in is something you may want to look at and compare to stock.

As stock you would have had a 3 way filter just before the carb and a tank return hose was fitted to the top of this filter. Is this still in place? (Amazing how many people remove them) Is it correctly oriented? It would bleed off vapours at the filter so the carb received only fuel. I would not run a jeep long term without this connection if available.

The other measure taken by the factory was to fit a phenolic spacer under the carb to decrease heat soak of the carb and boiling of the fuel in the float chamber. It is possible to run without it but there is a reason to have it.

Lastly the fuel lines were not routed next to the exhaust. They hugged the cylinder head a bit but avoided the really hot parts. I often see Jeeps where the PO has removed the mechanical fuel pump and lines and put in a lot of hoses running in locations and routes you would not want them to.

I also see Jeeps with high pressure fuel pumps and a few feet later a pressure control valve. When that compressed fuel passes the valve, the pressure drops and vapours emerge. Those things ought to be banned from being in a Jeep with carbs, they make no sense. They can work but only with a 3 way filter and tank return.

Worth checking these basic things before you dive into the carb.
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post #3 of 9 Old 07-05-2020, 02:04 PM
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Awesome post! I have an MC2100 and haven't had those issues because of the exact things BagusJeep mentioned. Mine actually has 2 phenolic spacers - 1 between the intake manifold and 2bbl-1bbl adapter, and 1 between the adapter and carb itself - definitely helps keeping the carb isolated from the extra heat from the intake manifold itself.
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post #4 of 9 Old 07-06-2020, 07:47 PM Thread Starter
AndrewUVM
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It looks like I’ve got the correct fuel filter, looks like the spacer is installed under the carb and don’t see that the lines are run close the the exhaust.





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post #5 of 9 Old 07-06-2020, 11:45 PM
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It looks good, one of the better installs we see on the Forum. Plenty of spacers, correct filter and a tank return.

The only difference I can see is maybe that the filter is pointing down a little and you do not have the U bend line before the carb. These are small details, unclear if they are the source of your problem but you will have about an ounce more fuel in the top of the system if you corrected this.
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1981 CJ7 258ci - Bagusjeep
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1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
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post #6 of 9 Old 07-07-2020, 07:38 AM Thread Starter
AndrewUVM
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I've got a replacement fuel filter that I am going to install as I don't know when the previous owner changed the filter last.

For the orientation of the filter, should the offset inlet be at the top or bottom of the filter - or does this not matter. In mine, it is at the top , while in the graphic above it is at the bottom. I'll try to get the filter to align more horizontal as opposed to the current tilt it has.

Thanks for your input!
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post #7 of 9 Old 07-07-2020, 05:21 PM
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I agree with bagusjeep: your install looks pretty dang good, actually. The fuel filter also looks to be aligned well, with the offset output (return) on top.

Could the electric choke be out of adjustment? If the carb's not [somehow] heat soaking, it's going to want a full open throat if it's already warm.

Eric


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post #8 of 9 Old 07-07-2020, 08:22 PM
BagusJeep
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Absolutely vital your filter is horizontal and the outlet is at 12 o'clock and connected to the tank return. This will bleed off vapours and pressure so you are left with a copious supply of low pressure fuel at the carb inlet.

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1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
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post #9 of 9 Old 07-08-2020, 04:08 PM
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Sounds like the above covers the common and obvious stuff well.

Just one more thing.

Tank venting. If the tank is not venting correctly, it could push gas into the carb. The 'holding the peddle all the way down' comment implies the carb is flooded.

When taking the gas cap off, there should be NO pressure release.

Also, when is the last time the rubber lines between the frame hard line and tank and fuel pump were changed? As rubber gets old, it cracks. It can crack enough so you don't see gas, but it lets air get sucked in.
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