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post #1 of (permalink) Old 09-15-2006, 07:57 PM Thread Starter
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Dieseling after MC2100 install

Just installed an MC2100 this afternoon. When I took it for a drive, after running a while it will diesel on shutdown. I also noticed my temp is about 10 to 15 degrees hotter than with the Weber. Here's everything I know right now---
Carb came off of a 90 model with 4.2. Previous owner said he had no problems with it. It only has about 700 miles on it and was purchased from a carb rebuilding shop. I have it on an 87 4.2.

Motor has TFI upgrade, but I think the plugs are still gapped at the stock gap. I don't remember regapping them and the motor is too hot right now to mess with.

Timing is about 9*BTDC at 1500 rpm.

I am running an RV cam 260 duration.

I did not try readjusting carb yet as it was already running good on another motor. I do not know if the other motor had any mods done to it.

Idle is at about 650 rpm.

I don't know if this has anything to do with the problem, but before I got the MC2100 I tried to do the Nutter bypass. With the computer out of the circuit, I could not adjust timing past 6*BTDC and it ran like crap. Nutter has been reversed.

Any good guesses?
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post #2 of (permalink) Old 09-15-2006, 08:04 PM
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Re: Dieseling after MC2100 install

My guess, it's running lean, heating up the piston/carbon. That's causing the dieseling when you shut off the engine.
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post #3 of (permalink) Old 09-15-2006, 08:31 PM
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Re: Dieseling after MC2100 install

Like women - EVERY SINGLE ENGINE IS DIFFERENT. You have to adjust the carb TO THAT ENGINE.

The vacuum advance line - where did you connect it?
Is it on manifold vacuum or ported vacuum - should be on ported - direct to the distributor - bypass any solenoids or controls.

Check to make sure you do not have any vacuum leaks around the base gasket.

The old carb had an anti-diesel solenoid on the side of the carb - pushed against the linkage during normal operation, shut the key off, the plunger retracted to shut the throttle plates. Adapt it to your new carb.

Running hotter says leaner, if still diesels, do a search here for "propane trick." Do it to set the carb up.
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post #4 of (permalink) Old 09-15-2006, 09:39 PM Thread Starter
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Re: Dieseling after MC2100 install

I've got it connected to the ported vacuum. It is straight from the port to the distributor. It'll be about a week before I can spend the time messing with it. I'll try adjusting the carb when I get back home.
My weber doesn't have the solenoid on it. The Carter is long gone, so I can't rob it from there either.
Like I said earlier, I don't know what, if any, mods the previous owner had done to his engine. So I know mine is probably very different.
What would be the best thing to spray around the base to check for leaks? I've heard many things mentioned, but haven't had to use them myself.
The Weber ran rich, so it would make sense that the 2100 would run hotter. I didn't think about that until Leve's comment about leaner meaning hotter. I just don't like heat.
Someone on another board said he had the same problem when his float was set too high. I know that was a problem on Webers. Is it the same for the Motorcraft?
Thanks for your help. Motors are a little different than radios and phone systems.
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post #5 of (permalink) Old 09-15-2006, 10:19 PM
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Re: Dieseling after MC2100 install

A higher float setting is richer.

Best thing is propane, next is starting fluid, but Gumout carb cleaner works. Many carb cleaners aren't volatile enough to work, they are like spraying water.

Try revving it to about 2500 - hold your hand or a CLEAN rag over the top of the carb to choke it off. As you choke it if it increases RPM just a tad, it's fine - not too rich, not too lean. It it rases up much, too lean. And if it just tries to die without a tiny increase first, too rich.

If the old carb was way rich, it may just be carbon in the cylinders - add a couple cans of Techron to the gas tank. It'll burn the carbon out safely.
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post #6 of (permalink) Old 09-24-2006, 08:56 PM Thread Starter
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Re: Dieseling after MC2100 install

I checked the timing again and it was actually about 10* BTDC. I adjusted it to 8* and my heat problem went away. Now to fix the dieseling. I'll be checking for vacuum leaks as soon as possible. It actually idles about 750. Could that be too high?
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post #7 of (permalink) Old 09-25-2006, 05:21 PM Thread Starter
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Re: Dieseling after MC2100 install

No vacuum leaks that I can find. I adjusted the idle mixture screws a little to drop the idle to between 600 and 650. I had originally set it using a vacuum gauge and it idled 750. On the first test run, it shuts down fine now. I'll check it more to be sure. Will using the mixture screws affect anything else? I couldn't use the idle speed screw because it isn't even touching anything.
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post #8 of (permalink) Old 09-25-2006, 05:42 PM
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Re: Dieseling after MC2100 install

http://www.affordable-fuel-injection.com/
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