MC2100 jet issue??

[IOPort51]

OK so happy humbug everybody!!
I have been out in the shop all morning with the CJ, specifically the new /old/rebuilt MC2100. I got the vacuum leaks under control and have it running fair smooth, It would be better I think if I could use the EGR valve but the header kind of did away with that option, at least for the moment.
OK so to the point, finally, I don't seem to be able to idle below 800 RPMs.
I am kind of thinking I may need to swap the jets to something a bit smaller, any opinions??
Before you ask, I have no idea what size they are right now I payed no attention when I built the carb. It is a 1.08 and it came off a 60s galaxy so it does not even have a bowl vent. the timing is running off the ported vacuum at 8 BTDC.

I guess the question, really is, you guys that have made the swap and decided to lean out the jets, what indicated that you were too rich? I am guessing it was the idle situation I am describing.

 

[elwood blues]

Yes IO, the reason that most of us run smaller jets than what come in the MC2100 is because of that exact reason, not getting the engine to idle low enough. You probably know this, but running the MC2100 carb, I was able to back my timing up to 10~12 BTDC and it ran A LOT better, it also helped get the idle down to 700(ish) RPMs.

When you take the air horn back off and look at the jets the should be stamped. Even the aftermarket ones I've bought have been stamped. The OE Ford ones are stamped 52F for example, aftermarket ones are typically just stamped 48, 52, etc.

Here's a couple of sources for MC2100 jets:
Autolite & Motorcraft Carburetor Main Jets

Ford Motorcraft 2100 2150 2 barrel carburetor Parts Page

MOTORCRAFT/FORD/AUTOLITE MAIN JETS


This really does confirm that I really need to finish that MC2100 thread

 

[IOPort51]

OUTSTANDING!!
thanks Elwood, I kind of thought you would have something to contribute.
How much do I want to drop the size? is .003 too much, is .001 enough?

 

[elwood blues]

Here's the thing with the orifice size on the Autolite/Motorcraft carbs, unlike Holley carbs, the orifice size is the stamped number on the jet. In other words, if your jet is stamped 48F, it's orifice size is .048" and it's an OE Ford jet.

Autolite/Motorcraft jets were available from .038" up to .072" orifice size.

At your elevation in TX, I would recommend anywhere from a 45 to a 48 jet, higher than that and you'll be way to rich at idle, lower than that and you may start starving yourself of power.

I'm basically on the coast here and I run 47's.

Hope this helps IO, Merry Christmas!

 

[dalefan88]

i got 46 in mine with no problems. my idle is about 600 to 700.

 

[IOPort51]

your right you do need to finish the MC2100 thread.
Here is another link that I found useful.

http://street2mud.com/webfiles/MC-2100 set up for a 258.pdf

this page suggests that the main jet size in 46 or 47 at sea level and one size smaller for every 1000 ft of elevation.

So why don't you pretty this up a bit and stick it in the tech thread forum or ask the boss for "sticky" status.

Yes IO, the reason that most of us run smaller jets than what come in the MC2100 is because of that exact reason, not getting the engine to idle low enough. You probably know this, but running the MC2100 carb, I was able to back my timing up to 10~12 BTDC and it ran A LOT better, it also helped get the idle down to 700(ish) RPMs.

When you take the air horn back off and look at the jets the should be stamped. Even the aftermarket ones I've bought have been stamped. The OE Ford ones are stamped 52F for example, aftermarket ones are typically just stamped 48, 52, etc.

Here's a couple of sources for MC2100 jets:
Autolite & Motorcraft Carburetor Main Jets

Ford Motorcraft 2100 2150 2 barrel carburetor Parts Page

MOTORCRAFT/FORD/AUTOLITE MAIN JETS


This really does confirm that I really need to finish that MC2100 thread