Carb idle mixture screws.

[wondernad]

I am rebuilding my stick motorcraft carb. While cleaning I found damage to one of the idle mixture screws. Probably from overtightening. I am having a hard time finding a new one. Supposedly there are 3 lengths of screws, I can find 2 of them just can't find the one I need. Looking for a 1.262" screw. Or does anyone know if I can replace them with the longer ones? On a side note is there any possible reason why the carb would have 2 different size jets in it? For some reason It has a 48 and a 49.

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[hagar]

since the jets are mismatched, how do you know the idle mixture screws are correct ?
frankencarb ?

 

[wondernad]

That is also a good question. To which I have no answer. I can only assume that they are correct and I hate assuming someone else didn't f*** something up. I did verify that the length I have is correct for "some" of this model carb. But cannot verify if mine is one. BTW it is a MC2150 I believe. I don't know the difference between the 2100 and he 2150.

 

[elwood blues]

A MC2150 has the altitude compensator on it, the MC2100 does not. There are a bunch of different variants of the MC2100 though.

Here's a MC2150, notice the compensator on the back side of the carb.

I know of a couple places that sell idle mixture screws and jets:

Ford Motorcraft 2100 2150 2 barrel carburetor Parts Page

Ford Autolite Motorcraft

As for why your carb had two different size jets in it. It is not uncommon to run two different jet sizes to get the idle down to the specific RPM that the PO wanted it, depending on the elevation above sea level and the desired RPM. I've ran a 47 & 48 before. It's not a big deal.

 

[wondernad]

Good info on the difference. I have the 2100. I called the guy from Mikes carburetor parts and asked him about it. That's how I found out there were 3 different lengths. He also doesn't know where to get one. Maybe I'll call the other place tomorrow.

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[wondernad]

This is why I need to get new ones. You can see the one needle has a grove worn into it. Hard to see but its there. Easier to see when holding them.

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[johnbilt]

I don't think that most carbs are setup with two different jets. However, the difference between a 48 and 49 is very small. You probably will never notice anything. I think most holley books suggest a 4 number difference to see a change.