I'm having an Autolite 4100 1.08 rebuilt, and will install it on an Offenhauser DP intake. The engine is a 300 with Duraspark II with HEI, EFI exhaust manifolds and single 2.5" exhaust. With all that said, what jets should I start with? I live in the dry climate of Az, at 1,200 ft above sea level.

Thanks!

 

Start with the jets that are in it.

 

I think Harte3 took his smart a... pill today.

What I think he means is that there is no pat answer. Tuning a carb on these engines is like fishing; you have to keep testing and changing your tackle until you find what works.

Having said that, I would begin with about .046 jets in the primary. Use a vacuum gauge and a AFR gauge to dial it in. If you're not using an AFR gauge you're guessing. You can buy jets from Summit or All State Carbs, or Bill's online. Great Carb, but check the throttle shaft for up/down play very carefully. And make sure your secondaries are opening. The vacuum thru the air horn is very tricky. They won't open in the driveway.

Many times, because of age, and b/c mustang rebuilders have sent the price up, builders will mix and match the boosters, etc. There is zip reference to refer to to verify the boosters in your carb came on that carb. And if they didn't, tuning goes out the window.

There are two types of 4100 1.08: the big block calibrated one, and the one for small blocks. Yes, Ford made a 1.08 for bb's and calibrated it accordingly. Smog years. You might be wise to check and see which you have by running the numbers on mustangtek dot com.

There are rebuilders and there are bebuilders, each having a different level of skill and the amount of work they put in. Good luck.

 

Thanks. I dropped it off at a reputable carb shop (Rod's Carburetor) in Phoenix. I told them what I planned on doing. They'll take a look at the jets. The tag on this carb cross references to a '66 390.

 

Now we get back to Harte3's remark. Where is your rebuilder going to set the floats? for a 390, a 289? The reason Harte mentioned putting them oem, is so you'll have a reference point. It is needed. Set it up oem, float level and jets and power valve, and run it with an AFR gauge on it so you know how it's running, lean or rich or perfect, and make small adjustments from there. If you don't do that you have no base to compare it to, to work from. **Interesting note: the 1.08 4100 is unique in that it is a square bore, but the primary and secondary venturi are different diameters, making a square spread bore.

 

Exactly!