Carb questions from an EFI guy...

I've programmed & tuned 3 different "vehicles" from scratch with EFI but when it comes to carbs I'm a bit "quoi?" My 71 has a rebuilt carb that is jetted for Colorado Springs elevation... unfort. I'm now living at sea level. Should I look into rejetting and/or swapping on a different carb? The jeep studders a bit when I first try to accelerate but that could be a problem with compensation. Just looking for some of y'alls advise. I've got a Motorcraft 2100 sitting in my shed right now & access to a machine shop & free materials if anyone would send me pics of what the adapter would need to look like. Thanks as always!

 

Re jetting is an option with the rebuilt. Checking the jet size in the 2100 and getting an adapter plate from Checkers or Advance Auto or one of them is another. Or go whole hog and efi it.
I don't remember which way to go on the jets and can't locate the manual for that at the moment (still unpacking boxes)

 

You go leaner (smaller number jet) with altitude. Less O2 in the mixture, so you need less fuel per volume.

The number on the jet (at least with a Motorcraft and Holley) is the diameter in thousandths. Smaller number means a smaller hole. One jet size is a small change - you probably won't notice a difference. IME there's a range of, say, 3-5 sizes where the engine will run ok. Check the spark plug color to get a rough idea of the mixture. Go for a drive across town and back (well warmed up) and don't idle a lot at the end of your drive; then pull your plugs and look at them carefully. There are lots of spark plug reading charts on the net - do a search and look at a few. IIRC the NGK one shows about 50 examples of a range from lean to rich, and the usual 'pathologic' examples.

You can get jets for Motorcraft carbs from Earl Parker Carburetion, and I think The Carburetor Shop? The base pattern of a Motorcraft is the same as a 2V Holley, so you can use a commercial adapter (small base? Rochester to Holley) if you wish. Nothing wrong with the stock carb though - many here like it and use it.

 

I think I would try to rejet the 2g carb instead of switching to the motorcraft, however, I've read that the motorcraft works ok. It just seems like you're adding more variables and potential for needing to troubleshoot by switching. Going to a lower altitude, as mentioned, will require larger jets.

You said that "The jeep studders a bit when I first try to accelerate". Now that problem sounds familiar. Feel free to say more about this problem (and solution if found).

 

according to the holley 470 i bought, holley reccomends 1 jet size per 2000 feet of elevation. depending on where you were (and assuming it was jetted properly then), you should go a couple sizes larger. you dont want to run too lean though, its not good for you valves. jets are cheap. size up till the smoke is slightly grey at full throttle acceleration (my uncle tells me).

 

I'm making my own exhaust and will be adding an O2 bung. I've got a WB02 so that will make selecting the right jet a little easier

 

Excellent.

BTW the jets can be in there very tight. They are brass and if you don't get them the first time, you'll mangle the slot. I clamp the carb to the bench and use a big, square shaft screwdriver and a crescent wrench. Push down with one hand and use the wrench to turn the screwdriver.

 

if only symptom is a sputter when accelerating check the accelerator pump may have a cloged passage or a bad diaphragm, or on some carbs a bad powervalve, i am not saying the jets are not the problem here,but doubt it