Technical GMC 228 Jet Size

Hey guys, quick-ish question. I have a rebuilt '52 GMC 228, .40 over running a Rochester B. The Rochester came with a 54 which is huge, the original Zenith 28 228 carb that came with the car from the factory had a size 30 (unfortunately I don't have one). What size should I buy? I'm at a loss here. Thanks in advance!

 

In Florida ? The 54 isn't that big. On a stock engine, I'd use it.

 

Yeah, it’s .40 over and was consuming fuel like crazy. The car is currently in Medellín, Colombia so we’re about a mile above sea level. It’ll be in Florida soon though.


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Jetting is for air fuel mixture as we all know. Leaving for them stock to the carb is best unless you raise the compression and slight changes are needed. I'd run it and read a plug. #'s 3 or 4 are best on a shared intake port engine like the GMC.

 

Don't let the jet numbers fool you; Rochester and Zenith use DIFFERENT numbering schemes.

The Rochester is in thousandths (if it has not been drilled out); the Zenith isn't in thousandths.

If you have a choice, DEFINITELY use the Zenith.

With the Rochester, the probability that the power valve is non-functional and open all the time is much greater than the probability that the main jet is too large.

Jon.

 

Scotch-Brite the power valve piston, de-burr it's bore. Use ethanol free gas. If idle for months, use Stabil.