How to lean mixture on '47 V8

[Old Henry]

My sparkplugs have dry black powder on them which, I believe, is from a too rich mixture. The only way I can think of to lean it out and clean up the plugs is to replace the jets with slightly smaller ones.

Any other ways?

[cadillac512]

If your float level is correct and the power valve isn't leaking then yes, jets are the way to lean it. Generally a jet two numbers smaller is a good place to start...say from 50 to a 48.



Terry

[51woodie]

I had an over rich problem with the carb on my '46, 59ab, that I couldn't sort out. After a lot of troubleshooting with no success, I sent the carb and my pump to Charlie in NY. He found that all was good, except someone at one point in time, drilled the jets oversize. I would have never found that, as I trusted the number on the jets. The plugs are now a nice light tan.

[SoCalCoupe]

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Originally Posted by 51woodie

I had an over rich problem with the carb on my '46, 59ab, that I couldn't sort out. After a lot of troubleshooting with no success, I sent the carb and my pump to Charlie in NY. He found that all was good, except someone at one point in time, drilled the jets oversize. I would have never found that, as I trusted the number on the jets. The plugs are now a nice light tan.

IMHO, the starting point is knowing whether or not you have a near perfect stock carb. There is so much wear, warping, slightly incorrect parts etc. that can creep into a carb over 80 years that unless you start with a nearly perfect carb as a real professional like Charlie in NY could attest to, you're really just guessing. So many things could be wrong that an amateur like myself would never catch.


When I bought my car 2 years ago it had a single Holley 94. I rebuilt it myself, just a simple rebuild kit, but never could get it to run right. I replaced it with a new UK Stromberg 97 and it was like putting a new engine in the car, it ran perfect. Later I replaced that with a pair of Stromberg 81's. It took me a year to get those running right. I fiddled around with everything and finally replaced the throttle shafts with oversized parts that compensated for wear. That finally fixed things up. That may not be your fundamental problem, and probably isn't, but I'm just saying that an 80 year old carb could have a lot of hidden issues that are bigger than a simple rebuild kit, adjustments or jetting.