The Stovebolt Site Forums The Shop Area Engine Shop Rochester B rich

Has anyone ever had to rejet a B to a smaller main jet, or does it always end up being a float level, power valve or improper base gasket issue?

Thanks,

What's your altitude? Carbs set up for elevations near sea level run rich in mountainous regions. A carb that runs right at Daytona Beach will be way rich in Denver, for instance, due to less air density at 5,000+ feet of elevation. Fuel mixture is calculated by the weight of the fuel and air, not the volume.
Jerry

Thanks Jerry, 700'

I'm not looking for complete troubleshooting on the B, there's plenty of posts on that. Just some of them mentioned possibly re-jetting, and the responses are mostly the notorious issues with the B's, and not many reports of the end results.

"The ABC's of carburetion- - - - -Always Buy Carter!" It was true back in the 1950's, and 60 years of experience hasn't changed much!
Jerry

Yup, come across that lots on here. I try to make do with what we have, especially since we're just wanting to get it road-worthy for spring. Then maybe we'll look into cam, intake, exhaust work. Time to polish up those troubleshooting skills...

Thanks,

With today's fuel, unless one is moving from a low altitude to a high altitude, or Dr. Goodpliers (the evil twin of Mr. Goodwrench) previously working on the carb, rejetting involves going RICHER, not leaner.

Probable causes of running too rich (in order of probability):

(1) pertronix conversion
(2) defective fuel valve/float setting in the carb
(3) warped casting causing internal vacuum leak in turn causing power valve to always be open.
(4) other ignition issues.

Jon.

Is the hole in the base gasket aligned with power valve post in throttle body of carb?

In reference to Carbking's post. To further my education, why would a Pertronix converstion cause a rich condition? I understand points (2)(3) and (4).
Thanks,
Mark

Mark - point 1 is the most likely cause of point 4.

Jon.

It isn't actually "rich"- - - -but failing to ignite the mixture efficiently causes the engine to put a lot of unburned fuel down the exhaust pipe and sometimes makes the spark plugs get sooty or fuel-fouled. Half-donkey electronic ignition systems don't always fire the plugs as effectively as a plain old mechanical point system.
Jerry

Thank you Jerry - the first question we now ask of customers with "carburetor problems" is do they have the conversion. If yes, no point (pun not intended) in asking any more questions until they put a points and condenser distributor back in, at least for testing. Just amazing how many "carburetor problems" this solves! Had an electrical engineer tell me that the electronics required a more stable voltage than is possible from a generator; so for those who just have to have the conversion, consider an upgrade to an alternator.

To give pertronixs their due, we see a fewer percentage of problems with the conversion on mid-60's and later vehicles with both 12 volt systems and alternators.

But getting back to the OP's question, I cannot remember the last time it was necessary to re-jet a customer's original application carburetor leaner than stock except for altitude.

Jon.

Thanks Jon. That makes sense. Or should I say, point taken?

Mark

I have a friend who had an issue with a Rochester B. It had an annoying stumble upon acceleration in first gear and the plugs were always sooty. I suspected the dreaded warped casting.
I climbed into the engine bay while it was running so I could look straight down into the carburetor while opening the the throttle. At idle, I could see wetness (fuel) appear at the parting line of the top casting and the body of the carburetor where the gasket is. As the throttle was held slightly open, the fuel evaporated, but would reappear once the throttle was closed.
I am guessing that wetness (fuel) was coming from somewhere which it was not supposed to, and was then passing through the gap where the gasket could not seal, creating a rich condition at idle, causing sooty plugs, and incorrect fuel/air delivery upon acceleration, causing his stumble.