Jet up for B head?

C

Commander Toasty

Member
I'm going to rebuild my stock Zenith as a winter project. No big deal there, but I have a question...

I'm running a B head on an otherwise stock engine - Do I need to jet up for that head, or stick with all original size jets? If I should increase a jet what size should I go to?

Many thanks!
 
Commander: I believe that what you will need is just a GAV adjustment. I have found that each motor/carb combination requires a different setting. This will also change with altitude, needing to be leaner as you go up. To find the sweet spot, start by running a warmed up car on a straight level road with GAV shut off. The car should act like it is surging, actually it is partially missing. Open the GAV 1/8 turn at a time until the car smoothes out, you will have to reduce throttle to maintain speed. This will give you the optimum fuel air mixture.

My car with a B Zenith 5.5 Snyder head and B cam likes 1/2 - 2/3 turn open, gets 20mph at 50-55 mph.

Mark in MT
 
Heck I run my GAV full closed at all times, other than starting. And that's where it wants to be. Which is one reason I think it's rebuild time for the carb. Too much carbon deposit, poor mileage. I think my float is off.
 
Commander Toasty said:
Heck I run my GAV full closed at all times, other than starting. And that's where it wants to be. Which is one reason I think it's rebuild time for the carb. Too much carbon deposit, poor mileage. I think my float is off.
Click to expand...


You're probably right about the float but while you're at it you ought to flow test the jets (unless you already know they're correct as original).

Your mods are not some huge change and the original flow amount of the jets should be just right because the original Zenith jets were designed to make the engine run full rich. The gasoline 80 years ago was of lower quality. Moreover, Ford probably tended to require a richer setting to insure better driveability in cold weather.
 
Well I ordered one of the $29 rebuild kits, which includes jets. We will see what is in the carb when I open it - maybe somebody installed a larger jet at some point or hogged it out. But I think the real test will be to measure the float level that now exist before I tear it apart. The car runs great ... but it can run better.
 
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