Zenith Bendix Carb tuning guide

I stole this from some harley forum. Good info for the archives in case there are others with these carbs.

And my suggestion is to set the low speed needle (closest to the engine) 1 full turn open from the closed position.

Screw the main jet needle (closest to the air cleaner) inward until the spring is almost but not quite coil bound.
Yeah, I know you do not have a spring. Get one.
After you have the spring, turn out the needle 4 full turns.

The spring...... sitting in the palm of your hand is .640 inches long. A tad longer than 5/8 inch.
It has 6 coils. You can get a suitable spring at a hardware store and cut (grind it) to the correct length.

You are not going to burn a hole in a piston, so don't worry about that.
First you have to crank up the bike and let it warm up to full operating temperature.
Next set the low speed needle. This is done by screwing in the needle until the engine falters. Stop.
Turn out the needle until the engine falters again. Stop.
Now turn the needle midway between the faltering points. This adjusts the low speed correctly.

You may have to readjust the idle speed with the idle screw again.
If so, go through the air screw adjustment one more time.
That should do it.


Now for the high speed adjustment.
Jump on the bike and ride it down the road in first or second gear and run it up to about 3/4 throttle.
If the engine blubbers, turn in the main jet needle in until it clears out.
If it does not clear, do another run but turn the needle out until it clears.
At the point that the engine suddenly runs smoothly and pulls strong you have successfully adjusted the high speed correctly!

Handy storage container for the zenith carbs that came with atp kits!
Thats gonna cost me! :laugh:

wireman wrote: Handy storage container for the zenith carbs that came with atp kits!
Thats gonna cost me! :laugh:

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Hahaha! Hey but you can adjust the hi and low with a finger and a thumb in seconds. That's pretty pimp. Changing jets all the time sucks ballz. :dry:

Nice info. My main jet tube is an "A" now. I took the adjusable one out when I took the straight pipes off after 20 years, After my restoration I have a sorry ass quiet stock muffler system. But that low speed needle adjusts just fine like that.
1975 was the last year HD used the bendix Zenith.
That Bendix works fine with my "Blue Streak" Ignition Points!

Yes We Can! All get along!

Adjusted the main twice since 1981. It came with an "A" in 1975. the Factory had A - B - C for different elevations. 3-4 pumps of the throttle and it starts right up. Even in the cold.
I had an A, I put it back in with the stock pipes.
But all these cycles manage to get along.

z1kzonly wrote: Yes We Can! All get along!

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Hahaha! Now I think I have seen the light on thunder jets to worry less.

z1kzonly wrote: Nice info. My main jet tube is an "A" now. I took the adjusable one out when I took the straight pipes off after 20 years, After my restoration I have a sorry ass quiet stock muffler system. But that low speed needle adjusts just fine like that.
1975 was the last year HD used the bendix Zenith.
That Bendix works fine with my "Blue Streak" Ignition Points!

Man, that is one super clean bike! Ed