I have a 57 F600 M&H with the 292HD that I am restoring. I got it running very good and drove it today for the first time in 48 years. When I was setting the timing, I noticed that it as two vacuum lines. There is a vacuum line going from the RH base plate of the carb to the Dist body and a vacuum line going from the LH body of the carb to the dist shaft housing. I assume that there is no internal vacuum advance.

Also, It has a 1959-1960 governor Holley list 2022 on it. it idles great but it has a horrible flat spot in the mid-range. It could be a power valve issue and I can fix it. However, I have a rebuilt Holley 390 list 8007 that I converted to manual choke.

My questions are;
1: What do the vacuum lines control in the dist?

2: Since I will never work the truck hard, is the 390 a better choice?

3: If I replace the carb, will this dist work fine or should I opt for a vac advance style instead?

 

I think you should change out the carb and dist.

I have a carb that used to be like what you have.
This one used to have a governor, plus a hand throttle. With a LOT of work, including fabing accelerator cam and linkage, still dont know if it will turn out useable. There is no ported vacuum, and to remove the unwanted items the throttle shaft had to be cut flush with the body, eliminating poss. for choke.

I am helping a friend's son with his '62 GMC short body school bus. It has an SBC with governed carb. We are going to change out to a non governed carb. Dont know yet what will be done about the distributor.

 

I read your thread, it was very interesting. It was the reason why I was thinking about installing the 390CFM.

Any ideas what the two vac lines to the distributor are for. It's obviously a mechanical advance only distributor.

 

I dont know. That is pretty much the same reason I said we dont know what will be done on the dist. for the GMC. If I owned the bus the dist. would get replaced. The owner(s) think they can just plug the unused dist. vacuum ports. We will see what happens when the carb is in place and timing light is used.

 

Marc,


I am using a newer style dist (with Pertronix inside) and I bought the following carb for mine. (complete with their throttle position sensor)

Holley Performance Products 390 CFM Four Barrel Street Carburetor 0-8007

It's their 390CFM model.

 

That's the same one I have. I took the electric choke off of it and converted it to a manual. If I get time this week, I will put it on and take it for another spin.

What jets do you have in the primary's? Mine has 51's in it.

 

The two lines to the distributor are for the governor. One line is vacuum from the carb to the distributor, the other is vacuum from the distributor to the governor. When the distributor shaft rotates above the governed speed, the regulating mechanism in the distributor applies vacuum to the governor to reduce throttle opening.

A distributor from a 292MD should work if you change the carb from a governed model to a regular model. Only potential issue is if you have a mechanical tach, the 292MD distributor has no provision for a tach drive.

 

Thanks, That makes sense. I appreciate the response.

 

Put the 390CFM on it, disconnected and capped the vac ports on the dist. Took it for a spin and it runs like a champ. No more flat spot in the mid range and it idles very smooth at 600 RPMs. I then came home and bumped the timing up from the 5 degrees intial to 12 degrees. The total is now 34 degrees. Drove it again and it runs even better and no detonation on reg fuel.

Anyway, one project done and moving on to another. Thanks for the help everyone.

 

Thanks for posting your results. We will try capping the dist. on the GMC and hopefully get the same results when the new carb is in.

 

Great!

That makes me feel good that the new Holley 390 I'm putting on mine will run well!

I'm going to have an electric choke though....