The Stovebolt Site Forums The Parking Lot Big Bolts C-60 ignition timing

Hello fellows,

Been a long time since I posted but I am back.

Have an old 74 C 60 with the 350 (I think) engine. Getting it road worthy and checked the timing. It was 22 degrees initial, which is way too much. Set it to 8 degrees before and checked the centrifugal advance. I only have about 10 degrees with the centrifugal, for a total advance of around 18. I am thinking the total, initial and centrifugal, should be at least 32. Does anyone have the actual specifications on something like this?

I doubt it makes any difference but the engine has a governor, which I have disabled. It also has the HEI distributor. Either this is not the original engine or someone changed it over to HEI. On something this old, many things happen.

Are you doing "real truck" stuff with the C-60? If so, you'll need to disable the vacuum advance on the HEI, and rework the centrifugal advance to provide a total advance of around 34-36 degrees at 2500-3K RPM. I'd suggest setting the initial advance at around 10 degrees, and modify the movement of the centrifugal advance weights to provide another 24-26 crankshaft degrees. (12-13 distributor degrees) The rate of advance, (not the total number) can be controlled by tweaking springs. The only purpose for vacuum advance is to improve fuel economy, something that's just about impossible on a C-60!
Jerry

Yes, I want to haul grain with it this year. Vacuum advance is not hooked up. Your advice is almost exactly what I was thinking would be correct for the total timing and also for the RPM it is all in.

Thanks for the reply.

My '57 with the 283 V8 has the factory governor, it is a combination of centrifugal and vacuum, the distributor has no vacuum advance. Spec timing is 4 degrees before, I don't know what the total timing is but I never get any preignition noise. Some 1974 trucks had HEI from the factory, my new 1974 GMC K1500 with 350 4 bbl 4 speed had HEI, I bought it off the dealer lot when I was a senior in high school.

I'm sorry, but disconnecting the vacuum advance is a terrible idea. When my C60 bus still had the original 327, I switched it to HEI when the original governor failed and wouldn't let the engine rev anymore. Vacuum advance is there to be the load sensitive portion of analog timing control, only retarding to what's in the mechanical weights under heavy load. A properly set up vacuum advance improves drivability and yes, even in a C60, can net you another mpg-and from 6 to 7, that's not nothin'. I remember when some old boy told me to run it with no vacuum advance.. yeah, it was fine wide open, but throttle response was pretty mediocre at more moderate loads, and it was actually kinda gutless off idle. As soon as I hooked the advance back up, I found I didn't have to put my foot all the way in it to accelerate, and moderate loads needed a lot less foot feed to control the rig.

I know I'm disagreeing with the powers that be, at my own peril here.. but this is my two cents worth.

When the advance unit failed, I inadvertently ran the Cadi engine in my bus with no vacuum advance for a few weeks.. couldn't figure out why I was suddenly down from 7 to five mpg!

Tronman, I agree with you. I was mistaken about the governor being disabled, it was never enabled (at least the way I bought the truck) The HEI has a vacuum advance cannister on it and, although it was connected to the governor, it was doing nothing. I would like to connect the vacuum advance but there is nothing on this carburetor to connect it to. I could connect it directly to manifold vacuum. I really don't see anything too much wrong with doing it that way, what do you thinK?

I know it is a different animal but I have manifold vacuum connected to my distributor vacuum advance on my SBC - 383. My carburetor does have a port for the vacuum advance but the port opens right at the throottle opening where the idle speed is set causing significant problems setting idle speed.

The only disadvantage I know of connecting the vacuum advance to manifold vacuum is that it may affect your idle speed setting and in some cases that change is more than the carburetor can deal with effectively.

Go ahead and run the vacuum advance if you choose- - - -but be sure it's connected to ported vacuum. At anything other than light throttle cruise with no load on the truck, it's going to stay in the full retard position anyway- - - - -at least that's what the GM training center instructors have said about it since I started attending the one in Memphis Tennessee- - - - -in 1962! Maybe all the internet gurus know something the people who designed the system in the first place don't!

BTW- - - -the 200+ dyno runs I've done also confirm that fact.
Jerry