[Nick Chapman]

Trying to figure out the correct way to hook it up.

I've got an 83 Chevy pickup with a 350. Edelbrock 1406 carb. Everyone that I have talked to say that the vacumme advance needs constant vacumme. But, when I hook up the vacumme to the right side(constant vacumme) of the carb, it idles like crap.

When I hook it up to the left side(no vacumme at idle, but does have vacumme at higher RPM's), it idles perfect, but gets very poor fuel milage.

Anyone have any idea's?


Thanks,
Nick

 

[perezsteveo]

Its supposed to have constant vacuum

 

[mikeb]

It should be hooked up to the "ported" side not the constant side.

It sounds like your mechanical advance in the distributor might not be working properly. Hook up a timing light and remove the vacuum advance hose from the carb. Rev the engine and observe whether the timing advances or not - this is mechanical advance. If it does not advance or advances very little then remove the dist cap & rotor and inspect the weights & springs and the movement of the mechanical advance mechanism. HEI's are notorious for rusting up in this area.

The purpose of vacuum advance is to give you more advance in a "cruise" situation with high manifold vacuum and thus better mileage. Vacuum advance + mechanical advance + initial timing = total timing.

 

[Nick Chapman]

When I disconect the vacumme how much mechanical advance should I expect to be normal?

Thanks for your help!

 

[BP]

It should be on a sticker somewhere in the fan shroud area, near where the plug gap specs are. I know the TBI motors were all around 10 degrees as were the carbureted engines with EST I'm pretty sure. Being an 83 model though I would probably just set it where it pulls the most vacuum or idles with the least amount of idle ckt adjustment on the carb, then adjust the max curve for the most power.

 

[mikeb]

When I disconect the vacumme how much mechanical advance should I expect to be normal?

Thanks for your help!

It's hard to say; i'd figure at least 10-15 degrees. It wouldn't take long to pop off the cap & rotor and examine the mech advance mechanism for proper movement.

You can change the rate and amount of mechanical advance by installing a weight/spring kit. You can also get an adjustable vacuum advance can to replace the OEM unit. With just the weight kit and playing with the initial advance you can probably find a good balance between fuel economy/power & detonation.

For now i'd just try to make sure the mech advance is working properly and go from there.

 

[Nick Chapman]

Thanks guys!

Nick