big RPM drop

[Rick_L]

Chevynut, you are WAY wrong on vacuum advance. Advancing the timing when the throttle is closed and manifold air pressure is high adds efficiency and driveability under those conditions.

If you are referring to computer control of ignition timing, the same principles are applied. The timing is advanced depending on MAP input.

The only reason not to have some form of vacuum advance is if you don't intend on using the engine at part throttle.

[Maddog]

Chevynut, you are WAY wrong on vacuum advance. Advancing the timing when the throttle is closed and manifold air pressure is high adds efficiency and driveability under those conditions.

If you are referring to computer control of ignition timing, the same principles are applied. The timing is advanced depending on MAP input.
The only reason not to have some form of vacuum advance is if you don't intend on using the engine at part throttle.

"Not true...it's not needed with a modern ignition system."
Nearly fell out of my chair with that ignorant answer ROTFLMAO

RICKL, don't bother he knows every thing, just ask him.

[Maddog]

Vacuum advance is what's between Cnutrolls ears, stil LMAO

[chevynut]

If you are referring to computer control of ignition timing, the same principles are applied. The timing is advanced depending on MAP input.

It doesn't have a vacuum advance mechanism on the distributor was my point. There's nothing to hook up to vacuum because it's all done with the computer at the same time it uses the MAP signal to fire the injectors. I know timing varies with load. I guess I should have been more explicit in my response.

[chasracer]

Well - a 1350 RPM idle is a bit off the wall for a relatively mild small block. We have full-on racing engines that idle lower than that figure. First off, I would try spraying some carb cleaner around the intake and carb gaskets to see if any tiny leak is detected. Be careful with the carb cleaner as it is volatile. You can try something like WD-40 too but unless you actually spot it being sucked in, you might still miss the leak. Eleven inches of vacuum on the gauge is not great so there is something going on. As to the 200 RPM drop when the fans come on - is this an alternator or generator system? A generator I can understand. If it's alternator, then either the alternator is maxing out on amperage or there is a systemic problem in the wiring or even the fans themselves.