timed vacuum or constant vacuum?

tarps3 · Post by **tarps3** » June 22, 2009, 4:24 pm

I have a 352 with a Comp Cam (little lumpier), new Edelbrock 390 intake and Edelbrock 600 carb.
I have the stock distributor but run Pertronix Ignitor and flamethrower coil.

My question:
Which vacuum port on my carb should I connect the distributor to?
The timed port or the constant vacuum port?

Initial timing is set at 12 degrees BTDC but seems to run a little rough at higher speeds. I've monkeyed with the timing back and forth...

I thought maybe I should swap the vacuum hose (currently hooked to the constant vacuum port).

Any thoughts?

ICEMAN6166 · Post by **ICEMAN6166** » June 23, 2009, 11:47 am

try no vacuum at all.
my bored out 390 (crate engine) has been like that since right after i had it and was having issues and took it to their service shop. they told me it had plenty of advance without the vac hose to the dizzy.
that was about 5 years ago.

tarps3 · Post by **tarps3** » June 23, 2009, 12:02 pm

so just plug the vacuum line coming from the distributor?
doesn't the vacuum advance need that "signal" from the engine?

ICEMAN6166 · Post by **ICEMAN6166** » June 23, 2009, 12:35 pm

i am not using the vacuum advance, so the carb ports are capped.

http://fordtruk.com/forums/album_pic.ph ... user_id=26

Tech · Post by **Tech** » June 24, 2009, 12:04 am

The vacuum advance is what gives you part throttle economy and a smooth idle. If your a drag racer it is of no use because your always under full load. The mechanical advance and initial advance set the total advance the motor will see under full load. back off on the throttle and the vacuum advance starts to come in. If it comes in too soon the engine will ping, too late and the fuel economy will suffer. If you have a high compression engine then put premium in the tank and try both ports. The carb port will probably be less sensitive than straight manifold vacuum. If it won't ping (likely with a stock ford distributor and timing) you'll need to install a spring kit in the distributor. I bought mine from Mr Gasket. It brings the mechanical advance in sooner, without it your engine is either hard starting or doesn't make good power.
Jeff