Trans modulator vacuum
 

What should the vacuum be to the modulator on a TH350 trans? I checked mine the other day, and was getting between 8 & 12 using a Sunpro under dash gauge. My vacuum line is coming off of the port under the electric choke on a Carter AFB. Is this about normal? It was fluctuating, as my 283 was idling erratically going between 800-1200rpm's at idle. I know stock rpm's are supposed to be 500, but it stalls if I drop it to that range.
Any info would be appreciated.
Thanks

Re: Trans modulator vacuum
 

The Modulator needs Manifold Vacuum.
#8 intake runner is the correct location for the Modulator Vacuum Source.

Re: Trans modulator vacuum
 

[QUOTE= It was fluctuating, as my 283 was idling erratically going between 800-1200rpm's at idle. I know stock rpm's are supposed to be 500, but it stalls if I drop it to that range.
Any info would be appreciated.
Thanks[/QUOTE]

Best way to cure your erratic idle is to max out your initial timing. Somewhere close to 16 to 18 degrees initial. That will speed up(and smooth out) your motor, then you can turn the idle down and adjust your mix screws.

Re: Trans modulator vacuum
 

Thanks guys. One problem. My intake is a stock cast iron for a 4 bbl, but there is no port for vacuum. That's why I am running it off of my carb.. I have been thinking about an Edelbrock intake, or a stock cast iron with a port for vacuum. I gues ta ill be my next purchase.

Re: Trans modulator vacuum
 

If it is a stock intake, there should be a port between the distributor and the carb. Look for a pipe plug if theres no fitting screwed into it. And a fitting can be had from your nearest autowreckers out of any GM with a v8, from one single port to multiple connections.

Alex.

Re: Trans modulator vacuum
 

Thanks, Alex. I'm going to see about getting my old intake back tomorrow, and it has the port on it. I should be good to go then.