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Old 11-02-2007, 09:57 PM
1970Chevy 1970Chevy is offline
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305 sbc good idle, Dies when in gear

Hey fellas, Ive gotten the best help and advice anyone could ask for from the guys on this site. I have a 305 sbc, RPM air Gap manifold, 750 cfm carburator, hedman headers, stock stall converter, and stock 2.56 rear gears, and most likely a mild cam (all from previous owner).

She sounds great in idle as of today. The problem is that when shifting (th350) from park to reverse or first gear She stalls, or comes close to it.

Currently, When In Park:
The initial timing is set to 12* BTDC.
With vacuum advance plugged in shes at 24* (but havent checked total timing yet while engaging throttle)
The idle is set at 1500 RPM.
The Idle mixture screws are set to 1/2 of a turn from fully closed
Vacuum reads exactly 17" Hg

When I shift into to Reverse:
Timing retards to 9 degrees
Idle drops to 600-700 Rpm
Vacuum is 8" Hg
a noticable amount of smoke comes from the breather of the PCV unit
and Stalls if throttle is engaged

I recently changed the man Rods to one stage Leaner in the carburator. I also have in the lightest springs. I have a feeling that changing jets a stage leaner will also help a great deal. The symptoms of losing that amount of vacuum from park to reverse makes me think that the rods are lifting because not enough vacuum is holding them down, causing too much feul in the A/F ratio and bogging the engine. But I dont get why it would do this just by shifting into gear from park or neutral?

I just checked pretty extensivly for a vacuum leak but didnt find anything. Im researching the different parts of a transmission (modulator maybe?) to see if I can figure something out.

-Matthew
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