340 6 pack tuning

[ohio cuda]

Okay wizards let's put our thinking caps on.
340 TA eninge with correct ta heads
4-speed
6-pack was rebuilt back in 1990 vacum operated not mechanical
dual point distributor
Direct connection cam don't know specs.
Now the problem- vibration at 2500 rpm through about 3500 rpm and them smooths out and purrs. Vibration is not as prevalent during hard acceleration.The vibration is not in the drive line. I was told the two outboard cars may need to be rebuilt. Who has a good book on rebuilding these carbs?
Another question is how do you blow out the Power Valve and where is it and what is it's function.
Your thoughts are welcome from our expert panel.

[Robb]

while sitting in the car, revving and  car not moving ?      or while rolling down the road ?    or both ?



I had a vibration that I couldnt find for the longest time, that also was tame under acceleration.     Turned out to be a bad idler arm that I found on accident.   didnt allow lateral movement but did allow vertical slop, so I wasnt seeing the tires wear funny or anything either.

[Chryco Psycho]

Make sure ti is an engine problem as suggested ,
you need to take a manifold vacuum reading at Idle in gear if auto & adjust[change] the power valve to 1.5 " lower minimum to work correctly , with low manifold vacuum the power valve opens to enrich the jet circuit , if it is open at idle it will run very poorly & rich , the power valve is located inside the center carb on the rear of th emetering block , generally it is easist to remove the rear & center carb to get at it

[ohio cuda]

Thanks for the help.  :beer:

[Chryco Psycho]

you may have a problem with the diaphragms in the outboard carbs as well they may be hardened up & need replacing , you can also change springs to change the opening point of the secondary / outboards