Hey everyone,
I finally put enough miles on my car to concider it broken in .
It has incredable low end power (1500 - 2500 RPM), and it pulls like a frieght train above 4000rpm. However, it has almost NO power between about 3000 and 4000 RPM. It kind of jerks and misses in this range and is driving me crazy.

I still have the Holley 600 on it w/ #70 primary jets and a purple VS spring. I now have a Mallory distributor with the medium weights and an MSD 6A box. Base timing is at *12, and full advance is in by 2800 RPM. I have played around w/ the distributor springs and base timing, *12 seems the best and I don't hear pinging. I don't know what my total timing is, but if that was too low it would affect top end too, right?
I don't have any vacuum leaks, distributor, cap, and rotor are new. Wires are OK, but I can't see them being the problems since it only has a problem in that limited RPM range.
Can anybody help?

 

What happens when you crowd the "midrange" at part throttle?
Does it brake down or surge or run smooth?

Blow some compressed air down the airbleeds in the carb air horn
to ensure there is no dirt blocking the airbleeds or down wells.

Get an advance timing light or a crank hub timing tape so you can verify total timing.

 

The midrange is pretty smooth at part throttle, it's only under acceleration when it starts to break up. I do need to get some timing tape, I just havn't gotten around to it yet. I will do that this weekend hopefully.

 

Any other suggestions? The carb is only about 6 months old, I bought it for my Monte Carlo. I did take it apart and blow it out but it did not help. Also, the secondary metering plate is still the stock size, I imagine it's a bit small. Could that affect midrange and not topend though?

Thanks

 

Ok, I don't know what else to do on this carb, it's starting to drive me crazy. One other question, would a 650 double pumper be worth having? I want to be able to tune the secondary jets, but I don't know if I should get the 4150 secondary metering block kit or just get a mechanical secondary 650 DP.

 

Ok, I found out that when it starts to spudder in the midrange, if I floor the accelerator it clears up and pulls real nice. So, I was thinking maybe I need a lighter spring for the VS. However, when it spudders around 3000-4000 RPM, it is blowing black smoke which makes it seem like it's running rich. I might get a secondary metering block so I can change the rear jets, but I don't think that is the problem.

Any help?