Cbystrack

i have been fighting to get my car dialed in for some time now (87 iroc z with built 355 holley 670 vac secondaries)

my best time to date on 10'' hoosier drag slicks is a 8.30 on a 100 shot of nitrous. something is NOT right.

spoke to some people at the track and they said i needed to raise my fuel pressue to 8ish on nitrous and 6-7 w/o nitrous so i did and it never fell down like it was doing but would not idle like it used to almost felt as if i was loading up at idle.

i have timing set at 34* at 3000 i have a vac advance delete hei (timing settings with nitrous)

without nitrous i have it at 36* at 3000

i think it may be a spark issue because it is just un responsive, chokes, and then finally picks up killing my 60ft. What is the best way to tell if my dist is bad????


I have MSD ignition, msd overhead coil, factory HEI dist w/vac advance delete kit

TGGodfrey

Timing sounds right at least for starting out tuning. Your plugs will tell you what your timing should be. Every motor is a little different. Typical SB Chevy would be around 38* total timing. 36*should be fine.

8lbs of fuel pressure is too much for that carb. tops should be 6.5-7.0lbs. That is why your idle changed. If you would have checked your float bowl level at 8psi you would have found the fuel level in the bowl was too high and you wouldnt have been able to lower it becuase the fuel pressure is pushing past the needle.

Why did you choose a 670 carb? Thats pretty small in my little opinion. I would suggest a 750 if you want to drive it back and forth to work or an 850-950 for a track car.

Are you sure the vacuum secondaries are opening? Sounds like they might not be.

Terry

ATCFLYBOY02

also check for a vac leak. It might be the cause of the idle issue. and as TGG said, check to make sure your secondaries are opening. Another thing could be is your carb is not dialed in correctly. It could be loading up and when it hits lets say 3000, it clears up and thats when you get a nice flow of go-juice... Good luck!!!

Doc

thatdavidkid

8 psi is too high. If you need more fuel for the nitrous, run a bigger fuel jet ... 36-38 degrees is a starting point like stated above, its up to you to find what timing your car likes best. As for Carb sizing, 670 isn't too terribly small, if you're not pulling any vacuum at higher rpms at wot, I don't see why you would need a bigger Carb.

jon_7687

Has it done that ever since you built the engine?

I'd check the accelerator pump adjustment on the carb. Does it stumble like that if you slowly push the pedal down or just when you stab it quickly.

Thats been the issue with about 95% of the off idle stumbles ive ran into with holley carbs.