stingray_jim

Hey Guys,

I know this is a trail and error thing (so far I am good on the error part) But I am hoping someone my have done the leg work on this. My 68 Conv't stumbles getting into the power band. I have a stroked 383 with a modest cam, 9.5 compression that runs on regular gas (93 octane), my cam isn't too crazy and the thing is timed perfectly. The carb is a 750 vacume (4160 I think) but I don't know the jets etc. Once I get past the stumble it runs terrific. But the stumlble is driving me crazy. So I ordered the pump cam kit and a .31 and .35 squirter from Jegs. When I pulled the squirter that was in the carb it was a .31. So now I only have one size I can go up to. So I did go to the .35 and put the pink pump cam (which the boys at Holly told me was the biggest for the 30cc diaphram I have). It still stumbles. I get flow as soon as the lever moves. So I am kind of at a loss. SHould I go to a bigger squirter. I think Holley says after the squirter goes to .40 you may need the 50cc diaphram.

Any way, any ideas??? I know the set up differs from car to car but I feel like I am way out of range. I have the stock tranny and 3:63 rear. So I figure somone may have gone done this road.

Manny, many thanks.

Jim

Jason Staley

Does it stumble under light or large throttle movements? If you smash the throttle and it bogs, it might be related to the spring in your vacuum secondaries allowing them to open to soon or fast. Hopefully someone with a vacuum secondary carb will chime in. I'm not real familiar with them because I've used only mech. secondary holley's.

stingray_jim

I don't know I haven't mashed it yet. It does as I roll into the throttle. Which is the whole reason I put the 383 with the level torque curve in the car. I wanted that smooth roll in rool out response.

Thanks for the input.

Jim

redwingvette

You might be going the wrong way with the sqirters. Off idle stumbal can be from to much fuel to fast. I had to go smaller and use a lower lift cam to fix mine.

stingray_jim

Redwing - do you recall what size squirter and color cam you wound up with?

Thanks

Jim

BigBlockk

How is the ignition timing set up?

BigBlockk

Later.....

stingray_jim

I've got at the following:

12 - 14 degrees initial @ 1,000
30 degrees @ 2,000
36 degrees @ 3,000 and plus

It runs great after the initial push on the throttle.


Thanks for the response.

Jim

stingray_jim

I've got at the following:

12 - 14 degrees initial @ 1,000
30 degrees @ 2,000
36 degrees @ 3,000 and plus

It runs great after the initial push on the throttle.


Thanks for the response.

Jim

redwingvette

You and I don't have the same setup so mine wont help you.
That said, I have the 4175 vac sec, it came with a size 40 discharge nozzle and I am using a size 21 now (big change) I am using the black cam, I don't remember what it came with.
Before the changes I would blow black smoke everytime I jumped on the gas.

Barry's70LT1

This may help as well.

http://forums.corvetteforum.com/show....php?t=1711868