Long time no visit...so long story...

After a long winter I decided to upgrade the carb on my 383 5spd C2 from a Holley 3310 to a vac secondary 750 cfm Quick Fuel Brawler.
The car ran pretty smooth with the 3310, but was terribly hard to start after sitting and probably needed a clean out and rebuild anyway.

If you recall, its a 10.8:1 383 SBC hyd roller, AFR headed monster. Z28 intake, ported rams horns, etc.

The 3310 was a 750 vac secondary with 72 jets a 31 squirter and a green cam.

After installing the Q/F , it started right up but had a nasty off-idle backfire. I noticed right away that the accelerator pump arm was very loose, so i set it to spec. I noted that the Q/F has 72 jets, 32 squirter, and the white cam.

I have an old assortment of cams and squirters so I began trial and error.
I also checked the timing and noted that i have 12* at idle, 12" vacuum, and idles at 750rpm.
After a variety of cams and squirters, I found that the Blue cam and a 31 squirter gave the most violent acceleration, but still suffered from off-idle hesitation. In 3rd gear at about 30mph mashing the throttle would chirp the tires before hesitating requiring the clutch. In first and second it would roast the tires. There was also a second hesitation right at 2000rpm, inimical of a mechanical secondary opening. I think this is due to the ridge on the blue cam lobe.

Smoothest operation is with the Orange cam and 32 squirter. No hesitation, good smooth acceleration, but no instant on-off power like with the blue cam.

My notes suggest that the Green cam should provide the bigger longer shot of fuel, but it also had the hesitation.

My gut says the motor wants more fuel as evidenced by the raciness of the blue cam fuel delivery, but i dont want to lose the smoothness of the operation with the orange cam.

Frankly im surprised the cam has that much effect on the acceleration of the motor at all.

Thoughts? Should i go back to the blue cam? adjust the orange to the second hole? go bigger jetting? Add more timing?

Lets hear your thoughts.

 

You need to try different vacuum secondary springs.

 

Indeed you do need some adjustment. The QFT carb had an adjustable vacuum can. No spring changes needed. Put the orange cam back on, then start adjusting the vacuum can needle until the bog goes away, say 1/4 turn at a time clockwise. I put a QFT adjustable vacuum can on my 3310 and it's fantastic

 

orange cam is present now, no bog. Are you suggesting I go back to blue and adjust the secondaries clockwise?

 

No, and sorry for the confusion if it seemed like that's what I said,

Try leaving the orange cam on there, and tweak the secondary adjustment to try to get the bog out. The extra gas from the blue cam may have been masking part of the secondaries opening too fast, but only part. That might explain why you got instant acceleration and then a bog. The gas ran out before airflow through the secondaries was enough to pull gas through the main nozzles. At some point, you may even find you can go to a smaller squirter and even slower cam. If the vacuum can is adjusted right, you shouldn't need any gas to cover the secondary opening, only the primary.

The 3310 has been around for more than 50 years. So what does Holley come up with to deal with the secondary opening rate problem? An ugly, cheap plastic quick change cover for the vacuum can. QFT did it right the first time.