holley 750 vac sec off idle hesitation. change squirter size?
06-03-2010, 07:47 AM
#21
Instructor
Member Since: Mar 2007
Location: Henryville Indiana
Posts: 223
Likes: 0
Received 0 Likes
on
0 Posts
Strange....my 750 vac came with 72 primary jets .....
I have a small cammed 406 and a Holley intake,36 total timing and converted the rears over to jets with Holleys kit 79 in the rear.
Runs great but had to go to a 37 squirter.
I have a small cammed 406 and a Holley intake,36 total timing and converted the rears over to jets with Holleys kit 79 in the rear.
Runs great but had to go to a 37 squirter.
06-03-2010, 08:06 AM
#22
Burning Brakes
Thread Starter
Parts man will be here today.
Kelso, I plan to put everything back to stock configuration other than installing the quick change spring kit.
I think I'll install the stock stiffer spring to begin with and tune the front half of the carb first.
R9,
Is your carb a 3310 or the 8050 ? They are both 750 vac sec's but have diff base configurations.
Was the nozzle change due to an off idle stumble?
Thanks
06-06-2010, 09:13 AM
#23
Burning Brakes
Thread Starter
Results are in. A bit strange but it works...
A friend came over and helped me tune this car.
++++++++++++++CARB++++++++++++++++++
After tweeking with anarray of squirters and pump cams we ended up with a small squirter. a 25. Everyone told me to use a 35. The car still had a bog. I don't really know a ton about carbs but this seemed to resolve the issue. It has a nice tone when you snap the pedal and it takes off like it should. He told me that heavey cars like my vette like a slower / longer stream (nozzle 25) to transition to the main system.
jets were both leaned out from stick by 2...
68 front 71 rear.
We ended up with the pink cam.
+++++++++++++++TIMING++++++++++++++++
He said we had too much total timing. Many on here had me set base timing with the vortecs at 8-9 with that my total was around 36-37.
we unplugged the vacuum advance and set the base at 13. what a difference. Total is around 34.
He told me that my distributor needs to be recurved but at least we got it in the realm of running correctly.
At one point we we had the base timing at 15. It started rough but it ran like a monster. It was on the edge of detruction and just not streetable so we clicked it back to 13.
________________________________________ ____
Does this sound about correct?
to redefine ...
I have a 383 with scat internals flat top pistons stock vortec heads and a 350/350 cam, a cheapo dual plane intake and the carb is the 750 vac secondary.
++++++++++++++CARB++++++++++++++++++
After tweeking with anarray of squirters and pump cams we ended up with a small squirter. a 25. Everyone told me to use a 35. The car still had a bog. I don't really know a ton about carbs but this seemed to resolve the issue. It has a nice tone when you snap the pedal and it takes off like it should. He told me that heavey cars like my vette like a slower / longer stream (nozzle 25) to transition to the main system.
jets were both leaned out from stick by 2...
68 front 71 rear.
We ended up with the pink cam.
+++++++++++++++TIMING++++++++++++++++
He said we had too much total timing. Many on here had me set base timing with the vortecs at 8-9 with that my total was around 36-37.
we unplugged the vacuum advance and set the base at 13. what a difference. Total is around 34.
He told me that my distributor needs to be recurved but at least we got it in the realm of running correctly.
At one point we we had the base timing at 15. It started rough but it ran like a monster. It was on the edge of detruction and just not streetable so we clicked it back to 13.
________________________________________ ____
Does this sound about correct?
to redefine ...
I have a 383 with scat internals flat top pistons stock vortec heads and a 350/350 cam, a cheapo dual plane intake and the carb is the 750 vac secondary.
06-06-2010, 09:41 AM
#24
Burning Brakes
Off-idle stumble can be caused by any number of things: too rich, too lean, too much timing, too little timing, too much timing too soon, too little timing too late, too big of a carburetor, too small of a carburetor, and so on. The only way to determine the actual cause is tuning the car the way you did, using the experience of others as a starting-point and as guidelines, but then seeing what effect changes have on performance.
So it sounds like you were too rich at throttle-opening, with too little timing. Glad you got it figured out!
06-06-2010, 10:45 AM
#25
Burning Brakes
Thread Starter
If it works, it's correct.
Off-idle stumble can be caused by any number of things: too rich, too lean, too much timing, too little timing, too much timing too soon, too little timing too late, too big of a carburetor, too small of a carburetor, and so on. The only way to determine the actual cause is tuning the car the way you did, using the experience of others as a starting-point and as guidelines, but then seeing what effect changes have on performance.
So it sounds like you were too rich at throttle-opening, with too little timing. Glad you got it figured out!
Off-idle stumble can be caused by any number of things: too rich, too lean, too much timing, too little timing, too much timing too soon, too little timing too late, too big of a carburetor, too small of a carburetor, and so on. The only way to determine the actual cause is tuning the car the way you did, using the experience of others as a starting-point and as guidelines, but then seeing what effect changes have on performance.
So it sounds like you were too rich at throttle-opening, with too little timing. Glad you got it figured out!
Thanks to all of you that helped me get this engine in my car and tuned throughout the last year or so.
06-06-2010, 08:04 PM
#26
I race in a class that forces us to use a vacuum carb if that is what it came with, so hence i have played alot with the 3310-1 carbs. I have found that the pink cam works the best and squrters no bigger than 31, I like the downleg squrters. I have just discoveered the quick fuel vacuum pod that does not use the different springs you buy in a kit. It uses a simple screw to adjust the rate and timing of the secondaries. The adjustment is able to dial in the secondaries much better than the spring kit. I would put in the short white and see if it bogs, if it does go to the short yellow, then the long yellow. By the time you buy the quick remove cover and the spring kit, you could have bought the quick fuel piece for $29 for the silver or $39 for the billet red one. I will never go back, the problem is the springs cannot be fine tuned like the quick fuel piece
01-31-2014, 07:57 PM
#27
Intermediate
Member Since: Jan 2014
Location: AIKEN SC
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
Carb tuning... never ending subject :)
A friend came over and helped me tune this car.
++++++++++++++CARB++++++++++++++++++
After tweeking with anarray of squirters and pump cams we ended up with a small squirter. a 25. Everyone told me to use a 35. The car still had a bog. I don't really know a ton about carbs but this seemed to resolve the issue. It has a nice tone when you snap the pedal and it takes off like it should. He told me that heavey cars like my vette like a slower / longer stream (nozzle 25) to transition to the main system.
jets were both leaned out from stick by 2...
68 front 71 rear.
We ended up with the pink cam.
+++++++++++++++TIMING++++++++++++++++
He said we had too much total timing. Many on here had me set base timing with the vortecs at 8-9 with that my total was around 36-37.
we unplugged the vacuum advance and set the base at 13. what a difference. Total is around 34.
He told me that my distributor needs to be recurved but at least we got it in the realm of running correctly.
At one point we we had the base timing at 15. It started rough but it ran like a monster. It was on the edge of detruction and just not streetable so we clicked it back to 13.
________________________________________ ____
Does this sound about correct?
to redefine ...
I have a 383 with scat internals flat top pistons stock vortec heads and a 350/350 cam, a cheapo dual plane intake and the carb is the 750 vac secondary.
++++++++++++++CARB++++++++++++++++++
After tweeking with anarray of squirters and pump cams we ended up with a small squirter. a 25. Everyone told me to use a 35. The car still had a bog. I don't really know a ton about carbs but this seemed to resolve the issue. It has a nice tone when you snap the pedal and it takes off like it should. He told me that heavey cars like my vette like a slower / longer stream (nozzle 25) to transition to the main system.
jets were both leaned out from stick by 2...
68 front 71 rear.
We ended up with the pink cam.
+++++++++++++++TIMING++++++++++++++++
He said we had too much total timing. Many on here had me set base timing with the vortecs at 8-9 with that my total was around 36-37.
we unplugged the vacuum advance and set the base at 13. what a difference. Total is around 34.
He told me that my distributor needs to be recurved but at least we got it in the realm of running correctly.
At one point we we had the base timing at 15. It started rough but it ran like a monster. It was on the edge of detruction and just not streetable so we clicked it back to 13.
________________________________________ ____
Does this sound about correct?
to redefine ...
I have a 383 with scat internals flat top pistons stock vortec heads and a 350/350 cam, a cheapo dual plane intake and the carb is the 750 vac secondary.
I have a 750 cfm vac secondary on a ZZ4 crate engine on my 75 vette.
I'm experiencing the same kind of hesitation when I snap the accell. pedal.
I was wondering : when you say that you unplugged the vacuum advance and set the base timing at 13. Do you mean that you never plugged the vacuum advance back ? I'm curious because in the ZZ4 crate engine doc, they recommend not to use the vacuum advance and set the base timing at 12, which I found weird but...
