holley 750 vac sec off idle hesitation. change squirter size?
 

I'm still working out an off idel bog with my holley 750 vac sec on a 383 with stock vortec heads and a 350/350 cam.
I think the timing is set.
I reduced the primary and secondary jets by 2 sizes.
I still have a hesitation from idle. it seems to smoot out after rpm's are up.

The Carb is new
Model = 80508S
68 front jet 73 rear plate
squirter is the stock 31
I have the weakest spring in the secodary setup.


Do I need to change my pump cam or perhaps my squirters?
Any recommendations are appreciated.




...Thanks for the forum that keeps my vette glued together...

Have you tried adjusting your accelerator pump? That's where I would look before I changed the squirter. Crack your throttle at idle and see if you are getting a good pump shot. If not, the AP needs adjustment (or replacement).

The spring on the AP arm may need to be adjusted. Hold the throttle wide open and at the same time push the arm on the float bowl all the way down. A .020 feeler guage should fit between the arm on the float bowl and the spring/bolt assembly that pivots. Adjust the spring height to obtain the correct clearance.

Seems to be the Thread of the Year...!

The best pratices approach is to adjust the squirter arm tight enough that the most tiny movement of the throttle causes the squirters to get wet just static sitting with the motor off.

You did not say the age of the carb, but the squirter bowls have small rubber check valves that get brittle with time and heat. Very easy to change out. Without the good check valve seal you never get a full instant squirt.

Some motors are very lean picky. So even the idle screws can be turned in to the point of effecting how it runs. Like what made you decide to go down two jet sizes?

What is your carb's list number?
What size jets do you have?
What is your pump shooter size?

Many 750 vac sec Holley carbs use a 31 sized shooter; if that doesn't work, try a 35.

The Carb is new
Model = 80508S
68 front jet 73 rear plate
squirter is the stock 31

Is it under heavy, light or all acceleration?

Anything other than being really gentle.. say 1/8th throttle and up..

OK...
Assuming that you're having a bog right off idle, try a 35 shooter; if that doesn't resolve the problem, enrich the idle mix just a bit. Raising the idle rpm will help too.

If the problem still exists at greater throttle settings, try a stiffer secondary spring.

:cheers:

Like stated above, make sure you are getting a pump shot with the slightest movement of the throttle ( gas pedal to make things easy ) the throttle lever should be adjusted very close to the lever on the pump so any movement you get a shot. If that is OK then move up to 35 squirter, the problem should go away :cheers:

If a 35 squirter doesnt work, check your vacuum with a gauge.. Low vacuum or a vaccum leak can cause an off idle transition problem, which can cause a bog.. Your cam isnt that big so your vaccum should not be low.. Did you verify any extra vacuum ports on the carb that arent being used are plugged?

Yep.
I'm getting a vacuum gauge to test vacuum again. My buddy let me borrow one to time it before... I thing this time I'll just buy one.
I plan t allocate 2 or so hours this weekend to try andtune this thing and I'll post the results.
Thanks to all of you.
timg

Also make sure your centrifugal advance weights are not sticking, or that the spring is not too heavy; too little advance low in the rpm-range can also cause an off-idle stumble.

OK just bought an array of squirters, pump cams, a vacuum gauge a quick change spring kit and a new distributor (although after the purchase I found that it is prob a POS)
and a new throttle bracket while I was in there.
As soon as I get this all in the mail I'm going to start working on it. I plan to take the wife for a day cruize and the last thing I want is issues... ARGH...

When you say timing is set.....what is it set at? Initial timing is what?

That has to be right before you play with carb.

Often just moving pump cam to #2 hole can help.

And don't forget....hesitation can be caused by too much fuel shot also.

JIM

How can one determine if the condition is a "over fuel" vs "lean" condition?
My timing is at 8-9 initial and maybe 32 total. A friend is brining over a better light so we can dial it in with 100% accuracy this weekend.
I must admit that I have a cheap light and need to see where the whole curve sets at.
I may pick up a recurve kit today.

I havn't seen anyone suggest changing the ramps on the accelrator pump. If you go to a more agressive pump ramp with the original squiter and see how that affects the hesitation.

Yeah, I did het the package of colored pump cams. All my parts will be here thrusday.. I hope...
I might need to ask what one (colored platic cam)
to try first though hehehe. I'd assume that the one withthe steepest ramp would be giving me the quickest shot...

Before you get too wild I'd get the carb back to as close to original as possible. There are or should be 3 screw settings on the ramp. Make note of how it is currently and then try going up or down one screw hole and see what happens. I would not go to the most aggressive ramp to start. Little steps one at a time is the best way to work a bog/hesitation out.