i have a 305 with a .454/.454 cam, 416 heads ported and polished, performer RPM intake, 750VS holley, 3500 stall, TH350 trans. Carb is stock except jets were lowered 2 sizes front and back to keep the plugs from looking too rich. Whether or not the car is in gear stepping on the gas pedal causes a stumble/hesistation where the motor sounds like it will die then catches itself and then will rev up. Should I adjust idle mixture screws? change pump cam color to blue from factory? Increase shooter sizes? any help would be great. It is almost a 2 second delay until RPMs will come up.

 

Make sure the bases are covered...ie float levels,power valve selection,idle mixture...TIMING.

Timing plays a huge role in driveability.Ask me how I know.Are you running a vacuum advance distributor?

If all checks OK,go to a bigger squirter..two sizes larger at a time.

 

float levels are fine, rechecked twice, once before it went in for paint and checked after paintjob. timing is 16 initial, 36 total at 3000 RPM. vacuum advance is hooked up and working as well.

 

Are you getting a squirt from the pump as soon as the throttle moves?

Are you using ported or manifold vacuum for the advance?

What is your cruise vacuum?

 

i get a squirt the second the throttle moves. I'm using manifold vacuum off the holley. Cruise vacuum is around 15-16" I believe. idle vacuum is 8-10" I don't remember the exact figure, I know I tuned the idle mixture for highest vacuum, it was close to 1/2 turn out from the motor stumbling when they were turned in too far.

 

Got to ask: Setting the timing with vacuum disconnected, correct?

You might want to try a 7.5 PV.

 

yes set timing with vacuum disconnected. does the PV play a role even when the motor is out of gear and does not have any load on it? I get a stumble either way. Didn't know if pump shot cam or squirter size was the culprit, but I could change out the power valve just as easily. IIRC it should have a 6.5 in it from the factory, would the 7.5 be that noticeable?

 

xpn',
are you using ported or manifold vac to the distributor?
16 initial is kinda high. Do you know the specs on the dist's vacuum can?
What is the spark-advance doing, when idleing,
then blip the throttle?

is there a way for you to get a vacuum reading,
during the bog?

if you are using manifold vac to the distributor,
is vacuum advance 'full-in' at idle?

my understanding is, you don't want the
power-valve to be open, at low rpm w/ low load,
so the PV number should be lower that vacuum measured.

just for a test, you might try varying the base timimg.
both up and down, then repeat with vac disconnected from the dist.,,, and see what happens to the tip-in problem.

I don't like ported vacuum, btw.

 

i'm using manifold vacuum, and the vacuum can adds 15 degrees, with full vacuum. spark advance increases as RPMs increase, haven't been able to get a reading while trying to blip the throttle and hold the timing gun and look over the fender without trying to fall over the new paint. I'll have to try to get a vacuum reading during the bog when it stops raining/snowing whatever it's doing outside.

 

When you set your idle/air screws did you have someone put it in gear while you adjusted them? Also, what size squirter are you running?

 

1QwikZ yes i adjusted them while the car was in gear, although this converter is very loose on the bottom so it really didn't affect idle speed at all. Just put a tire chuck on the front tire, got out of the car and adjusted them off the vacuum guage. I'm running the stock squirter, i'd have to pull it back apart to see. it's a typical 3310 holley that's maybe 2 years old at most.

 

Well, then I might say that a pump cam change is probably in order.....Apparently the stock one is not aggresive enough...

 

xpn,

try this, remove the air cleaner,
have a helper blip the throttle,
at the same time, pour a few drops of
fuel into one of the primary barrels

 

i'll have to try it out sometime next week since i'll be out of town until sunday but i'll try the fuel idea