why does it keep hesistating? help me!

[dbmx66]

okay, so.....

i had the truck outside a few times in the past week, trying to tune it up a bit.
its irritating the crap out of me. theres this hesitation.

when i sit there and get on pretty good just from idle, its hesitates for a second then i left off for not even a second and get back on it and it screams like it should.

when i sit there and spool the convertor up to 2500-3000 rpm then let off the brake and smash the gas it just falls on its face. again until i left off and get back on it.

the timing is set.

i have tried almost all the different accelerator pump cams and squirters. and still havent solved it.

the hesitation only got a lil better by changing out acc. pump cams and squirters.

what do i do!

is it too much carb? the engines a 350 bored and stroked to a 383, full forged eagle bottom end. 11.5 or so compression, high flow cnc ported heads with 2.05int and 1.60exh valves. with a .575 hydraulic cam, aluminum rockers, vic jr single plane intake with a holley 750 double pump on it.

please help me.

[team39763]

Mine acted like that when I went racing last November. It turned out to be trash in my carb and I also had water and other crap in my fuel cell.

[dbmx66]

Originally Posted by team39763

Mine acted like that when I went racing last November. It turned out to be trash in my carb and I also had water and other crap in my fuel cell.

mine has a fresh holley carb on it, i milled the choke horn off, i made sure every piece was clean and intact before putting it back together.

[vin63]

May I ask what size jets you have in the primary versus the secondary? Also, what is your fuel pressure at the bowls?

[dbmx66]

Originally Posted by vin63

May I ask what size jets you have in the primary versus the secondary? Also, what is your fuel pressure at the bowls?

jets are 70s and 72s, pressure is 5-6psi

[68longhorn]

Have you tried different timing settings? I was chasing a simalar issue on a far less radical setup. Swore it was carb related, eventually started different timing settings and that fixed it

[dbmx66]

Originally Posted by 68longhorn

Have you tried different timing settings? I was chasing a simalar issue on a far less radical setup. Swore it was carb related, eventually started different timing settings and that fixed it

well the timing was set where we wanted it, i have and msd pro billet distributor in it, it came with different springs and what not, do you think the timing is coming in quick enough?

[vin63]

Originally Posted by dbmx66

jets are 70s and 72s, pressure is 5-6psi

Is the 5-6 psi at idle? What type of regulator system do you use? Since it doesn't require a bunch of changes, I would try going down jet sizes on the primaries first to see if there is any change by increasing the spread between the primary and secondary jet sizes.

[dbmx66]

Originally Posted by vin63

Is the 5-6 psi at idle? What type of regulator system do you use? Since it doesn't require a bunch of changes, I would try going down jet sizes on the primaries first to see if there is any change by increasing the spread between the primary and secondary jet sizes.

its 5-6 psi at idle, its a barry grant pump into a barry grant regulator, should i decrease the jets in the front? or increase the ones in the back?

[fryco]

Did it back fire at all at start-up (ever)? My will knock a power valve out if you look at wrong... Or possible wrong power valve for manifold vacuum. just a idea...

[dbmx66]

Originally Posted by fryco

Did it back fire at all at start-up (ever)? My will knock a power valve out if you look at wrong... Or possible wrong power valve for manifold vacuum. just a idea...

i doesnt back fire at start up, but if i really get on it, it spits out the carb a lil, i thought i might have been hanging a valve hence the spitting out the crab, i checked all my valves and they were all fine. so i have no clue

[cableguy0]

Where is your timing set at?

[1970C10truck]

I'm also curious to hear your timing specs. Did you actually verify tdc with your balancer and timing mark? Or check the balancer hasn't slipped?
Posted via Mobile Device

[vin63]

Originally Posted by dbmx66

its 5-6 psi at idle, its a barry grant pump into a barry grant regulator, should i decrease the jets in the front? or increase the ones in the back?

Do you have a fuel pressure gauge at the carb? I'd be curious to see what the pressure drops to initially when you even snap it up to 2500 rpm...I've had to rebuild a few BG regulators in my time. The spread increase in jets would be just to see if there is any change in throttle response. Just trying to diagnose what is causing the delay.

[1Bad62Pro/Street]

http://www.ehow.com/facts_5161686_ca...elerating.html

http://www.holley.com/TechService/FAQ.asp

http://www.holley.com/TechService/

Sent by Enhanced Email from my Verizon Wireless HTC Thunderbolt 4GLTE smartphone.

[68longhorn]

I only changed base timing. at 8* it had a hesitation, at 10* my issue went away. What is your timing set at?

[1970C10truck]

I run my timing at 12* initial 36* total and because I mostly drive on the street I have my vacuum advance hooked up. Vacuum advance is on full manifold and limited to 6*.

Your 8* sounds a little low in my opinion for the motor you listed.
Posted via Mobile Device

[dbmx66]

its set a 34 degrees at 2500 rpm

[dbmx66]

Originally Posted by 1970C10truck

I'm also curious to hear your timing specs. Did you actually verify tdc with your balancer and timing mark? Or check the balancer hasn't slipped?
Posted via Mobile Device

tdc is at the 0 degree mark on the balancer

[dbmx66]

Originally Posted by vin63

Do you have a fuel pressure gauge at the carb? I'd be curious to see what the pressure drops to initially when you even snap it up to 2500 rpm...I've had to rebuild a few BG regulators in my time. The spread increase in jets would be just to see if there is any change in throttle response. Just trying to diagnose what is causing the delay.

i have gauge at the regulator, i already sent a barry grant back cuz it was junk, this one works, i just dont know if i should go smaller in front or bigger in the back

[shortbed70]

Sounds like you need to either move to a smaller accelerator pump cam or larger one. If it spits out the top try going smaller first. I also had a 750 holly dp that did that turned out to be a warped base plate sucking air.
Posted via Mobile Device

[dbmx66]

Originally Posted by shortbed70

Sounds like you need to either move to a smaller accelerator pump cam or larger one. If it spits out the top try going smaller first. I also had a 750 holly dp that did that turned out to be a warped base plate sucking air.
Posted via Mobile Device

im gonna give that a try tmrw thanks

[fryco]

grab a can of ether spray shoot it around the base of the carb (not in it) while the motor is running. If the motor stumbles your sucking outside air around a gasket. shoot it around the intake where it meets the heads also.

check all your vacuum hoses and caps, make sure nothing is cracked. the simple things will make you scratch your head....

[shortbed70]

Well any updates? Did you figure it out?
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[Mykk]

My vote for ignition timing as well.

I have a vortec headed .040" over 350. 11:1 compression, XR276 roller cam. Mighty Demon 750. I had a bog/hesitation/ stumble off idle too.

Previously I had the distributor set up for 36 degrees max @ 3000rpm with a 24 degree busing, 12 degrees initial and a B26 vacuum advance on ported vacuum.

I just rebuilt/recurved my distributor, used a 21 degree bushing. Set the mechanical to 36 degrees max @ 3000rpm. I also used an adjustable vacuum advance maxed by 8" vacuum and running manifold vacuum. Cleared up all hesitation issues. The engine now fires up, idles and revs faster than it ever has in it's life.

It has 36 mechanical max, 15 cranking. 30 degrees at idle and between 38-51 degrees while low load high vacuum cruising.

YouTube - Vortec 357. New Engine Tuning

Also, if I may suggest. If your SBC is for street use, consider removing the Vic jr in favor of a RPM air-gap. Single planes are steetable, and they drive fine. But I've solved a hesitation in a built SBC by swapping those intakes. myself, I just went from a Super Vic copy single plane to a RPM air-gap copy with a four hole tappered 1" spacer and couldn't be happier with the engine response. Cheers ~Mykk