SBC sputters/bogs/hesitation under hard acceleration


inforcer958
05-16-2012, 09:09 AM
Finally got my SBC 350 running again from over the winter, Now that i have it running i have some weird problems. First off when i got the car running i had the timing light ready so i could check / set the timing to around 10-16 deg BTDC. over the past few weeks i have gone on little test drives, turning the timing up a little as seems ness. The car just wasn't running right. So i put the light back on it to check my timing, after i got it to a spot where the car runs decent with gradual acceleration. and the initial timing it at 21-22 deg BTDC!?!?! I have a dial back timing light. Now i know it shouldn't be that high. but that's where it runs well and i don't seems to have any pinging. having the wife rev it up to 3000 rpm the timing without vac adv comes up to 34deg and stays there.

So initial = 21-22
total = 34?

However, it starts ok, it kinda chugs until i give it a few revs, ( is that a problem?), but then when i take it out. and whether from a stop, or from about 30mph if i stomp on it. WOT, is just falls flat on its face, like i shut the car off. then i let off the gas pedal it will come back to life (30MPH situation) WOT from a stop will usually kill it.

I did a bunch of work over the winter:

New trans TH350,
new full length headers
new edelbrock rpm air gap intake #7501
SS fuel line from pump to AN fuel filter - fuel pressure guage - carb

Also, everything in the distributor is new, from ign mod to radio cap / wiring, wires are under a year old, same with plugs.

Edelbrock 600 CFM carb, #1405. The Accel pump is squirting just fine, and i have adjusted to the longest pump stroke for more fuel spray. Also the floats in the carb were moving freely.

The distributor weights / springs are clean and tight. other then the instant start-up idle weirdness it idles just fine. I am using a vac adv, hooked up to ported vac on the carb. I did unplug and cap the vac adv to set the initial timing.

Any suggestions? Thanks in advance!

maxwedge
05-16-2012, 06:45 PM
You should run about 14-16 initial and the rest in the mechanical advance, as you say 34-36 at 3k, 21 initial is too high. The hesitation can be low fuel pressure, low float level. stuck metering rods/pistons, get the timing curve corrected then go from there.

Blt2Lst
05-16-2012, 07:10 PM
Since the distributor was removed to install the intake, I would double check to see if is was installed correctly and not one tooth off. Confirm TDC and see where the rotor is pointing in relation to the distributor cap #1

inforcer958
06-01-2012, 08:47 AM
Turned timing down, and it is still running about the same. I need to throw a light on it to double check what exactly its at.
I have jus recently took the top end of the carb apart, i had a clogs accel pump nozzle. So i had to take the metering rods and springs out, and i checked the floats for stickiness / height. Everything seemed fine.

Checked for vacuum leaks, and to see if the vac adv held a vacuum or if it leaked...

As far as the distributor position. Even if the distributor was one tooth off, wouldn't that just limit the range of timing (retarded-adv) that i would have. and if i needed more, and say the vac adv was hitting the intake. then i would have to remove and re-position the distributor?

I am starting to think it is Fuel pressure personally. Yesterday the car started just fine. i went around the neighborhood a few blocks, and then parked it outside in the rain bc i had some stuff to do in the garage. Few hours later i went to start it again. and it just cranked for about 2 min straight. and pumping the pedal didnt help one bit....I have an inline gauge on the pump to carb fuel line. And sometimes it reads around 5 psi, and sometimes the car is running and it is at 0 or close to it. I don't think the gauge is bad. However my question it. Lets say the engine is running and the gauge shows 5psi. if i give it WOT in park, if the fuel pump was bad would i see the pressure drop? Or if this an under-load situation. Where i WOT the engine while moving or from a stand still in drive, and the fuel pressure isnt there to move the load? Thanks for all the help.

maxwedge
06-01-2012, 06:58 PM
Running fp should be about 6-7psi ,under load wide open 3-5 for sure. Get the timing where it should be to eliminate any questions, clogged sock in the tank causes issues also.

Martin86
11-27-2014, 12:35 PM
I think you should take a longer trip and make shure you let it fully warm up before timing it.
also id check dwell timing and gap if you have points sounds like a good old fashioned pre ignition fire cutting it off due to lack of proper timing at that rpm.if it has hei I would look into timing maybe even the timing chain or dizzy gear on the cam for a sbc 12deg btdc sounds right ,..not 20+ and remember to un plug the vac advance before u time it n block it off?

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