rkk69olds

I am having issues with my 350 stumbling / hesitating off idle. I know this seems to be a fairly common problem and there is alot of information out there, but I still can't seem to solve this issue.

355, balanced, line honed, ec...
Speed Pro forged pistons, advertised CR 10.35:1, never measured actual so I don't know what I have
Erson cam 110+4 lobe separation, intake 224 and exhaust 223 @.050
#5 heads, ported, 2.07 intake and 1.68 exhaust
Harland Sharp 1.6 roller rockers
Edelbrock Performer RPM intake
Mallory Unilite distributor and Hyfire Ignition Box
Edelbrock Thunder Series AVS 650, vacuum secondaries and electric choke
robbMc fuel pump, Aeromotive filer and regulator
Milodon 7qt oil pan, pump and pickup
TH350 with Coan 2800 RPM converter
3.42:1 Gears

Initial timing is set at 12 degrees and all in at 34 degrees and 3000 rpm

I had a Holley 670 on before the edelbrock, but it stumbled as well and I thought it was me just not be all knowing about tuning it. The Edelbrock has made the problem a little worse, but over all the car seems to performer better with it.

Things i have tried:

Multiple timing settings - no change
Spark plugs changed - NGK B7S @ .035 and Autolite 86 @ .045 - no change
Adjusted vac secondaries on Edelbrock passed factory setting to slow opening - no change
Tried all 3 accelerator pump positions - no change
Adjusted fuel pressure to 5.5 psi
Change carb springs and rods in - no change
Change out fuel with fresh 93 octane and added sea foam - no change
Tried timed and full vacuum for distributor - no change
Adjusted idle mixture to achieve highest vacuum - have about 14 hg

I have not yet replaced the fuel filter element, but will do so next

I still think its a timing problem, but changes don't seem to work. I had the timing originally set and dialed in on a chassis dyno, but not sure that matters

Looking for some advice please

Thanks

oldcutlass

Have your moved your accelerator pump setting up 1 notch to give it more fuel?

coppercutlass

X2 with oldcutlass. I had the same issue when i ran the edelbrock. Fwiw ther is a slight diffrece between running ported and unported source for the vac. adv. It made a diffrence for me along with having a slightly better idle quality. i went holley double pumper 650 and never looked back.

Rickman48

Just for the heck of it, pull the distributer cap, and check for play in the shaft - and the inside of the cap for 'crazy' wear.
Also twist the top of the dist. and make sure it's not 'gummed up' and sticking.
I know it's new, but stranger things have happened.
Have you checked that ign. box?
Let us know, please.

rkk69olds

I have tried all 3 pump holes and really no change.

I will pull the cap and looking a little closer at the distributor. What is the best way to check the Hyfire Ignition? I assume I just need to isolate it and run on the distributor / coil only?

Thanks for the input.

olds 307 and 403

How quick does the timing curve come in? Was the cam degreed?

rkk69olds

I don't recall how fast timing comes all in. I will check. Yes cam was degreed in.

rjohnson442

I'm thinking Distributor springs or the weight are getting caught up if it runs fine besides that. They can go out and not come all the way back in AND with a vac advance it can push the timing up to high for a lower rpm.