Tuning problems

[norwegianc10]

My engine hesitates when I step light on the throttle until app. 1/5 of opening. After that it seems to be ok. If I step quick on the pedal it is working perfect, no bogging at all. This is a bit problematic when parking in the city and so on. I have like no easy driving option. Engine is a 350 with + 060 overbore, 10,8comp. Brodix SPEC aluheads with 215cc runners smallest thumpr cam and Holley 650DP

[mclairmo]

Sounds like a lean condition at light load part throttle. That carb may also be too small for those high flow heads.

[dwcsr]

adjust the squirter

[johny1i]

Don't forget to make sure the vacuum advance is working--mine would stumble from idle through ~2000 rpm until the mechanical advance caught up, even with gentle acceleration.

[prostreetC-10]

Was your Holley new? One problem with used Holleys is that guys will get to messing with pump cams, squirters...etc and not knowing how to adjust them. There should be no slack in your accel pump arm and the arm of the pump housing. You should be able to tap the nut on the pump arm and see gas just start to trickle out the shooter.

Also...what is your initial timing set at?

[norwegianc10]

Originally Posted by johny1i

Don't forget to make sure the vacuum advance is working--mine would stumble from idle through ~2000 rpm until the mechanical advance caught up, even with gentle acceleration.

Got no vacuum advance, MSD distributor with 6AL ignition. 12degree initial advance 36degree total at3200.
The carb size should not matter until wot. But my jet size may be off??
Also got a 1 inch 4 hole spacer under the carb.

[prostreetC-10]

Correct on the carb size. The first circut is the same whether it's a 600 or a 950. It's not the jetting. It's in the transition from your idle circut to the main. This is where Holleys can be tricky. It's that "part throttle"...when the blades are coming off the transition slots. Once again, was it new when you put it on? The power vavle could have a little to do with it. They come with 6.5 hg vavles which usually is good for the "majority" of applications. If you have a little time, I'd find the Holley DVD on You Tube that comes with all their carbs. It's a very good DVD. Might not be a bad idea to just go over the adjustments and mainly to check the throttle blade positions.

One last thing on the dizzy. We might have the same ignition setup. I'm running the 85551 dist with the 6AL box. I'm not sure if SBC are the same as BBC but my motor loves at least 18* initial. I started around where you are but really smoothed out down low when I threw another 6* into it. Do you remember what springs you have in your distributor? I initially put in too light of springs and the advance was coming in when you breathed on the throttle. I bumped the curve up to hold the advance until around 1,800 and all in a little over 3,000. It made a huge difference on my low end stumble. You need to at least start with the carb though. Should be too hard to get the stumble out if you re-check the settings.

[norwegianc10]

The carb was used, but was supposed to be rebuilt, and not used after that. All the gaskets looks brand new.

We have got the same ignition setup, I am running the softest ans second softest spring(dont remember colour) Ill guess I have to fiddle some more with the carb then, check the squirters once more.