Try a cheap 4 hole spacer and see if the signal gets stronger to the carb. I had a 1" open on my Nova with the dual plane and it seemed to clean up a little with a 4 hole.

 

Let's back up a minute. How is your distributor setup? Debated to all heck here. I found that any vacuum advance at idle will cause a bog/hesitation as the timing retards. Getting that out of the way, larger squirter size didn't really resolve the issue. On 850 carb, I used the 50cc pump with pump cam to get shot started early and stay with the smallest squirter you can. My thoughts (wrong or right) were to get a larger amount of fuel moving early in throttle position, but keep the smaller squirter to try and give the fuel better atomization. I could be wrong, but seemed to me the bigger pump fed the fuel at a higher pressure through the nozzles. Been awhile, IIRC,I was using 35 or 37 squirters on the 540 motor with no hesitation at all.

 

GM Timing Specs
12 Initial
32 Total

No Vacuum advance MSD 85551
To start I was,
31 Primary, 35 Secondary, then 31 Primary , 31 Secondary, not much better, then 31 Primary, 37 Tube style Secondary lots better but not gone

After reading a bit a 1" open spacer can slow down or weaken the carb signal I might try it with no spacer

 

After reading a bit a 1" open spacer can slow down or weaken the carb signal I might try it with no spacer

I agree with this, but I needed a spacer to clear the vacuum port on the rear of the manifold. I couldn't run without the spacer so I did the 4 hole to try to compensate.

 

Needs more initial timing and bigger primary nozzle. A 37-39 will do the trick.

 

I'll try a larger primary squirter... I like how crisp it is on the primary's around town

 

What I'm not sure of is why GM installed this huge single plane on this crate engine... It looks as big as a Super Victor that Edelbrock sells

 

Its a GM crate engine Zz383,,, vortec heads like 32 total.. As the manual says... It has a B&M holeshot 3600 and 4.10 gears

 

FWIW just redid a dist for same engine / carb more initial helped a lot ( no spacer) limited mech to 10* and set total at 33* VA limited to 10* yes vortec head don't need a lot of total

 

I'll ditch the open spacer.. That should make the intake seem smaller... Then try a bigger primary squirter.. Try a few more degrees timing.... Never ever had bog issues like this...I'm ready to try a 750 hp vacuum soon

 

Try the timing 1st! put it to 20 temporarily. You won't believe the difference!

 

Then feel that single plane pull!

 

Here's the intake the crate engine uses

 

I think the motor will be a lot more responsive with the added initial timing and bigger primary nozzle. I think the motor would prefer and air gap rpm intake as well. Isn't the duration like 222/230?

 

You are correct on the duration. It idles like a stock engine with the 112 LS.
I am not sure why they put this huge intake, I think the Dual Plane would of been a better choice.

The distributor I am using has a 20 degree bushing, so its 12 initial and 32 total, just like the GM manual said.

I might bump it up to 16 initial and 36 total and try that, but right now, I am running a 31 Primary and a 37 squirter.

I started with a 31 and a 35, so I will but the 35 in the front now, and leave the 37 in the back and ditch the 1" spacer , its making this huge single plane even bigger.

Dave

 

I don't have A dbl pumper, but did add a 4 hole spacer on my 355 last week. With the 770SA I had to go from the stock 25 up to the 31 squirter. That got rid of my bog.

The jury is still out whether the spacer did any good yet. Last week was very humid. This week is much cooler.

 

That intake is huge. I think it's strictly an ignition and fuel timing issue.

 

All their motors say 10 base 32 total.

Still way to low.

Keep the 32 but bring up the base. They also say to use P/N 19170093 which is a VS carb... . but the dp will be fine.

 

Removed 1" spacer = No Change
Bumped up timing = No Change, (Because it would do it if I was on the converter @ 2500 so the timing was all in then)
Added larger 35 squirter to front = A bit better still there

Dave

 

I think your issue is timing of the pump shot. You might need to step up to the 50CC pump and use the brown or pink cam. Both of these move a serious amount of fuel.

 

Bigger nozzle yet and ditch that large single plane intake for the dual plane

 

Dave, Have you tried another carb? You bumped timing to what?
Not trying to be a pita...We really want to help...it's just I have a similar intake in size and a "1 open and a larger carb with no issues.

Are you footbraking it then mashing it? That will eat up pump shot also.

Now my timing is locked out at 38deg tho and I could almost guarantee if I dropped it to even 20deg it would do the same thing. Esp with the 269 duration @ .050 SR cam that's in there.

 

Just added a 1" aluminum spacer without a problem. Engine seems to run better on cold start up and seat of the pants at the track last night seemed better. Looks like I may have picked up .5mph on the last 1/8 mile from last week (different days so not conclusive).

 

It's best to start at square one and first make sure that all the other fuel circuits are set up properly before attempting to tune the accelerator pump circuit. Single planes can be a real pain to tune.

http://www.nastyz28.com/~ericf/tech/htune.pdf