[Hacksaw]

Ok. It's a performance built .040 350 SBC, custom built Pro Systems 4150, MSD Pro billet and 6AL, Blaster 2 coil. Timing started at 35 degrees total at 3000. Pro Systems carb has a slight bog spot right before transition to secondaries. I advanced the timing to 38 degrees and it helped, but there is still a very slight bog. Now, I have a 1406 Edelbrock that I had laying around. And the car runs very strong at 35 degrees timing, crisp throttle response, and zero bog. This makes no sense to me, having spent near $700 for the Pro Systems. I haven't had a chance to talk to Patrick yet. Any thoughts or ideas? Thanks

[OneMoreTime]

Are our secondaries coming in just a skosh too soon..a bog can be a sign of over carbed,,too much carb for the engine to absorb at a particular rpm..

Sam

[Hacksaw]

Originally Posted by OneMoreTime

Are our secondaries coming in just a skosh too soon..a bog can be a sign of over carbed,,too much carb for the engine to absorb at a particular rpm..

Sam

That would sure suck. This engine is a Year One Power Crate 350 with the Edlebrock E-Tech heads and Performer RPM intake. 9.7:1 compression, hyd roller. 413 hp 444 tq is what is on the dyno sheet. I submitted the entire engine specs from the paperwork I got with the engine, vehicle info, with exception of the rear gear which changed after the carb was built. I believe this carb is a 780 cfm.

[OneMoreTime]

All that is needed I think is an adjustment in the timing of the secondaries,,A tuning issue..

Sam

[lg1969]

What is the gear ratio on the rear end?

[vinniekq2]

Patrick is the guy to talk to about "his" carb.When I bought a carb from him I made 1 jet change,nothing else

[Hacksaw]

Originally Posted by vinniekq2

Patrick is the guy to talk to about "his" carb.When I bought a carb from him I made 1 jet change,nothing else

Yes. I'm not making any changes without talking to Patrick. I've read too many things good about him!!! I'm just trying to make her I'm doing things right.

[Hacksaw]

Originally Posted by lg1969

What is the gear ratio on the rear end?

The worst possible gear ratio GM ever used...2.56:1. Patrick said this would not affect The carb he built. I don't know?

[vinniekq2]

gears have no affect on the carb,or road racers would use different carbs.I had 2.73,now I have a decent 3.50

[Hacksaw]

I put a couple more degrees in for a total of 40, which I think is too much, but it still starts and dies fine, has no ping, and carb smoothed out quite a bit. So, now I'm wondering how much is too much timing? Maybe a combo of ignition and carb timing?

[F-BIRD'88]

The DP carb will want a lot lot lot more rear gear ratio.

The distributor mechanical advance curve needs a lot of work.

Not enough inital at idle. You want 24-26deg at idle 34-36deg at max advance
a 10deg advance curve.

Your MSD distributor requires a sepecial $33 distributor advance stop bushing to achieve the required timing curve.

If you must use a 2.56 gear ratio get a vac sec carb. 600 to 750cfm vac sec holley or 600-750 edelbrock.

The double pumper will work if you get a agreessive rear gear and a high stall converter.

4.10's and a 10" 3500 stall if you want to go fast.

The bushing to set up the distributor timing curve is found here
http://www.4secondsflat.com/MSD%20Di...r%20Tuning.htm

[cobalt327]

Originally Posted by Hacksaw

I put a couple more degrees in for a total of 40, which I think is too much, but it still starts and dies fine, has no ping, and carb smoothed out quite a bit. So, now I'm wondering how much is too much timing? Maybe a combo of ignition and carb timing?

When adding total timing helps, this is really telling you that you really need to be adding initial timing. Then limit the mechanical advance to keep the total timing from being too high.

The info here was originally on the GM HEI but the timing info applies universally.

Get the timing sorted out first then concentrate on the carb tuning. Readjust the idle mixture screws for highest vacuum/fastest idle rpm as you work on the timing but leave the other carb circuits alone until the timing is done.

You might need to add duration to the accelerator pump(s). This is done with either a pump cam change, or to a smaller shooter. More on tuning the Holley accelerator pump here.

Good luck.

[Hacksaw]

Originally Posted by F-BIRD'88

The DP carb will want a lot lot lot more rear gear ratio.

The distributor mechanical advance curve needs a lot of work.

Not enough inital at idle. You want 24-26deg at idle 34-36deg at max advance
a 10deg advance curve.

Your MSD distributor requires a sepecial $33 distributor advance stop bushing to achieve the required timing curve.

If you must use a 2.56 gear ratio get a vac sec carb. 600 to 750cfm vac sec holley or 600-750 edelbrock.

The double pumper will work if you get a agreessive rear gear and a high stall converter.

4.10's and a 10" 3500 stall if you want to go fast.

The bushing to set up the distributor timing curve is found here
Tuning MSD Distributors

Thanks for the info. I do have a 600 elect choke Eddy sitting on the shelf as a back up carb. As for the gears, my car that burned up had 4.10 rear and I was hoping to use it. However, the fire burned the car and the rear axle didn't make it like I hoped. The gear in my 70 Chevelle that I bought is a 2.56:1 and I don't want to run this. It's just temporary until I can pick up another 12 bolt with around a 3.55:1-3.73:1 rear gear and Posi or Powertrax locker. My converter is a rebuilt glide converter and it's 2500 stall in a turbo 350. Should I run the Edelbrock 600 with some jetting and metering rods and tune the MSD until I get the proper rear gear? Sounds like I need to do that... Thanks again

[lg1969]

Like F-bird 88 wrote, You need gears of you want to run a DP type carb. The 3:55- 373 gears will work. For now with the 2.56 gears use the eddy 600.

[cobalt327]

If you just mat the gas from a stand still or at lower rpm, it may bog because of the gears.

But if the bog is there when the carb transitions into the secondaries- even w/the engine up into the powerband- then there's a problem or problems that need to be addressed.

The carb size needs to be verified, too.