Carb Tuning

[PaulProe]

I've attached an article from a newsgroup I am on regarding tuning Holley carburetors. They aren't difficult but there are a number of different settings that will greatly impact your engines performance.

I've tried to attach the file as a PDF but the forum needs tweaking to allow it. As soon as Mark changes a setting, I'll add the pdf

Paul

[STL Mark]

Fixed it.
Should be able to attach in the thread now.

[A Snake]

I have the complete carb tuning on disc...came with my new Holley. Don't know that I can dup it or not. It is handy and also available on line at Holly web site.

[PaulProe]

Forgot about the Holley DVD. If you don't have a copy, you can view some of the info on the Holley site: www.holleytv.com/ (http://www.holleytv.com/featured_landing.php?reset=true)

Along the left side is an index of all the videos. Click on Carb Tuning and select "All (5)" The five video titles will show up on the right side. It is a crash course in tuning a carb.

Number 1 tip: Bigger is not always better. Size the carburetor to your engine. (this comment applies to carburetors. I am certain there are other threads discussing this philosophy as it applies to other objects :p :eek: :rolleyes: )

Most small block, street motors CANNOT handle 750CFM The carburetor pages have a pretty good guide on selecting the right size carb. We should be realistic in what we do with these motors. Most seldom see 6000+rpm

Paul

[PrecisionRestorations]

Just for everyone's information, if needed we can offer advise on tuning the carb here at our shop.

You can check out our website at http://www.PrecisionCarRestoration.com

Many of your members can attest to the knowledge that our techs have.

[STL Mark]

How are you with Demon Carbs, radical cams, air fuel mixes and testing, rich/lean setting - Can you tell I need to get a good cab set-up? Maybe you can view next week.

[Purple Venom]

I cross posted this on FFC and CC forums:

Recently, our club in St. Louis came across a dyno tuner in Chesterfield, MO at Lynch Hummer. A couple of club cars (one being mine) went in for a tune. There were many lessons learned and things found that I would like to share to hopefully prevent someone from messing up their engine.

1) BG Carbs - Both cars taken in had BG Carbs, one a Mighty Demon, one a Speed Demon. It was found on both that there were many manufacturing flaws in the carb. The Mighty Demon had warped metering blocks and fuel bowls as well as out of round venturi's and throttle body. The Speed Demon was found to have an accelerator pump housing that was "warped" causing leakage at the accelerator pump diaphragm. Shavings were blown out of the metering blocks and fuel bowls in both.

2) Both carbs were found to be out of adjustment - partially due to their owner's :o One running way too rich, the other too lean. We all know the issues either can cause. How were the cars running you ask? Well, both were running ok, satisfactory we'll say, but not great like we wanted, which is why we ended up taking our cars to the tuner.

3) On my car, the timing was off due to a faulty vacuum advance on the distributor that affected total timing and advanced the timing under acceleration.

4) Also, on my car, the spark plugs were replaced. The old one's had served their life, but were still in ok shape.

On to the good stuff. My car, as is baseline dyno is below, the blue line represents the dyno as the car came in, with nothing done to it. The Green line represents the dyno after the carb was rebuilt and new plugs were installed:
http://i137.photobucket.com/albums/q234/Hawgwild06/CobraPics/TimTune.jpg

After finding the bad advance on the distributor, we determined a new mechanical advance distributor would be best. After that was installed, a final dyno pull and tune on the distributor was performed to achieve the final numbers below in blue. Red numbers show the initial baseline dyno:
http://i137.photobucket.com/albums/q234/Hawgwild06/CobraPics/TimBaselineandFinal.jpg

The car has a crisper throttle response, cruises and starts much, much better. How did it get this bad? Probably my lack of complete knowledge on the carb and lack of proper tools to tune it. The other club member had amazing dyno numbers:
http://i137.photobucket.com/albums/q234/Hawgwild06/CobraPics/MarksDyno.jpg

The whole point is, unless you have the software, the dyno, and the necessary tools at home to tune your car, please, please make an appointment with a professional. It will save you tons down the road. It saved our club two engine rebuilds I'm sure. Any questions, let me know, didn't want this to get too long....

[STL Mark]

Good Job - all true.