Thread: Tuning carb with a vacuum gauge

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I read that I could tune my Edelbrock 750cfm 4-barrel carb by hooking it up to a vacuum gauge, is this true? If so, do I hook it up to the 2 ports at the front of the carb and adjust both screws to get the best result? Also, it is recommended that my measurement should read between 15 and 20 in., but I have heavy cam and higher compression (not exactly sure what size etc.) so would I be looking at a measurement more around 10? What do I look for as far as adjusting the screws; i.e. rise or fall in vacuum readings?

Not done yet, stick with me.

Should I attach it to the manifold port, also, at the back of the manifold and check there also? Will the measuremnets be the same? It also has a pressure gauge on the dial.

Thanks again.

Hook up your vacuum guage to the intake manifold port of the carb (sucks at idle).
Set you rpm about where you want it to be.
Adjust your idle mixture screws to give you the highest manifold vacuum reading (which should be the highest idle rpm reading with the throttle butterflies closed).
Re-set your idle rpm.

Run it a while and read your spark plugs.
If they are sooty, or wet, then lean it out a bit with the jets and metering rods (strip kit)...

Be super careful to read your instructions with your strip kit because:
a) a little change goes a long way.
b) no one on this planet can read the teeny stamping numbers on those things.

I usually let my technician tweak the knobs.
She is that good!


One small change at a time and you can crispen this carb up real nice.
Hope the info helps.
Jeff

Originally posted by racerxjj67
I read that I could tune my Edelbrock 750cfm 4-barrel carb by hooking it up to a vacuum gauge, is this true? If so, do I hook it up to the 2 ports at the front of the carb and adjust both screws to get the best result? Also, it is recommended that my measurement should read between 15 and 20 in., but I have heavy cam and higher compression (not exactly sure what size etc.) so would I be looking at a measurement more around 10? What do I look for as far as adjusting the screws; i.e. rise or fall in vacuum readings?

Not done yet, stick with me.

Should I attach it to the manifold port, also, at the back of the manifold and check there also? Will the measuremnets be the same? It also has a pressure gauge on the dial.

Thanks again.

Thanks, but I have a couple of questions. Do I set my rpm where I want them to be while in gear or in park and do I set that by using the throttle screw? Also, there are 2 ports on the front of the carb one is higher than the other; which do I attach it to?

What's a strip kit?

P.S. I need a tech like yours

One of those two ports is carb vacuum ( vacuum at high rpm)..
The other is manifold vacuum ( vacuum at idle)..
Start it up and pull off the plug. The one that sucks at idle is the one you want to hook up to the vacuum guage.

Just leave it in park to adjust the idle mixture screws, using the vacuum guage.

Then set the finish rpm in drive (with the a/c on..if you have a/c).

A 'strip kit' is a metering rod and jet kit sold at Jeg's or Summit or your speed shop. You can adjust the fuel mixture a lot more precisely.

Hope the info helps.
Jeff

Originally posted by racerxjj67
Thanks, but I have a couple of questions. Do I set my rpm where I want them to be while in gear or in park and do I set that by using the throttle screw? Also, there are 2 ports on the front of the carb one is higher than the other; which do I attach it to?

What's a strip kit?

P.S. I need a tech like yours

Excellent information, thanks again.

But here's one more stupid question, and I should know this but alas, do both screws on the carb only adjust the carb vacuum or will one adjust the manifold vacuum. So when I attach to the carb port will I only adjust the screw that coincides with that port or will I have to adjust both. i'm assuming that when I attach to the other port I would then adjust that screw to match up with my carb setting. Am I on target with this thinking?

Does your tech like younger guys? heh, looking good man, is that your old lady? If so then tell her I say hey. hah