Need help setting carb/tuning

Reply Subscribe

Thread Tools

Search this Thread

Aug 9, 2007 | 10:28 PM

bmankin

Thread Starter

Advanced

Joined: Sep 2004

Posts: 87

Likes: 0

From: TN

Need help setting carb/tuning

I am trying to set the idle mix on a carb. I have two different tachometers. One on a nice timing light and the other on a digital multimeter. The problem I am having is that the engine sounds smooth but both of the tachometers are running up and down to the point I have no idea what the actual idle is. It seems to vary as much as 100 RPM just sitting there idling. Is there some way to filter that? It moves to fast to average it and there doesn't seem to be a true peak. I think I need something with a needle on it.

Aug 9, 2007 | 10:31 PM

SIXFOOTER

Le Mans Master

Joined: Jan 2006

Posts: 9,192

Likes: 27

From: Boca Raton Florida

Is the engine speed actually changing or is it just the tach?

Aug 9, 2007 | 10:43 PM

bmankin

Thread Starter

Advanced

Joined: Sep 2004

Posts: 87

Likes: 0

From: TN

Quote:

Originally Posted by SIXFOOTER

Is the engine speed actually changing or is it just the tach?

It appears to be just the tach but both tachs act the same. The engine sound smooth to me.

Aug 9, 2007 | 10:51 PM

Tim H

Safety Car

Joined: Oct 2000

Posts: 3,593

Likes: 103

From: Southern Indiana

Either add a thrid tach for 3Xs the problems or trust one and go with it.
Put your car in gear and read it, go for a spin and read again.

Aug 9, 2007 | 10:55 PM

bmankin

Thread Starter

Advanced

Joined: Sep 2004

Posts: 87

Likes: 0

From: TN

Quote:

Originally Posted by Tim H

Either add a thrid tach for 3Xs the problems or trust one and go with it.
Put your car in gear and read it, go for a spin and read again.

Its not that it is reading wrong. The problem is that it fluctuates so bad I can't set my carb.

Aug 10, 2007 | 06:07 AM

BarryK

Le Mans Master

Joined: Apr 2004

Posts: 7,106

Likes: 38

From: Newark DE

don't use a tech to set the carb if you are having this problem, to be more accurate, use a vacuum gauge hooked to full manifold vacuum and adjust idle mixture to achieve the highest steady vacuum reading.

Aug 10, 2007 | 09:03 AM

Tim H

Safety Car

Joined: Oct 2000

Posts: 3,593

Likes: 103

From: Southern Indiana

Your tach is either at fault or you have a huge miss.
Even a huge lopey cam won't flucuate the idle the tach reads.

Aug 10, 2007 | 01:04 PM

LXXVIII

Heel & Toe

Joined: Nov 2006

Posts: 16

Likes: 0

From: Atlanta Georgia

Do you have an MSD box? Using a stock tach with an MSD will cause the tach to act irratically. If you are using an MSD box, plug the tach into the box instead of the coil...

Corvette Stories

The Best of Corvette for Corvette Enthusiasts

Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!

Joe Kucinski

150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter

Joe Kucinski

8 Coolest Corvette Pace Cars (and Replicas) of All Time

Verdad Gallardo

Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)

Joe Kucinski

Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!

Verdad Gallardo

Top 10 Corvettes Coming to Mecum Indy 2026!

Brett Foote

Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!

Michael S. Palmer

10 Revolutionary 'Corvette Firsts' Most People Don't Know

Joe Kucinski

5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2

Michael S. Palmer

2027 Corvette vs The World: Every C8 vs Its Closest Competitor

Joe Kucinski

Aug 10, 2007 | 05:05 PM

bmankin

Thread Starter

Advanced

Joined: Sep 2004

Posts: 87

Likes: 0

From: TN

Quote:

Originally Posted by LXXVIII

Do you have an MSD box? Using a stock tach with an MSD will cause the tach to act irratically. If you are using an MSD box, plug the tach into the box instead of the coil...

I have the MSD Ultimate HEI Kit. The odd thing is one of the tachs plug into the distributer and the other is inductive. The tach on the dash is as smooth as butter. I think I'm going to do the vacuum thing and quit stressing.

Reply Subscribe