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Hi all,

In England we have a test I have to get my 07 SB SS through, it means my CO% must be under 4.5%. My local wrench adjusted the Holley to 3.8 both sides. I am told that's too lean for safety by a guy who really knows his stuff.

I'll re-set it for the test to 4.4% and pray, then I intend to richen it up - I intend using the Colortune plug system in 14mm plug size is that OK to use? I have read about the plug being taper seated - any potential damage possible?

If so, what is the recommended CO percentage? and I'll have to do it with a gas analyzer.

Gordon

Sorry team,

This should be in Tech, I can't do it but if anyone wants to move it, great.

Somehow, I don't think this board will whip my butt for it. but to keep it on topic which idle mix screws (4 of) affect which cylinders?

Cheers Gordon

Hi Gordon,
no butt whipping here I moved this over to tech for you. I am not familiar with colortune or adjusting the CO. Here is a link to Holley's video instruction page for tuning the carb. http://holleytv.com/?cat=13 Hopefully, a tuning guru on this board can help or perhaps contact Andy at Germany Boss Hoss or one of his mechanics can speak with your guy. Good luck with passing emissions.

Thanks V8bikers for the advice,

Great videos from the Holley TV channel. Shows it's so much easier working on a carb under a hood!

I had my local wrench adjust the front 2 in the primary metering block to get it under the test limit but he went a bit far - I'll get them back up closer to the limit to richen it a bit but want to do it properly when I get it back home post-test and don't want to do much when it could be running lean.

The colortune uses a replacement spark plug with a crystal spark plug body and allows you to see the ignition as it happens! Looks like a good set up as you can see the ignition flame color change at each adjustment and adjust to perfection (pure blue flame). Only $39 in the UK.

Gordon -

Here is something I found when looking around:

The best way to accurately set idle mixture is to use an emission-test machine to read hydrocarbon (HC) and carbon monoxide (CO) levels. As you move the idle-mixture screws, you’ll see some very dramatic changes in HC and CO readings. The ideal idle-mixture setting will minimize both the HC and CO. HC readings are expressed in parts per million (ppm) while CO is given as a percentage. One fact that is generally overlooked is that CO can be equated to air/fuel ratio. For example, 0.01 percent CO is equivalent to 14.7:1 air/fuel and 0.38 percent is equivalent to a 13:1 air/fuel ratio.

Read more: http://www.chevyhiperformance.com/howto ... z2kYUiTJGT

By reading that, I'm not sure I would fatten the carb anymore then your mech has it. Ideal for power should be somewhere between 12.8 -13.2 and he has you set at aprox 13:1 ... you are right in range for best power now.