adjusting richness of fuel air mixture

[GordonBH]

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

[GordonBH]

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

[V8Bikers]

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.

[GordonBH]

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.

[V-MAN]

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.