Holley tuning

[6cougar8]

Need to know which direction on jets to go with a holley 600 double pump on a mild 351w. It had 60 in front and 68 in the rear. Put 64's in the front and in runs better. Pulled a plug and it was a light grey. Put in 68's and the plug is now a medium grey. Used to w/lead gas a white plug was normal, but w/out leaded gas I've been told that a tan plug is normal and white to gray is lean. So do I need to up the front jets to 70 or drop em back down?

Don't have a clue what the plugs looked like w/60's.

Thanks for any and all help.

 

[thehueypilot]

I have 71 front and 80 rear after coming off the chassis dyno with a 12.8:1 air fuel ratio with a 6k pull. Mine was jetted way richer (+8 front & back) with bright white plugs (Way Lean) and I thought I was running way lean. I went to a cooler plug (2 steps cooler) and the normal brown color came back. The only way to know for sure is from a wideband oxygen sensor, but you can keep doing trial and error until you get close. Good Luck

 

[taylor4g63]

I would just buy a a/f gauge. I found a used one on ebay with acual numbers (not just the lean/rich/stoich crap) for around $100. It may be a little more up front, but its alot more accurate and no more reading plugs...

 

[2bav8]

http://www.dragstuff.com/techarticles/reading-spark-plugs.html
http://cochise.uia.net/pkelley2/sparkplugreading.html
http://www.bob2000.com/carb.htm

I've found these websites pretty helpful.
Short story, don't look at the porcelin, look at the base ring for your jetting.

If you don't mind spending the money, buy a Holley Jet kit ($40). I found an interesting way to find the best primary jetting for my 347. Started out with stock jets and reduced the primary jets two steps at a time. Finally found the lean spot, and jetted it up two from there. Never thought I'd be using 64 jets in a 650 Holley but that's what it likes. Now I need an 02 sensor to back up my findings. Secondaries are best dialed in at the track or on a dyno IMO.

 

[6cougar8]

Thank you all very much.

Now I know how to read the plugs. Always thought you just looked at the ground strap.

With that in mind I think I have it jetted to rich and to hot of a plug.