Run on



OK, I have been runnin the stang for about 5 months without looking at the plugs. I was getting some run on lately, so I removed the plugs and I had some carbon build-up on them. My ignition system is working properly MSD everything, DII, 10* advance. I am using autolite plugs that I got over the counter. I assume stock heat range. My question is, should I go with a hotter plug? and if so what temp range?

Thanks guys!


Depending on how bad the carbon buildup was may or may not have been the source of your run-on. You may have your idle speed set too high, or you may have the timing set too far advanced (you say 10*, but the balancer DOES slip and throw the reading off). Do you hear any ping or rattle from the engine on hard acceleration? That would indicate too much timing advance.

Hotter plugs are good to prevent oil fouling but not carbon fouling. Carbon is rather resistent to the higher temps or combustion unlike oil. With your COMP cam and if you are over 9:1 compression, I would recommend an Autolite 45 plug - one step colder than stock.

You might run a good de-carbonizer through the engine though. Sticking a small vacuum line into a cup of water while the engine is running works rather well to "steam clean" that carbon out of the chambers.
Ya, i went and checked my balancer and it is right on. The grooves on both the hub and the pulley are lined up, the idle speed is set a 650 rpm. I'll try to get some decarbonizer tomorrow. Otherwise I will try the water in injection method. Is there any difference with carbon build-up if I use a higher octane fuel rather than just 89? I usually don't get any ping with 89 octane unless it is really hot outside. But usually I run around 93 octane or so.

Thanks for your help!