Engine runs great CO 3,5% idle spark plugs are black

[HKZ Bob]

Do I have to worry and change my 911 MFI 2.4 setup?

What is your experience on your platin bosch plugs.
I don't want to run my engine lean. this causes overheat. Where to find the the best compromise.

Pictures of your plugs could help


Bob

[304065]

Bob,

Platinum Bosch plugs are not recommended based on long historical experience. The NGK plugs, such as the BP7ES or BP8ES, are better, and much less expensive at under $2 each.

Actually, overheating can be caused by an excessively rich fuel mixture as well. You say you have 3.5% CO at idle, what about at part-throttle? Most of us experience 5-6% at idle and 7-8% at part throttle under load, using a wideband exhaust sensor system such as the LM-1.

It's entirely possible that your idle CO is low but the pump is much richer on part throttle, hence the black plugs. Check measure adjust requires that you investigate all the possibilities before adjusting the mixture-- download a copy here and perform each step before making any adjustments.

Good luck!

[john walker's workshop]

bosch platinums suck. i tend to run a hotter plug in rich running situations, like MFI or carbed hot rods. bosch heat ranges get higher the larger the number, NGK is hotter the smaller the number, basically. i don't think spark plug charts have ever been changed since the 60s/70s when gas was good and tailpipes were white, so you have to use some discretion when choosing plugs. and yes, you probably don't have very good transition with 3.5% idle CO, and you probably need to set idle and midrange as previously mentioned on a gas machine.

[kach22i]

Originally Posted by john walker's workshop

bosch platinums suck..

Took the words out of my mouth.

My old plugs...............
Best spark plugs to use? Hi-tec or Standard?