Reading plugs in a gas motor? Is it the same?

Im comfortable reading my plugs, its my most trusted tool to tune a motor...But, I have a buddy that wants my help to setup a motor in a whole different world to me. Its a procharged 540 BBC on pump gas...in a boat....brand new build, maybe 20 minutes run time..

I looked at his plugs and no cad is burnt off the face of the plug, just the ground strap.

He is running wideband O2 sensors (1 per side) and his gauge is reading 11.5-12.0 to 1 AFR, which if I were to trust those I'd say he is getting close but still a bit rich...

Right now the timing is at 28* which sounds like a bunch to me... I told him the next time out we would back the timing off a bit and start pulling fuel until we see burnt cad.

Im a little out of my comfort zone here, and not sure what to look for in a pump gas motor.

Any help or ideas would be appreciated.

 

What brand of spark plug ?

 

On unleaded pump gas, or even racing gas, you can get kind of close by looking at cad, but the amount of run time you had on them will be tough to determine anything if the motor wasn't shut off immediately after being under wide open load. Gas engines shouldn't be burning the cad off, but rather leaving a soot ring. So you don't want to brake clean them to read right away. Mostly gray with a little ring of black is about perfect on there. The fuel ring on the porcelain is always the sure fire way to see. It needs to be a beige/off-white color since it's pump gas(unleaded).

Have to watch plug heat.. discoloring should be consistent halfway down the ground strap or so. That's typically where you should only see smoked cad is on the ground strap. Just like with alky, timing and fuel can trick heat too..

That being said, 12.0 is pretty safe. It's really easy to detonate with a blower and gas, so watch pulling fuel, it will go lean quick.

 

And the fuel ring to read is at the very bottom of the porcelain. If you keep the heat mark on the ground strap in the middle of the bend it will be safe for timing.

You don't read them like an alcohol plug. Gas has a much narrower tuning window and pump gas is even narrower.

Mike Canter has a good article on gas plug reading. Type his name along with plug reading 101.

Blessings.........Ron

 

They are NGK-8's.

Ok, soot ring on porcelain... a narrow black ring then off white or beige. I will have to have him run a new set for another pull and have a look to see where we are now.

Thanks.

 

Off/white beige at the base/bottom of the porcelain inside the case to read WOT. Hard to see without a scope. The soot ring you look for will be in the same place on the bottom of the threads where we normally look to see where we burn the cad.

 

Follow Mike Canters instructions and you will get it. I run a blown gas engine at 40 psi and it's happy and Mike is right on how to read them for gas. He also has one for alcohol if interested.
http://www.mindsciencemotorsports.com/graphics/PLUG TECH.htm

Blessings........Ron