I have a warmed over ZZ502 that keeps fowling the spark plugs. Although jetting is pretty good. It also seems to only fowl one plug on the driver side front.

The motor is a ZZ502 with Cometic head gaskets, crane roller rockers, and a merc HP500EFI cam. The compression on my snap-on gauge is about 170psi, maybe a slight bit more ( like 175 ). The motor runs great.... except for the fowling. I can only get 91 octane gas.

The plugs are NGK R5671A-7 they say V-Power 7 on them.

Any help?, I cannot get ahold of my engine guy here..... think he is on holidays.

Thanks

RT

well... i usually use a 410 w/ bird shot... oh sorry... wrong fouling...

in your case would suggest not a plug issue at all... if was would be all 8... suggest if efi, then you have a bad injector or if carb any number of things from a single bad spark plug wire and any number of issues like that or maybe a bad valve guide that oils it up... either way... if other plugs look ok then is a specific cylinder related issue... not a sparkplug issue

first thing i would do is swap a spark plug wire and see if the problem moves w/ the wire... easy and quick

#7 is as warm as I'd go in that motor.

Make sure float levels are good and then set your idle circuits to get max vacuum then go 1/8 to 1/4 turn out.

Then make sure you have the correct power valves, about half of idle vacuum is a good starting point.

Damn, I was hoping you guys were gonna tell me to put 8 heat range in.
To be fair, I cannot be 100% certain that it is just one plug. But is is on the driver side. There is mild popping coming up on plane. And the boat is down on power. Change the plugs and it all back to normal....... for awhile.

RT

8 is cooler than 7 http://www.ngksparkplugs.com/techinf...000&country=US

you either have an ignition problem or a fuel problem if you you are not using oil.

An MSD type ignition would help, I run #9 plugs and still don't foul them.

Never thought of the MSD.
The motor was set up on a Active engines dyno in toronto, and final jetting in the boat.
I know that they are keeping it fatish to make it live.

What MSD do you reccomend?, The ignition is off the old 330.

Thanks

RT

First, I'd still get a vacuum gauge and check the idle circuits and power valves, dyno operators rarely set idle mixture properly due to the added drag from the outdrive, they just want it to run, same with the power valves, most times they are looking at WOT mixture and not primary versus secondary mixture and whether the power valves stay closed at idle.

The popping you mentioned could have blown a power valve also.

MSD 6M is the right box, there are other choices with your ignition

The popping is from the exhaust side, not the intake. One thing intersting is that it seems to be worse on plugs in the warmer weather. Then in the spring when we put it in for the fisrt time.
I will get that looked at..... the vacuum.
Please tell me more about the ignition.

RT