I'm still thinking lean too. Maybe the fuel in the carb bowls is getting low at wot, maybe fuel filter restricting too much at high speed?

Thanks guys ... plug on right is the new motor. Plug on left backfiring motor(port) . The new motor (starboard) is definitely lean .. Port motor is ok (not lean) ...antway putting in new fuel filters and might go ahead and check compression ....As much as it pains me to pull all the plugs but guess I should .

Mike, you running the stock Merc fuel/water seperator filters????? If so, consider swapping them out to the Racorp units with the drain plug. They filter down much farther than the stock Merc units do.

I swear on my screen it looks like the plug on the left is carboned up badly.

Here it is lightened up a lot. Pic doesn't look pretty but you can see color on the tips better.

I noticed they are different plugs too. Maybe NGK on the left and Champion on the right??

Could the fuel lines on the suction side be old and soft, and collapsing at wot?

Scares the hell outa me to think the fuel line could be collapsing But I'll check em .... Using Formula31's link ...
http://dragstuff.com/techarticles/h...read-plugs.html

The plugs aren't that bad per that website ....

Mine are Stock ... use these ? http://www.marinefilters.com/product...ber=W320RRAC01

Has 3 ports ... one in two out ? 90 GPM ..guess you could use just one ?

No mine are not "see thru". I'll get up in the boat today and post the model # here.

I had several racers and "big boys" recommend these. They also recommended draining them after every run, or every other run, unless you have a problem. You can also buy the filters only which just replace the originals in the cannister. Everyone swears by them.

Also, be aware if you are running mechanical fuel pumps they won't fit in the stock location, as the Racorps are taller. I had SS couplings made up which bolted up to the posts that the stock bracket bolts up to. Then I just bolted the bracket to the end of the couplings. Worked great, but the spacers cost me two bills.

Cheesh, I forgot that picture was before I cleaned up the engine compartment and repainted the pulleys. Looks bad. But you can clearly see the spacers I'm talking about.

Mike, the Racorp units I'm using are: S 322 OUL Russ

Do those screw onto the existing fuel filter mounts? ( with the offsets of course)