Z06vette1

I have a 7.4 mpi is a 200 baja h2x that was rebuilt this year. While pulling the plugs to spray some fogging oil I noticed the starboard rear plug was black and looked like it was dry fouled and I was able to scrape some carbon off it the rear port plug looked like it was new it was dry and the electrode was completely white and clean the other 6 plugs had a nice brown color to them I put about 75 hours on the boat this season and it ran great other than being a little lazy in the 4000 plus rpm range that I attributes to possibly being over propped it has a 23 pitch mirage plus. Is this something I need to investigate further? Any ideas?

dbkski

iTrader: (1)

Yes you should be concerned.
Yes you should investigate further.
Yes you are over propped.
Try the simple things first.
Engine rebuilt how? Stock or did you add HP?

My 1999 7.4L MPI used an AC MR43LTS plug gapped at .045".
My two boats that had 7.4L engines came with 21P Mirage
Plus props and were similar in size and weight as your H2X.
Lugging your engine is not ideal.

Replace the bad plug. Clean and re-gap the others. Do some
test runs and check the plugs, wires, cap, rotor and all their
connections.

Z06vette1

The rebuild was done completely stock, new bearing rings and a complete head job with new valves etc, the 23 p mirage plus is what came with the boat from the factory will be looking to either have it labbed or will try a 21 p in the spring. A new cap and rotor was placed when the rebuild was done, it seemed to run fine and the plugs issue wasn't discovered until I winterized the boat. I'll replace the plugs in the spring it currently has the ngk 6brefs gapped at .45 the other issue I noticed is that it has a k and n air cleaner that the boat cam with and it looks incredibly dirty, I'll be cleaning it in the spring or just replacing it with a stock unit. This boat has been a big project this season and I hope to get it running at 100%. How often do the plug wires need to be replaced in the marine application? They are about the last thing that hasn't been replaced on boat

Thanks

Larry

dbkski

iTrader: (1)

6brefs?
No such animal that I can find. The plug I referenced above
crosses to NGK BPR6EFS. Check your plug number.

If you can't pinpoint the last time you changed your plug wires
then it is time to replace them.

Cold weather, dirty air cleaner/filter, or a faulty sensor will
make your engine run "fat" thus leaving deposits on the plugs.
However seeing that only one plug is messed up I would look
there first. Plug, plug wire/all electrical to that cylinder, or a
dirty injector may be the cause. Start looking.