Why did you have your computers reprogrammed. Did you do this because of your new exhaust?

JT,There's got to one closer than New Orleans.Ask a local speed shop or carb shop BUT,if you strike out give me a call 1.504.486.7070 weekdays and I'll hook you up.Good luck,BOB

I tuliped an exhaust valve on my starboard engine (#6 cylinder) and when I checked the jetting on the rear carb I discovered that the 'genius' that recalibrated the carb had left a bit of the gasket from the bowl floating around. Guess where it ended up..... that's right..... in the main jet to the venturi right over the #6 cylinder. But to have both of your #6 cylinders pistons damaged leads me to believe that it is an 'engine management' issue. Ie: fuel injection system too lean for that hot running cylinder and or too much advance or a combination of all those things. Although the fuel and air mixture went through the blower and then into a plenum before it went into the intake runner. I have to wonder how much the restricted jet added to the burned valve. After it was repaired I didn't do any rejetting but never had the problem again. I was very careful to check the plugs after that happened though. My jetting for the engine was on the rich side to begin with. Good luck guys.

How do the other piston look? Is there any pitting on the outside above the rings? How do the rings look? Are they missing any of the finish?
How many RPM's do you run at WOT? Do you run WOT for a long time? Some EFI's Rev limiters cut fuel and can cause the engine to lean out, and if the engine is held at WOT bouncing off the Rev limiter detination can burn the pistons.

With the modifications you have done on these motors, they will want more fuel. You might want to check if the boat has anti-siphon valves. They can be very restictive.

Have taken motors down further, have problems with # 6 cylinder gold color top of piston warping, bottom of all pistons in both motors show signs of heat , gold color. I think I was running WOT on rev limiters, could this been leaning out ?:confused: :confused:

I'm no computer guru by any stretch, but I've been told that early (mefi3)? controllers leaned out the mixture instead of adjusting timing when on the rev Lim. . If so that may be your problem. and if so, what a dumb way to slow down a motor.

Dan

Going with the last modification......Are you running a restrictor in the T-stat housing? T-stat and Bypass hose? With no restrictors of any kind, WP will be low. Not enough for a good fill causing the rear cyls. to run hotter. Low WP can cause for steam pockets in rear of heads.
My feelings are a WP gauge is a must whenever a crossover is used. No if, ands or buts about it. ;) You have to know what you have.

Iam running a 120 T-stat and a by pas hose, but no WP Gages. Iam thinking about adding Water prasure gages and fuel preasure gages. Which ones are the most important:confused:

They both are.... trick answer for a trick question :p