Sorry for the long winded prelude. I have a 1992 Chappral with the Yamaha 4.3L. Before taking on first trip this summer, I replaced plugs, plug wires, distributor cap and button, coil, coil wire, fuel water seperator, and oil filter and oil. Did not check my timing which I believe may be the problem. Beging of season's first trip, the boat ran better than it ever has. After about two hours on the water, the tach dropped from 4,600 to about 4,000. I dropped back to idol and could hear a definate skip. I continued on our way, hoping maybe a it would clear it self out. After another five minutes it dropped again from 4,000 down to 3,300 and the boat stopped plaining. Relizing I had a definate problem, we headed back to the dock. 3 min. later the motor quit completly as if the key had been turned off. .....Back at the house, I removed the sparkplugs and found the ends complely melted off of 1 2 and 3. I did a compression check and the results were as follows,<br />cly. <br />1 0 psi<br />2 10 psi<br />3 15 psi<br />4 120 psi<br />5 118 psi<br />6 was so pissed off didn't bother.<br />I removed the heads and found the intake valves collapsed on 1 2 and 3 and starting to on 4 5 and 6. I talked to my dealership and had them examine the motor for a cause. They said the 4 possible causes for detination are: timming off, running rich, clogged exhaust system and running hot. According to the temp guage it was running between 140 and 160 (and it is working). What confuses me, and them, is how it went that wrong in less then 2 hours of run time (and part of the time was spent swimming and just idoling around). I checked my exhaust manifolds and there is some build up in them but they are still pretty open. No rust, just gunk buildup. There was also very little if any carbon build up in the cylinders. I plan to rebuild the motor myself, but want to find and fix the problem, not just the effects. Any input is appreciated!!
<br />can and do add up to failure.<br /><br />Is the dealer helping? are they going to<br />inspect and determine cause?<br />Will they makes changes or upgrade when<br />repairing. <br />Hope you figure it out.<br />Please post back when you do,<br />Good luck