I have a Yamaha 1989 40hp oil injection engine, 2 stroke, on a 13 sport boston whaler. Last season I had water in my fuel, wreaking havoc on my engine, i shelled out some cash to a mechanic to get it running again, but the entire season I seemed to have problems similar to the watery gas, but no water. My symptoms consisted of mostly engine stalling at low/idle speeds, and at high speeds, if the throttle was wide open, it would run smoothly, then the revs would drop as if i unplugged the gas line (which I didn't). Variations on this problem occured all season long, sometimes I could get it running again after priming the feul line bulb, sometimes not. I went through a new feul/water seperator, 3 new complete carbs, countless hoses and fittings, a new portable tank (I suspected my old one of leaking water), and at the end of last season my mechanic informed me that my issue was with a cracked ignition coil that was arcing and would not spark the plug - he replaced that, and it ran for an hour or so before I put it away for the season, i figured it was fixed, at last (it was november by the time it was finished). This spring I ran it with the flushing ears and the hose, with a new tank and feul line and gas from a new land station, and it idled fine for about 30 minutes, for two different sessions. <br /><br />I put it in the water in early june, about a month after running it last, and I had the about similar problems with the dropping revs. However, I can attain flawless performance so long as I squeeze the primer bulb during operation, becuase it does not remain firm on its own. After this, I tried adjusting the carb idle mix screw, with no luck, and decided that there was a good chance my feul pump was shot. I thought the diaphragm might be weak/punctured, according to the shop manual i have. I installed the new pump, ran the engine, and now began to have the opposite problem - it was not being feul starved, it was being air starved. I thought with the new pump feeding a new amount of gas into the engine, more air was needed. It was, after I adjusted the screw for a leaner mixture. It ran beautifully for about 3 hours, and i thought i had the problems in the past. The new pump kept the primer bulb firm, and provided a constant flow of feul.<br /><br />Later that night I ran it again, but the engine regressed to the old condition requiring priming of the bulb - it would no longer stay firm on its own. Dissasembly of the old pump did not reveal any punctures in the diaphragm on visual inspection, which was odd considering the cure of my problems for a few hours seemed to be the new feul pump. <br /><br />I decided to re-adjust the mixture screws on the carbs, but no luck. I noticed that After backing the screws all the way out in half-turn incrememnts, and seating them all the way in, I could not recreate the problems that i had when i first installed the new pump - the apparent flooding condition. This leads me to possibly believe something has damaged my pump, which also would explain why it worked for a few hours and then suddenly stopped working. <br /><br />I checked all the components of my feul system: the tank, primer bulb and feul line, fittings, are all brand new; i cleaned the feul filter; the pump has just been replaced, the carbs were replaced last season with very low hours on them. I have yet to check the internal lines for clogs, but i doubt that is the reason.<br /><br />I also tried cleaning my carbs, suspecting varnish deposits on the needle valves from possibly old/stale gasoline, and the valves would stick closed and wouldn't return after the bowl of gas was emptied. No luck with that either. <br /><br />So basically, I have two questions: has anyone heard of such a problem before, and if so, any solutions? Also, in my shop manual it described the diaphragm as being possibly damaged from engine backfire, creating too much pressure from the crankcase. I havent heard any backfires, but is it possible the crankcase is creating too much pressure, damaging the diaphragm after only a few hours, or could the opposite be true, that its not creating enough of a pressure difference to draw gasoline?<br /><br />Any possible advice would be greatly appreciated, this engine never suck me dry of ideas, or of cash flow. Not to mention i'd like a fully funtional engine. <br /><br />PS- This is now my fourth summer with this engine, and last season was the first time it gave me any hint of an issue. Even now, forced to prime the bulb as I drive, I still love the performance and smoothness of this engine.
