Originally Posted by spareparts
good solid engines, basic efi. They like gas though. If you want to get ahead of the curve and get it all ready for next season. Plan on doing some off season maintenance to them. O2 sensors are easy to clean, remove from housing, heat till cherry red with a map torch, let cool off and reinstall. Make sure to clean the passage into the cylinder and the little barbell thing with merc power tune or parts cleaner of your choice. Yamaha sells the gaskets needed as a kit. Replace thermostats, be care full, those little bolts break off easy. Replace water pump impeller, use yamaha factory kits only. If it doesn't have a water separating filter for each engine, install one(new fuel hose doesn't hurt). If you're up for it, take the vst(fuel tank assembly on the engine) apart, clean it out, replace the screen on the fuel pump. While its off, check or replace the mechanical fuel pumps. Tighten the bolts holding the pumps together, there are three of them. If you think you need diaphragms, check the price on the whole assembly, they're not much more than the rebuild kits. Run good fuel, good oil and ring free and you should have good service out of them. Items of note, they only run on four cylinders at idle, so don't get freaked out of it seems like they aren't hitting on all 6, they aren't. Trim motors and fuel pumps are very expensive from yamaha, the aftermarket is supplying good alternatives for them now.
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