If you’ve searched for a solution to HPDI fuel problems, this is it. I wanted to get this on here so that if anyone ever runs into this problem they know there is an easy solution. This is an all-in-one summary of how the fuel system works and what went wrong. I have never been into one of these motors before, but everything I did was extremely straightforwards. Nothing was more than some nuts and bolts. Total cost this way - $100, total cost at Yamaha’s solution - over $1800
05’ Yamaha 200 HPDI started losing top end power. Would run fine wide open but slowly start slowing down (started 4200 then fell to 3400 RPM). Motor would run fine at certain throttle levels, but once you went above it would start bucking. It eventually got the point that I couldnt get on plane. It was odd because it idled fine and ran perfectly normal up to a certain RPM.
From reading about these motors, I found they are extremely sensitive to bad fuel. What I eventually realized this meant was any fuel. The fuel system flows in this order- Main tank - fuel/water seperator - primer bulb - on motor filter/seperator - (2) low pressure fuel pumps - VST filter and mid pressure pump - mid pressure inline canister filter - high pressure belt driven pump - fuel injectors. The crucial system that fails is small filters in the HP pump as well as injector filters (more on this later)
I took a few shot in the dark guesses at first because they would be simple, cheap fixes. I pulled apart the VST and cleaned the pick-up filter. It did have some sediment built up on it. Some seafoam and compressed air cleaned it up. Replaced mid-pressure inline filter. Still no fix. Next, I pulled the fuel rail to check filters on injectors. They looked pretty clean, so I didnt assume this to be a problems.
From here, I needed a Yamaha tech to test my HP fuel pump. The LP pump is an easy test. If you can squeeze the primer bulb and the motor picks back up, you have a bad pump. Easy fix. Always check to make