I had my motor rebuilt, high-pressure fuel pump rebuilt injectors sent off and professionally cleaned. My mechanic says it will idle great while trimmed up but as soon as he trims down it sputters and dies. He’s scratching his head.

Does it have a low pressure pump that feeds the VST ? If so, the VST is kinda like a BIG float bowl on a carburetor. Maybe the VST tank isn’t filling properly and causing a fuel starving issue when it is at a certain angle?

IDK. Just a thought.

Yes, not knowing the exact model it should have two low-pressure fuel pumps that go bad over time and should be repaired or replaced (replacement cost is not to bad)

The best person that posts on the web for Yamaha and HPDI is guy RodBolt on https://forums.iboats.com/

Lots of info on the web https://www.youtube.com/watch?v=Pb1gC2WOErU

My SHO has done the same thing for 800 hours. Always have to trim it up a touch when idling. Know of multiple Yamahas that do that. Both 2 and 4 strokes. I just assumed they don't like to be buried at forward idle.

Those pumps are extremely inexpensive to repair and are very easy too. Basically they are tiny diaphragms that pulse through a checkvalve. The pulses are created by internal crankcase pressures.

Do you smell raw fuel at times?

i had the same problem on my 300hpdi new pistons both low pressure pumps new vst new high pres pump injectors cleaned 3 times new coils plugs new fuel lines and primer bulb it would run fine on a hose but put it in the water and it would die so a year later and wasted 1600 dollars on it my skeeter now has a new 300 pro xs v8 on it i just wish i would have put it on first and just sold the vmax but the four stroke is awesome

When i got my bug; a 2012 model, the 200 sho probably had all the orginal filters with 147 hours on the clock. The first trip out it was dropping cylinders under full throttle so I limped it back to the trailer and brought it home and changed all the filters but the VST filters. I put a can of Sea Foam in each tank and put a little in one of the filters when I changed it.. It also had about an 1/8 of a tank in each tank of really stale fuel. I added about half a tank each of fresh fuel unfortunately the kind with ethanol. It ran a lot better but when I'd back out of it and re-excellerate it would still drop cylinders after a long run. I finally found a source for no ethanol fuel and started filling it up with that, on the first fill up I added a can of Berryman B12 Chem Tool to both tanks. Berryman will desolve varnish and pretty much any contaminent that isn't a solid. I have the filters for the VST and will change them this winter; there is videos on you tube on how to do this in detail. My bug runs like a top with the fuel system flushed out and good fuel. Working in the auto industry and being a mechanic back when there were carburators on everything and gummed up was regular happening Berryman was a life saver.

Everyone talks about seafoam. B12 is about the best stuff money can buy to clean your system up

Easy thing to check - Make sure your fuel line isn't getting caught in the lower trim angles and getting kinked!

Is it hard to start also in the down position ? I like Scott have a 300 that is like yours and his. Some have question whether it could be the turner having to much back pressue: check with yammy 911 on BBC.

Appreciate all the info guys. He was going to clean VST tank and filter and put the new LPfuel pumps on this weekend to see if that corrects the issue.

It will fix it. I’m pretty sure

Was also told to do a link an sync. Is that something that needs a computer to do.

Heard back from mechanic. Checked LP FUEL pumps they were good. Said only runs on 4 cylinders in forward but all 6 in rev. His Yamaha software bit the dust for his computer so have to wait until new software comes in.

on my 300, after it was rebuilt, had to take it to have the TPS adjusted correctly. It was a smidgen (technical term for .00000000000000005mm) off. It made a world of difference being just a smidgen off.