2005 Yamaha 300 VMAX HPDI Surging issue

[417farmallfg]

Engine idles well, but anything above 1300rpm, engine surges and will not plane out
Does anyone have a service manual or ideas as to what would cause this issue?

[Bass1980]

Sorry I'm not knowledgeable in marine motors but I had a friend with a mercury that just had the same issue. All it ended up was the spark plugs was dirty. Gradually his hole shot got worse and worse until couldn't plane anymore. Cleaned spark plugs and now hole shot is normal. Just something to think about. Good luck. I too have a 300 hpdi so I'm interested in what you find out.

[Brianmoore25]

Check basics first. Firing, compression,fuel quality. Then check lift pumps,fuel pressure from VST. If you have access to diagnostics software you can check high fuel pressure. If VST pressure is good I'm betting you'll see a drop in high pressure when problem occurs. If that happens it could be the filter between VST and high pressure fuel pump or also the basket filters in high pressure pump.

[21XDC]

Could be a weak battery/low voltage/loose or dirty contact issue......