200 HPDI 3.3L Surging at WOT & Only 5,000 rpm's

[CGWright]

I noticed in Kentucky that it wouldn't run WOT like normal, only able to get about 62mph @ 5,000 rpm's. (Now I ate a lot at the rally, but not THAT much. )

Today I did some more running to double check and the motor is surging at WOT, 61-62mph @ 5,000 rpm's.

The water filter was changed last fall, and the plugs are last year's.

Holeshot seems to be a little slower, and rpm's at about 3000 versus 3500 rpm's before.

It sure feels like a fuel delivery problem to me, but I wanted to get some others' thoughts.

[CGWright]

Anybody?

[dward51]

Well since it's a HPDI, the usual suspect in a fuel delivery issue is the VST filter. Have you removed it to check and/or clean it yet? Also depending on how many hours you have on the engine there is a medium pressure fuel filter just after the VST unit that can clog, but 9 times out of 10 it's the VST.

Here are a couple of links to "how to clean VST filters" on several sites. Some are for different Yamaha engines and may show parts on different areas of the motor, but the proceedure is the same (some have better photos than other too). You may want to make sure you have a VST gasket and extra filter on hand in case you tear the gasket or filter, but you can often just clean and reuse the old one:

http://www.bogueinletnc.com/yamaha/8.html

http://www.thehulltruth.com/sh....html

http://www.tidalfish.com/forum...ilter

http://www.thehulltruth.com/bo....html

[CGWright]

Thank you, that's some good info!

[Rich Z]

Replace the fuel strainer just above the vst on fuel pump output hose.
http://www.bbcboards.net/zerothread?id=319634