Yamaha VMAX 225 dropping RPM's

[Burton1008]

My engine will run great till I hit about 52 mph and then it will bogged down and the rpm's will drop to around 4000 and will stay. Hot foot pressed to the floor but nothing more.

It seemed to be fouling plugs very quickly less than 8-10 hrs of use

I have replaced filter on side of engine with the red float ring inside, replaced all 3 low pressure fuel pumps, changed out VST filter, cleaned small filter behind pressure regulator, had injectors professionally cleaned and flowed, cleans O2 sensor. No alarms going off.

Thought I was making progress but still doing the same thing. Can it be the high pressure fuel pump not working, pressure regulator bad, or is it a safety feature shutting down for other reasons.

 

[99yam40]

monitor the fuel pressure to see what it is doing when the problem shows up

 

[Burton1008]

Unable to take to the lake today but when testing the pressure when turning the key to the right the pressure goes up to 38-40 and holds for a few seconds then starts to drop all the way down to 20 psi. Is that what it's suppose to do or should it hold constant at the 38-40 psi.

 

[scoflaw]

Like he said...what's the pressure doing when the problem shows up ?

 

[Sea Rider]

OB could be overheating at wot and temp sensor triggering and lowering wot revs to safe 4 k if it's the safe rpm factory adjusted to ? OB is used on fresh or salt water ?

Happy Boating

 

[Burton1008]

Fresh water only. I'm replacing the impeller tomorrow. Could it be tstats or popit valve. Spelling unsure.

 

[Sea Rider]

If it's an overheat detected problem will need to remove stats, popit valve and temp sensor and troubleshoot them heating them up individually to find if are doing their homework right. Will need to know the temp specs for each component. Report if a new water pump or impeller solved the issue.

Happy Boating