Any ideas why i have to hold down rave valves to get above 5k

[drake1]

My 787 in my boat will not go above 5k unless I manually hold down the raves. Sometimes it will also if I pump the throttle. This makes no sense to me. I could see having to hold them up but not down cranking the red cap down doesn't help . Anyone have any clue as to what's going on with my 787 and yes I did all normal stuff, direct fuel, rebuilt carbs with OEM and replaced the water regulator valve

 

[mikidymac]

This has been coming up a few times this season. The consensus is that some engines need the newer "slotted" raves that was actually part of an old service bulletin or they will not get above 5000 rpm.

There is no real smoking gun as to why some engines are fine without the slotted raves and why some need them.

I would pull yours and see if they are smooth or slotted on the bottom.

 

[drake1]

Do the raves get sucked down or raise up in higher rpm?

 

[Sportster-2001-951C-Stock]

Do the raves get sucked down or raise up in higher rpm?

They move up, to expose the full diameter of the exhaust port.

My suspicion is there's not enough fuel but too much fuel will also limit WOT. Does the engine seem to hesitate as if it's lean or load up and maybe 4-stroke as if it's rich? Does applying choke improve or make the symptom worse?

If it runs away on the trailer, pull the choke to stop it assuming the stop button won't. Some might advise the idle speed is set too high, but my experience if this happens is it's too lean for whatever reason.

 

[drake1]

Can the high speed needle wear? I agree the it seems fuel related but both carbs are set to factory setting will I burn a piston opening the high speed needle more then 1/8 open as the manual says, currently its closed. I will try and do a plug test to see if the can narrow it down to at least which cylinder is causing the issue just seem odd of having to close the raves to get above 5k and leaving the cap off it so there all the way up it will only get to 4200, seems opposite of what they should be doing

 

[Sportster-2001-951C-Stock]

Opening the high speed needle will add fuel. Pistons tend to burn from not having enough fuel. Keep in mind, the factory settings should work very well so if you need to deviate, there could be a problem. It's better to solve a problem's root cause than cover it up.

That said, our fuel has changed from what it was when the factory worked out the tune.