Rpm drop off at wot 150 xp

"I have a 1990 150 xp model ve

"I have a 1990 150 xp model ve150 slesb. at wot the rpm falls from 5400 to 4800 after a few minutes of run. I have changed pwr pack, stator, reg/rect. coils, plug and wires at the reccomendations of local marine tech. compression is 84-90psi and leak down is 10% or less. spark checks good at idle on hose. help"

"Brad, obviously not an igniti

"Brad, obviously not an ignition problem, unless you are losing spark at high speed - hopefully you kept the old parts as spares.

You may be getting air in your fuel system, or have a clog/blockage somewhere in the lines.

I would check any filters/water separators - clean and replace if necessary.

If you are running off a built-in gas tank, you could try a portable. That would quickly tell you if the problem lies in the tank (pick-up, crud in the tank, bad line, anti-siphon valve etc).

Best to grab a manual and go through the troubleshooting proceedures outlined. Don't replace any more parts until you can confirm that they are bad...."

"graham thanks for the quick r

"graham thanks for the quick reply. i have the manual and have gone thru the procedures. everything checks to specs. rebuilt carbs, new vro, antisiphon removed for now all new fuel lines that have been pressure and vacuum checked. pumping bulb at wot does not effect rpm. choking at wot causes momentary bog as choke is applied."

"Brad, that really is a 'h

"Brad, that really is a 'head scratcher' - sounds like you have replaced or tested everything that could potentially cause the issue."

"Brad, have you tried running

"Brad, have you tried running the engine with the cover off to see if this makes a difference?"

"Brad, I would give Bob's

"Brad, I would give Bob's idea a try. I have been thinking over your issue as well.

Can you cause this issue if you leave the boat on the trailer and simply run the motor submerged normally, but not underway (like on a boat ramp).

Bob is suggesting maybe it is starving for air - so definately check that out, good bit of troubleshooting there.

I was trying to think of external factors (extra drag after initial ventilation) that could account for the 600 rpm loss."

I will try to run without engi

I will try to run without engine cowling. It does not seem to appear on the trailer. I was wondering about the timer base If i can locate one could this be breaking down with load/temp. Also if i do change this i would like to verify wot timing setting at 28*?