07 70hp cutting out @ 5600

The motor is an 07 70hp and seems to runs fine until you hit the magic number of 5600 then the motor drops almost instantly and sounds like it is starving for fuel or maybe spark. I’m at a total loss on this at this point. My carbs I have been told are clean and I do not run ethanol at all in the boat. Here is a laundry list of what has been done since this gremlin reared its head:
I have replaced the anti-siphon valve 3 times.
Replaced both filters inline and fuel/water twice
New plugs
New primer bulb
Carbs re-synched and linkage adjusted
This has the mechanic scratching his head as well. He has said with the boat running he cannot find this problem or diagnose it as everything checks out just fine (fuel flow etc.) but this problem seems to persist. It only seems to happen once I get over 5500 which for me is very rare but none the less it needs to be fixed before I have major trouble. I’m at a loss on this and wondering what else is left besides possible ignition, or maybe a carb problem that wasn’t seen. Any help or direction before I lose my mind would be greatly appreciated.

[jb123]

i know some of the older models had overrev limiters..not sure about the new ones, hopefully your tech would know.

I have an older 90 and it does the same. When it cuts out does it sound like it's running on 1 cylinder?

My problem was the motor was over heating at full throttle and the sensor would cut the motor back. I don't know if that applies to newer motors, but if you've been doing some mud running, I would check the thermostat.

I ***** off the shelf and rarely use full throttle, but in the rare cases that I did, it would cruise along for about 500 mtrs and cut back. The thermostat was choked up.

No it doesn't really sound like one cylinder it just drops RPM's instantly once you get to 5600 and I don't stay in the throttle to see what happens because I don't want to lean it out and BBQ the power head. This thing has got me sideways at this point no one can diagnose the problem.

[boats.net]

That engine's operating range is 5000-6000 rpm's and rev limiter activates at about 6200 rpm's, so it shouldn't be a rev limiter. Try running on a portable gas tank and fuel hose to eliminate boat fuel system as the problem.

Thanks, that was going to be my next step tonight I have a tank I just need the hose.

have your mechanic try raising float level a little and also check tach using a shop tach that you know is reliable could be turning right rpm just showing bad tach reading but if tach ck out would raise float level as i have had them to run out of fuel at high rpm sucking bowls dryer than at lower rpm what does your plugs look like lean or rich

Plugs look great just like they should. The tach is right on, the corresponding RPM's are correct with where the speed should be and always has been. I'm starting to think it is a carb problem that no one caught at this point. I'm putting it on a seperate fuel source this evening to isolate this issue a little more. Thanks for your input every bit helps!

Just an FYI. The fuel was fine broke the carbs down to clean them again and this did nothing to fix the issue. Brought the boat to the now 3rd mechanic explained all the issues they looked at the CDI changed the timing and I'm all fixed now. Needless to say the 1st 2 mechanics just lost future business....