Low RPM at WOT

[JohnnieVee]

1990 Mercury Mariner 90Hp, 3 cylinder, 2 stroke. Engine has a 13x17p prop.
took it to the lake and ran it to see what it would do, RPM at WOT was 3000. Boat would not plane out, checked throttle at carbs, they were wide open. Engine sounded like it was under load. took back to the house. found oil line from oil pump off at the fuel pump, mumbled a few choice words, checked compression, all cylinders were at 130#.
Now the Question...... with that line coming off, would the fuel pump suck air from that port and not allow the engine to get to full RPM?
I did rebuild all 3 carbs and synced, checked reeds and they looked good, no deformity or discoloration, replaced plugs and fuel filter.
Haave not checked the output of the fuel pump as of yet.
Boat is a 1990 16' nitro.

 

[JohnnieVee]

Rechecked the above items, did notice that when the engine is running under load, it appears to be running on all cylinders, if I have the engine in neutral and run it up to 1500 rpm, it will buck and spit a couple of times, like the timing is too far advanced. don't have a timing light yet will try to get one in a couple days. Have a in-line spark tester, will see about using it to check the spark on all cylinders, to see if I have a cylinder dropping out.

 

[okbyme]

Rechecked the above items, did notice that when the engine is running under load, it appears to be running on all cylinders, if I have the engine in neutral and run it up to 1500 rpm, it will buck and spit a couple of times, like the timing is too far advanced. don't have a timing light yet will try to get one in a couple days. Have a in-line spark tester, will see about using it to check the spark on all cylinders, to see if I have a cylinder dropping out.

If you don't have a heat limiter on the engine then you have a vacuum leak.

 

[JohnnieVee]

Would the oil tank sensor box also play a part in it? Being a small engine mechanic, I know you have to block off the carbs and exhaust. Where on the exhaust would I block off without separating the engine? or should I try the WD40 trick while running the engine. the problem with that is getting to the upper and lower crankshaft seals.