I have a 2yr old Merc 383 MPI reman, and ever since day 1 (well, at least day 1 after break-in) the motor will not spin past 4000-4100 RPM in gear. It sounds as if the rev limiter is kicking in.

The motor WILL spin up to the 5200 limiter in neutral. In gear and at the 4K range, the frequency of the noise is much less frequent.

Could it be a prop issue? I doubt it, just because my old motor would spin the same (same model & pitch) prop over 6K. The motor accelerates just fine up until it hits this wall.

At first I thought it was my pickup tube placement was causing prop ventilation, but I just recently relocated it and I have the same problem.

Thanks in advance,

I would start with checking the fuel pressure on the fuel rail at that speed.

What should the pressure be?

Thanks,

Signed, missing my carburetors...

38 psi with the fuel regulator vacumm hose left on, Then it should jump up to around 43psi when you unhook the vaccum hose with the engine running.

is there a little switch by the throttle that is not being used?

I will have to look. I am assuming by the throttle body?

It held 43 Psi, so it doesn't look to be a fuel delivery issue.

Tried a different prop (next size up) and it still acted like a rev limiter @ 4100.

I wouldn't free rev a engine that high not under load, I have read its hard on the engine

yes by the throttle body were the linkage hooks up when
you put it in gear the arm pushs on the little switch
it is a cut out switch when in and out of gear..