Can’t get over 3400 rpm

[Mountain fun]

I have a 1994 stingray 536 zpx, when I purchased it the owners did not properly winterize it so I replaced the engine with a local shop reman 4.3 marine engine. I have it all back together and when I take it on the water under a load it won’t go over 3400 rpm. It has the thunderbolt iv ignition and from what I have found does not require to be grounded when timed. It timed at 12 degrees advanced and runs smooth however won’t go past the 3400 rpm. I have checked the exhaust flappers and stripped and cleaned the carb. New cap and rotor, had 1 year old treated fuel and replaced it before cleaning carb and checking filters. I have good fuel pressure. Here’s the tricky part there is a white and thin blue stripped wire that is placed where the thunderbolt V ignition has the grounding wire for time if that is not used for any other purpose. Anyone know if they started doing that with the thunderbolt IV and may need to be grounded when timed? I have read every blog regarding not getting to full rpm and have went through the checklist. It will go to 4600 rpm when free Reving the engine it is just under a load. Thanks in advance engine serial number OD707684

 

[alldodge]

Your serial number 0D707684 shows it has a TB4 ignition and timing would be 8 BTDC

Unable to find a White/Blue but can find a Tan/Blue which may be what your seeing :noidea:

Don't pay any attention to how much the rpm will increase under no load, its meaningless. The only real measure it what it does under load

 

[Mountain fun]

Thank you, it may be tan and blue wire, it is a little off color I just thought it was possibly weathered. I will continue the process of elimination.

 

[alldodge]

You know it could have to high a pitch prop on the drive. Many boaters change the prop thinking if they can get the motor to turn less rpm at cruise they will save fuel. In actual results it increases the amount of fuel being burned and is hard o the motor

What prop is being used, and what ratio drive?

 

[Scott Danforth]

There is the list of things to look at for low WOT in the stickies

 

[Chris51280]

Mine did the same thing. I had plug wires switched on cylinder 1 and 5. Check that all you cylinders get spark and that all the plug wires go to the right distributor point