I have a 1989 mercruser tops out at 3000 rpm

[dmiles452]

I have a 1989 mercruser 350 cu in GM that will not go above 3000 rpm. It gets the boat up on plane but 3000 rpm is all it will do.

 

[alldodge]

Hows the compression?

 

[Scott06]

would also check fuel supply and timing including total advance.

 

[dave8311]

Has this engine/drive/prop combination ever reached the proper rpm?

 

[dmiles452]

Hows the compression?

Engine was rebuilt 3 years ago and only has about 50 hours on it

 

[dmiles452]

Has this engine/drive/prop combination ever reached the proper rpm?

Yes, it has been run at 4500 rpm

 

[flashback]

How did it run 3 years ago?

 

[Scott06]

Engine was rebuilt 3 years ago and only has about 50 hours on it

Should still be ok , but Worth a check to see what it is currently.

 

[flashback]

Tune it up..

 

[dmiles452]

would also check fuel supply and timing including total advance.

Where should total advance be? Fuel supply is good

 

[Scott06]

Where should total advance be? Fuel supply is good

Not sure if you have a thunderbolt ignition or earlier points... If TB the module usually will say V8-22 or V8-24 the 22 or 24 or whatever is on there is the degrees of advance added to intial timing.

As a rule of thumb would think 28-32 total by like 2800-3k rpm should at least be between the ditches.

If you are not advancing due to module or earlier centrifugal advance getting hung up you wont make power

Also might check spark strength with a spark gap tester

 

[flashback]

Is the tach accurate?

 

[Scott Danforth]

Engine was rebuilt 3 years ago and only has about 50 hours on it

What are the compression numbers today?

How old is the fuel?

TB IV or points? If points, when did you service them last

 

[alldodge]

Engine was rebuilt 3 years ago and only has about 50 hours on it

Still might have been running a bit lean and burned a piston or a valve

 

[kenny nunez]

Make sure that the choke linkage secondary “lock out” on the carburetor is allowing the secondary air valve to open. With the flame arrestor removed hold the choke butterfly open and try to push open the air valve.
Which carburetor do you have, Rodchester or Weber/Edelbrock?

 

[dave8311]

What parts were changed or service was done just before the maximum rpm dropped from 4500 to 3000?

 

[dmiles452]

What are the compression numbers today?

How old is the fuel?

TB IV or points? If points, when did you service them last

I dont know about compression numbers, I have not checked that. The fuel is 3 months old and it has TB ignition with module replaced at end of last year.

 

[kenny nunez]

It appears that you have fuel injection. There is a switch on the shift linkage that prevents the engine from high RPM if the drive is not fully engaged. This switch needs to be checked.

 

[dmiles452]

It appears that you have fuel injection. There is a switch on the shift linkage that prevents the engine from high RPM if the drive is not fully engaged. This switch needs to be checked.

No FI, carter 4 barrel carb

 

[kenny nunez]

Is this carburetor the original one that let the engine go to 4500 rpm?