Not getting the RPM's I should??

[victoryinerie]

I have a 1989 5.7 Merc V8 and it seems to run fine, it occassionly will have a small backfire however I do not believe I am geting the RPM's I should. I can get about 4,200 and that's it. I changed the plugs, wires, rotor, distributor cap, I have tried a couple different props.

Any other suggestions, I have not messed with the carborator, the boat sat for 3 years before I purchased it last year...

Thoughts?? I hate to mess to much because it does seem to run just fine....

 

[aktrucker]

Re: Not getting the RPM's I should??

I have a 1989 5.7 Merc V8 and it seems to run fine, it occassionly will have a small backfire however I do not believe I am geting the RPM's I should. I can get about 4,200 and that's it. I changed the plugs, wires, rotor, distributor cap, I have tried a couple different props.

Any other suggestions, I have not messed with the carborator, the boat sat for 3 years before I purchased it last year...

Thoughts?? I hate to mess to much because it does seem to run just fine....

How much have you used it since you purchased it before problems, or were the problems stated there the entire time and just think it is off? Is it points or elec ign, and if points when were they last replaced? I'm gonna say a carb rebuild is probably in order after sitting that long.......and have you changed the fuel/water seperator?

 

[aktrucker]

Re: Not getting the RPM's I should??

Thoughts?? I hate to mess to much because it does seem to run just fine....

If it "seemed to run just fine" you wouldn't be on here asking what is wrong..... It may run OK, but but I bet you want better than OK..... just sayin

 

[victoryinerie]

Re: Not getting the RPM's I should??

How much have you used it since you purchased it before problems, or were the problems stated there the entire time and just think it is off? Is it points or elec ign, and if points when were they last replaced? I'm gonna say a carb rebuild is probably in order after sitting that long.......and have you changed the fuel/water seperator?

The problem existed since I purchased it thats when I started playing with the prop pitch. I currently have a 4 blade, 16.5 pitch which I think I should be able to get high RPM's out of it. It has and electric ignition, I did change the ignition module inside the distributor. I have also changed the water separator. I also timed it when I changed the wires, plugs, etc...

 

[Brewman61]

Re: Not getting the RPM's I should??

Sounds more like a fuel problem to me than an electrical one. I think the earlier suggestion to rebuild the carbureator may be the ticket. If you're handy it's not terribly hard to do.
Also make sure your fuel line isn't restricted by a partially clogged filter or bad tank venting, etc......

 

[aktrucker]

Re: Not getting the RPM's I should??

Sounds more like a fuel problem to me than an electrical one. I think the earlier suggestion to rebuild the carbureator may be the ticket. If you're handy it's not terribly hard to do.
Also make sure your fuel line isn't restricted by a partially clogged filter or bad tank venting, etc......

Also, if it sat for so long the rubber fuel line may be bad.....I replaced all of my fuel line this year, one of the lines you could see "bubbles" on the inside when looking thru it. I had been picking up small rubber pieces in my filter, that issue is gone for $15 worth of fuel line.....and don't go cheapo with automotive fuel line, buy the coast guard approved stuff...

 

[Bondo]

Re: Not getting the RPM's I should??

it occassionly will have a small backfire however I do not believe I am geting the RPM's I should.

Ayuh,... That indicates a fuel delivery issue,...
After reading more,...
I'd start with a Compression Test...