rpm issues on rebuilt 3.0 merc

[trabich]

Hello all. I need some help here. I just rebuilt my mercruiser 3.0 140 hp motor out of my 84 VIP boat. I had about 2 hours of runtime on the rebuilt motor and everything was doing great. When heading back to the other side of the lake from my fishing spot my rpm's started bouncing up and down drastically. Going from 4000 to about 1000 constintly on WOT. I would then bring the boat back to an idle (which it still idles great) and then hit the throttle again. It would run good for about 5 seconds and then starts bouncing back and forth again. Does anyone have any ideas. The carb was just rebuilt as well.

 

[wire2]

Re: rpm issues on rebuilt 3.0 merc

Sounds like the throttle cable is not secured at the mount behind the carb, and is sliding.

 

[trabich]

Re: rpm issues on rebuilt 3.0 merc

I will check on that. Thank you. I am hoping its not the fuel pump. But I am thinking because its a mechanical pump it would fluctuate like that. A mechanical pump would just go completely out wouldn't it? Plus the replacement pump is 280$

 

[doman]

Re: rpm issues on rebuilt 3.0 merc

sounds like it is starving for fuel ....when you bring it back to idle it gives it time to fill the bowl again ..so i would look at the fuel delivery before anything , filters, float ect

hope this helps

 

[fat fanny]

Re: rpm issues on rebuilt 3.0 merc

Could be building pressure up in the tank and it's not being released via the vent. check the vent.

 

[Adirondack]

Re: rpm issues on rebuilt 3.0 merc

Lets just start with the simple like changing your fuel filter, clean out the water separator if you have one, then check for any other fuel supply restrictions like a kinked hose, or bad anti-siphon valve.

 

[Alpheus]

Re: rpm issues on rebuilt 3.0 merc

Check fuel filters,check fuel pressure. Why are you taking a new engine up to 4K RPM's???

http://forums.iboats.com/showthread.php?t=283269