wont go above 1800rpm under load

[robw22]

I purchased recently purchased an 86' four winns horizon 190 with a mercruiser 5.7 magnum. The block was cracked, so I rebuilt the engine. It runs great in Neutral, and revs up fine, but once I'm in gear, with a load on the engine, it wont go above 1800 rpms. No sputtering, just wont rev. I checked the timing, and it set to 8deg btdc, and all the plugs are firing. It seems to be blowing alot of steam out the exhaust, (thru-hull) and I'm wondering if this sounds like water in the fuel? Any suggestions would be greatly appreciated. Thanks

 

[Maclin]

Re: wont go above 1800rpm under load

Have you checked compression since it was installed? See what that shows. If low, then it could be valve lash settings.

Check the dwell on the ignition, if not in spec that will allow the engine to still start good and run with no load but improper dwell means low spark and will not run well under load. If you have points style ignition then setting the gap is only one step, the dwell has to be checked and the gap adjusted again if dwell is off. Note that if any adjustments are made to the dwell then timing must be adjusted again as well (AFTER dwell is correct).

Also check the mechanical timing advance in the distributor. The rotor should turn just a bit then snap back.

I would also check total advance with a dial back timing light just to be sure the advance curve is in play.

 

[Maclin]

Re: wont go above 1800rpm under load

Usually water in the fuel will cause sputtering and back firing and eventually no start at all.

 

[180shabah]

Re: wont go above 1800rpm under load

There are many many reasons for a boat not to reach proper WOT. FWIW - stop revving the crap out of you engine in neutral, it is diagnosticaly useless and destructive.

There are a couple of great write ups in the adults only section you should read that cover "can't reach WOT" and troubleshooting your fuel system.
Also, in '86 there should not be any points on a mercruiser, so after setting initial timing, that is it.

With rebuilt engine, did you reuse the cap, rotor, plugs, wires, fuel filters etc; or were they all new as well?

 

[diehard]

Re: wont go above 1800rpm under load

check your fuel pump ,fuel filter will cause it not to run at high rpm's did you ever see the boat run before you rebuilt the moter there is a chance some one installed the wrong prop

 

[J. Mark]

Re: wont go above 1800rpm under load

does it make a giant sucking sound through tha carb when it won't go any faster?

Look and see if your timing is advancing as the engine revs up, if not, then your distributor is not advancing properly.

Pull the points plate and check the mechanical weights and slides.

I have also seen one distributor where someone replaced the hold down screws on the plate with new and longer screws, which kept the weights from advancing the timing