kerrybuch17

Used my boat 2.5 weeks ago for a poker run and ran great. I was getting about 5100 rpm or so at WOT on both motors. I decided to do some maintenance work on the motors and changed the oil and spark plugs on both motors. Take the boat out last Thursday to test and all of a sudden I can't get over 4000 rpm at WOT on both motors. Pulled boat out the water and put on hose to flush out motors and while flushing each individually I revved the motors and each got over 5000 rpm. All plug wires seems to be on correctly and tight. What could be the possible issue why they all of a sudden won't turn over 4000 rpm with a load on them?

Wildman_grafix

A rule of thumb, if something is working then you mess with it and it doesn't work.

Re check everything you just did.
Plugs gaped right, maybe a bad one. Put the wires on wrong. Etc.

kerrybuch17

I'm pretty sure all wires are correct because they are set at a length that only reaches each spark plug specifically. I'm thinking it might be a gapping issue also but why would it allow it to rev over 5000 out the water and only be able to get to 4000 in the water with a load?

SB

It takes relatively no air and no fuel and no spark energy to rev a motor to redline in neutral. Say, 15 hp or so.

DINOKOS

HELLO GUYS, I am new too the forum, i have the same problem with my 1999 sonic 260 prowler, i can't get over 4000 rpm, running great all season, but i didn't go wot all the time, got 4800 in the begining of the season and did 69 mph on a 4blade 23 revo prop. i changed the filter ,checked the anti siphon ck vlv,( which it doesn't have now from previous owner)when i go 1/2 way with throttle to 4000rpm but when i push the throttle up it just stays at 4000rpm, slight surging,and running a little rough today, seems to be getting worse. when i back off it seems to recover and smoother, no pops or backfires. pulled the plugs and they look great, BUT THE CAP AND ROTOR WERE HEAVILY CORRODED, i HOPE THAT IS MY PROBLEM! I put a vacuum to the regulator and it holds a vacuum.i took it out and beat on the boat hoping to clear it out. after i shut it down and restarted it got it up to 4400 rpm but came back down to 4000 after about 1 mile. i will put on fuel pressure gauge soon to help troubleshoot,but is there a safe mode or a rev limiter on these engines, thanks in advance DINOKOS

RaggedEdge

Rev it up to 5K or better out of the water with no load, who's brainstorm was that. You can do all kinds of bad chit with that.

Like said above if all was well before you masterminded it, then go back thru everything you did. Your problem is in there.

DINOKOS

hey guys, i figured it out. I think this will help you all out too. It turned out to be my vacuume line to fuel pressure regulator. The vacuume line collapsed above idle trapping the vacuume in the line which maked the fuel pressure regulator think its in a low power mode never letting the fuel pressure regulator open up to give full psi in w.o.t. I put a new line and tested the boat yesterday and is running great now. The original vacuume line felt spongy and soft, i was lucky to notice it when i was putting a vacuume to the line it was collapsing close to the vacuume port on the engine. A quick test is to turn key to on with fuel pressure gauge, should jump up to 45psi then the relay kicks off the fuel pump it will hang at about 35 psi. Run the engine at idle it should be at least 30 psi, then just pull the vacuume line from the vacuume eng port and if your regulator and fuel pump are good it should go upto 45psi. I couldn't believe this kept the boat from going past 4000 rpm, but always look at everything that is related to the system and don't leave anything out (like a simple vacuume line!!!!!!!!!!!!) i hope this helps you all who have the same problem, thanks dinokos