98 gsxl 951 cant figure it out

[cenzo4dub]

ok so i bought this ski earlier this year with a blown engine (hole in block and piston in pieces). soo i pulled the engine and found a rebuilt one on craigslist (700$)thats never been fired up yet. prob not the greatest idea. so while the engine was out i cleaned the hull changed out all the gray tempo fuel lines cleaned not rebuild the carbs cleaned fuel selector valve new battery 2 new ground wires changed jet pump oil. prob some other stuff also. but anyway here comes my problem. i got the ski fired up runs great but in smooth flat water im only running tops about 4100 rpms and 20 something miles per hour. now if its real choppy out or a big enough boat comes by then it will jump out of the water and hit upwards of 6800 rpms and i can hold top speed as long as i want. as soon as i let off the throttle and try to go again it does the same thing. NOW since then i put a new OEM wear ring, solas concorde 15/20 and neoprene seal also resealed ride plate and pump shoe. also fully rebuilt carbs with new needle and seats, checked pop off pressure (popping around 20 psi on average), ski came with cabron seal set up and i bought another parts ski mainly for body parts i got it real cheap but it had the carrier bearing set up so i swapped that in, and i even swapped mpems. with all this done im still getting the same problems. compression on engine with my cheap guage is around 120 each cylinder which i know you will prob say is low for this engine. but my concern is why it will run top speed if i hit choppy water. what the hell is going on please help

 

[Coastiejoe]

At 120 you are need of a new engine. Lucky it even starts to be honest.

You are hitting higher speeds in chop as the impeller has less load on it and gets the chance to rev up. It would be like running it on the trailer out of the water. No load it will rev right up.

 

[Sportster-2001-951C-Stock]

Might have the wrong base gasket under the cylinders, too thick increases squish too much.

Also, the fact that once the revs come up(when the pump unhooks momentarily) and then it catches and goes like hell sounds like the RAVES aren't opening, or maybe it's bogging lean or missing on one cylinder.

 

[SabrToothSqrl]

120 sounds like the compression gauge is just reading low. Mine reads 120 across 4 engines. All run 6800-7k WOT under load. All 951s.

The carbon ring is the better setup, I'd swap that back, but I don't think it's causing the performance issue.

Your parts ski, what year was it..? The 98 and 99 GSX LTD have several changes, including engine related.

Something feels like this is fuel related to me... That prop will top out at 6800-6900 if the engine is in good shape.

What do the plugs look like? Feels like if the engine can pull enough, it gets the fuel, if not, it's stuck sucking too little.

Check for exhaust leaks as well, that will kill the power.

 

[djredman99]

I am going to agree with Coastie on this one. The fact that everything is fine once you get the load off the prop enough to get the RPMS up suggests your low compression readings are accurate. While under constant load, your engine does not have enough power now to to push your RPMS up.

I don't think it is fuel related, since having fuel problems typically doesn't result in a steadily running (but underpowered) engine.

 

[cenzo4dub]

i should have added that i am getting water in hull when moving not just floating. the plugs are a nice tan color and raves typically operate around 5k rpms but i will double check them. i really dont think its fuel related as i know the carbs are fully rebuilt in working order and ive tried playing with the choke as im riding and only getting it to bog down when i do that which is what it should do and ive tried on and reserve on the fuel selector and theres no differnece at all. and unfortunately the parts ski was from a 97.5 gsxl (which is also a 98 but with white motor) and i didnt know it at the time the only thing in my ski from the 97.5 is mpem and engine. i also changed the pipe to manifold gasket with new bolts and diaper gasket, but i havent split the pipe and checked that one

 

[Sportster-2001-951C-Stock]

Well, 120 in both holes sounds suspicious to me since it was recently assembled and there could be several reasons such as a problem with the gauge even, the wrong base gasket would do this as well. At least they're the same and 120 is usually enough to fire a cylinder reliably but we really need more detail b/c the compression gauge reading could be miscalibrated to the high side and it's really only blowing 90psi and running one just one cylinder, or the battery was barely cranking it over and the reading would be lower than normal in that case.

So for me, there isn't enough info to condemn this engine.

 

[cenzo4dub]

well i will start up and run the engine for a few mins on the hose tmrw and use my coworkers snap on compression tester and compare it to mine after i know the battery is charged up good and theres some oil on the cylinder walls bc everytime i ever checked it it was cold. and i dont start it often bc it isnt running properly so the when i check the cold compression the battery wasnt fully charged up

 

[djredman99]

i should have added that i am getting water in hull when moving not just floating. the plugs are a nice tan color

Are you saying you are only getting water in while moving or both when moving and sitting? Also, how much water are we talking here?

Nice tan color plugs sound perfect. An accurate compression read on that engine in like new condition should be right at 135. That is the same engine I have, white 97.5 gsxl 951.

 

[Sportster-2001-951C-Stock]

Let me add the waterbox valve to my list of gripes, the cone pipe could be flooded with water and not clearing out like it should, as well.

 

[Coastiejoe]

i should have added that i am getting water in hull when moving not just floating. the plugs are a nice tan color and raves typically operate around 5k rpms but i will double check them. i really dont think its fuel related as i know the carbs are fully rebuilt in working order and ive tried playing with the choke as im riding and only getting it to bog down when i do that which is what it should do and ive tried on and reserve on the fuel selector and theres no differnece at all. and unfortunately the parts ski was from a 97.5 gsxl (which is also a 98 but with white motor) and i didnt know it at the time the only thing in my ski from the 97.5 is mpem and engine. i also changed the pipe to manifold gasket with new bolts and diaper gasket, but i havent split the pipe and checked that one

Water getting into the hull is SOUNDING like it is the Carbon Ring.I read your made the swap, but it is basically the same symptom. But even if so, you would get higher RPMs and lower performance. Basically this would let the impeller suck air from the hull which lets the impeller spin with less resistance.

Could be bailers as well, just making a point that even if the Carbon Seal is bad, you still have an issue.

 

[Coastiejoe]

Running on the hose is ok for SHORT times. A couple of minutes is too much time. The Carbon seal and or traditional (older style) do not like it. They get hot fast.