951 low max rpm

[Mraw]

Hey all, first full tank after break in reached max RPM of 6950, next day 6880 to 6900, now today 6740 to 6830. Only thing different between rides was that a fogged my ski after every use, perhaps I founded a plug? WRV is great, carbs rebuilt with genuine mikuni, fuel selector bypassed, spark plug wires cut back 1/4 inch, I noticed that the boots have a good amount of a black dust that was also on the plugs, will replace tomorrow. Had this same issue with my previous engine, some days maxing out normal RPM others 300 below. Any thoughts?

Ski is a 1998 gsx limited

 

[SabrToothSqrl]

well, it is 22 years old... if you're above 6500 you're doing just fine. water temp, air temp, weight, fuel level, fuel, etc. all play a role. If you're really picky you can try cleaning the raves to make sure they slide easy, check the rave valve assembly at the water box. if you want the Solas Concord (I think it's a 15/20?) is the best prop for the 951 that I've seen. Ran that on my 951s.

Really, with a carb, no thermostat, 2 stroke, just ride it, 300 RPM isn't worth chasing. Trust me, I have.

 

[Mraw]

well, it is 22 years old... if you're above 6500 you're doing just fine. water temp, air temp, weight, fuel level, fuel, etc. all play a role. If you're really picky you can try cleaning the raves to make sure they slide easy, check the rave valve assembly at the water box. if you want the Solas Concord (I think it's a 15/20?) is the best prop for the 951 that I've seen. Ran that on my 951s.

Really, with a carb, no thermostat, 2 stroke, just ride it, 300 RPM isn't worth chasing. Trust me, I have.

Thanks, I ride a small lake only 25 feet deep and it was 20 degrees warmer yesterday than before. I cleaned the raves when I put the new engine in. With that prop is their an advantage to acceleration and top speed?

 

[Mraw]

So one thing that baffles me is that my first 3 rides where only 1 day apart, air temp went up from 60 to 80. I was on a low tank when I hit 6950 but on a full tank at 6900, today I went out again, new plugs gapped properly and 6830 max. Going to test rectifier tomorrow and maby new battery.

 

[etemplet]

Personally, I wouldn't go throwing money at the ski unless I found an issue. It is easy enough to check the battery and the charging system. Check your spark plug cap connections. Make sure they are tight. Check the resistance on the wires. Replace the spark plugs. Have a look at your Water Control Valve, and rave valves. None of that costs very much. Good Luck.

 

[Boyd12]

After checking the above mentioned items, maybe you should check the plugs (plug chop) when it is running well (6,900) and when it is only pulling 6,740 and see if there is a difference. if there is, it probably will not be much. Good luck!

 

[amcreativ]

I literally just had this happen this weekend. My '98 GTXL 951 runs up around 7050 RPM full throttle and holds steady. Each time I went out my max RPM went lower and lower. It's now around 6500 and only about 84 km/h. When it's at 7050 RPM, I'm usually running 93 km/h, sometimes up to 96 km/h if I'm extremely lucky. I'm going to pull my RAVE valves and clean them, new plugs. and see what happens. Either way, it's ready for winterization soon, so I'm not too concerned at chasing the problem until spring. New motor too, so I am worried a bit. We'll see.

 

[Mraw]

I'll post here if my issue goes away, I was going to test my rectifier and everything mentioned above but it seems my stator has shorted out, going to pull mag cover now and explore, hopefully that was related to my issue

 

[Boyd12]

I literally just had this happen this weekend. My '98 GTXL 951 runs up around 7050 RPM full throttle and holds steady. Each time I went out my max RPM went lower and lower. It's now around 6500 and only about 84 km/h. When it's at 7050 RPM, I'm usually running 93 km/h, sometimes up to 96 km/h if I'm extremely lucky. I'm going to pull my RAVE valves and clean them, new plugs. and see what happens. Either way, it's ready for winterization soon, so I'm not too concerned at chasing the problem until spring. New motor too, so I am worried a bit. We'll see.

If it was mine, I would start looking at it now so when warm weather returns, I am ready to ride!

 

[amcreativ]

If it was mine, I would start looking at it now so when warm weather returns, I am ready to ride!

I did just that. I took a peek at it today and I think it might have been as simple as bad plugs. Put a new set in and no issues. I still intend on pulling the rave valves and cleaning them up nice...again. They seem a bit gunky, but very little carbon. I'm surprised Amsoil Interceptor oil is gunking up this bad.

I also did a compression check as well, things seem okay there as well. I'll probably water test tonight when it isn't so windy.

 

[Boyd12]

That is great news!

 

[Mraw]

So, took off my rave caps and oil everywhere, replaced the bellows with a SBT one I had lying around and went for a rip. Max RPM 6830 to 6880. Thought I had the issue fixed but today 6700 to 6790. Same temps and conditions as last time.

Something else I noticed. At WOT it would sometimes max out at 6660 ish, if I let out the throttle to around half and then went WOT again it would hit in the range of 6700 to 6790.


Also, this ski is fresh on its 3rd engine, origenal rave valves, trimmed down of course. But it has 500 hours total on everything else. Could the stem on the valves be worn out causing my issues?

 

[Mraw]

So today decided to check my fuel filter, surprisingly there was a decent amount of sediment, perhaps somehow one of my gas cans became contaminated. Just for shits and giggles I also moved my WCV cap a little bit past flush. Ski hit a max RPM of 6930. Hopefully my issue will finally be fixed, going to go out multiple times this week.