2001 GP800R not going over 3000 RPM in the water

[FoulFowl]

I have a 2001 GP800R that I recently finished a rebuild on and I’m now facing a issue regarding RPM’s in the water.

Carbs are rebuilt and engine was completely taken apart and rebuilt from the ground up with new gaskets, plugs, throttle cable, etc.

Everything seems fine on the ski when I’m testing it with the garden hose attached and am getting 8,000 RPM when I’m at full throttle out of the water. However, when I drop the ski in the water the ski refuses to go above 3,000 RPM no matter what I do. There are no idle or cranking issues with it as well and fires up instantly every time.

Anyone got any ideas on where to start looking to fix this issue?

Side Note:
The person I bought it from had some shop jerry rig the fuel cock system as well for whatever reason and has wires spliced together in order to bypass the fuel sensor.
When I reconnect the wires properly the fuel sensor cause a warning light to flash on the dash.
My best guess is it has something to do with this whacked out fix but, I wanted to get a second opinion before I started throwing more parts at it.

 

[FoulFowl]

Impeller was already checked as well with no issues discovered there as well.

 

[CHRISRACERX]

The fuel sensor won’t make it go into any limp mode. The only thing that does that with that ski is the temp sensor. Did you do all the work? I would maybe take off the fuel selector and make sure it’s clear. If not replace it. I’ve replaced them with the wsm ones and they are fine. You might have trouble removing the screws so you might need more than the selector. Those carbs have to be perfect when cleaning. People try to clean with out removing the fuel screws bc they are seized. It never really works. Also try rebuilding them with non Mikuni type carb rebuild kits. I can never get those style carbs to seal with non Mikuni kits. Also make sure the powervalves are moving effortlessly when turning by hand. You have to remove the bracket and cables off the drum for this. If they don’t they need cleaning. There is a proper way of installing the cables also for tightness and movability. Also check the gas. If there’s water and junk and the gas and it wasn’t removed. Just Cleaning the carbs is a waste of time. For start up will have dirty carbs again. Also a lot of people when cleaning the carbs don’t check the accelerator pump. Idk why. It’s part of the fuel system

 

[FoulFowl]

Yep I did all the work on the ski and the temp sensor was the very next piece I was planning on swapping later tonight. I actually have the replacement from another ski in my hand that I was planning on swapping in today as that was my initial thought.
I’ll make sure to double check the accelerator pump but I know for a fact that the carbs aren’t seized as they came off a running freshwater GP800r and I rebuilt them with a fresh kit.
I’ll check the temp sensor and the accelerator pump but, I’ll keep in mind the potential issues with mikuni carb kits when I’m rebuilding skis in the further. I’ll post an update in about 5ish hours when I get a chance to work on it again. Fingers crossed it’s just a foul sensor.

 

[Jcary85]

Here’s what I’d check in order:
1. Spark to both plugs
2. Good Compression in both cylinders
3. Disconnect temp sensor and see if it’s fixed
4. Fuel line routing
5. Take carbs apart and check everything
6. Ohm check the pickups
7. Ohm coils
8. Swap CDI and test

Motors running on one cylinder with a hole in one piston can rev to 8k on the trailer so this isn’t that surprising.

 

[FoulFowl]

Alright I’ve just now gotten a chance to get it back on the water and run some tests and the following has now happened...
After replacing the temp sensor with a new one the ski still won’t accelerate over 3000 rpm. I’ve replaced regulator/rectifier on the ski as well thinking it may have been a loss of power in the ski at higher rpm...

After messing with it about another hour on shore and swapping everything around with known working parts from my gp760 the ski still refused to go over the 3000 rpm...

After I got home I checked the compression on both cylinders and am getting 120/120.
I ran the ski out of the water to flush it out at home and tried going above 3000rpm and got 8000+ rpm out of the water no issues...
However, I noticed that the power valves on the ski weren’t turning over till about 6000+ rpm was indicated.
This seems kind of strange to me and seems like my power valves are potentially at fault for the ski not going above 3000rpm in the water. I read in the owners manual that you can tweak the slack in the cable moving the power valves.

So my question now is if I tweak the cable controlling the power valves could I potentially get them to rotate sooner as 6000 rpm seems to be way to high for them to start turning over. If I’m taking a guess on it seems the power valves are causing a loss of power in the ski as they don’t open up to allow higher than 3000rpm in the water

 

[WB800BLASTER]

check the PV motor they go bad all the time. Un plug and take off the cables. hold the valves open manually and test it on the trailer.

 

[FoulFowl]

I’m having no issues with rpm over 3000 on the trailer or with the hose attached it only starts limiting rpm in the water the pv motor seems to be working however as the pv motor has a send retract check after the engine is shut off for 3 seconds and the motor properly is working on that check so I’m thinking the motor is good.

 

[FoulFowl]

Alright got a chance to disconnect the pv motor last night. When I turn the pv by hand the engine sounds a whole lot better the pv also is loose and turns by hand with ease...

I’ll be dropping it in the water sometime later in the upcoming days will keep this updated on the condition in the off chance someone else has the same issues on their ski.

The only other question I got now is that if manually turning the pv fixes the issue would the next step be buying a new YPVS cable or a replacement servo motor assembly all together? Or would I be fine with just manually turning the power valves and keeping it locked in the open position?

 

[WB800BLASTER]

If the cables move freely then they are fine.........when PV motors go bad they still cycle but don't work right when running under load.

The PV's should move with ease and if they don't clean them. As you have it apart it would be good to clean them as the will be full of oil / exhaust crap.

 

[FoulFowl]

Alright after dropping it in the water and manually holding the power valves full 1 way full the other way and even holding it in the center yielded the same result as before I’m at a loss with this ski for now about to just give up on her and take it to a local repair shop to try to see if they can have any better luck than I do...

Power valves seem to not be the issue and I’m completely lost on what to do next if anyone has got any pointers at all before I take it to the shop please let me know...

Engine is acting fine out of the water 8000+ rpm no problem but the second it’s fully in the water it’ll drop to 3500 rpm...
Compression is 120/120 and revs and everything out of the water.
Carbs are rebuilt and gaskets are brand new on it, everything was cleaned of any visual buildup to make sure it’s a factory seal and I’ve replaced a dropped power valve on it as well.

Edit: As I was reconnecting the power valve cable I noticed this... Is it supposed to have 2 or 3 cables going into this connection cause it appears the third one (if there is one) is cut off

 

[Jcary85]

Can you maybe post a short video of it running and revving up out of the water? I’m curious if it sounds healthy.

 

[FoulFowl]

Can you maybe post a short video of it running and revving up out of the water? I’m curious if it sounds healthy.

Short video of it revving with no issues (this is with the power valves disconnected)
https://youtu.be/1hNN8ckNA_4

 

[Jcary85]

I could be wrong but that sounds like it takes forever to rev up. Does not sound right to me. Sending to a buddy with an XL800 to compare. I’ll let u know what he says

 

[te4250]

Sounds like a lean bog there at 6.5 seconds

 

[Jcary85]

Have u checked the power valves aren’t broken? Apparently u can see them in the spark plug holes - that’s a suggestion from local guy with an XL800 who just blew it up when valves broke/dropped.

 

[FoulFowl]

Yeah I had to take apart the whole ski when I bought it and noticed it was missing a power valve b4 I had owned it the previous owner also deleted the fuel cock for whatever reason as well and has some nifty wiring up front to turn off fuel sensor warnings etc

 

[CHRISRACERX]

Pretty sure the wire cut is the signal wire. Gonna need that. N the motor doesn’t sound correct in that video. Make sure the valves are good n moving. Stop running it if they are not. It won’t fix itself. Does the p/v motor go thru it’s cleaning cycle after the ski is shut off? Basically opens and closes. If the valves are stuck or sticky from residue or tight cables it will burn out the motor. Everything has to right with the Yamaha PV engines. The 1200s are worse bc there’s more stuff to take off when fixing it

 

[FoulFowl]

Yeah I haven’t ran it in the past week now just in the process of waiting for parts and pulling known working parts off the 800 to troubleshoot the 760 both will be up and running once the parts come in just adding to the list for now

 

[FoulFowl]

I know this is an extremely late update but, managed to get it working about a month ago, been holding off on this one and have been working on the GP760, 1200R, 717 GTI and 800XL.

Turns out one of the power valves was broken and wasn’t actually actuating. Luckily I had wave eater clips but, when I removed the PV covers I noticed the left cylinders PV had significantly more buildup compared to the right cylinder. (Right cylinder had the broken PV)

I ended up having to take out a bit with a dremel from the PV slot as the replacement PV didn’t actually fit the old slot. (I’m assuming this is due to the ski running with a busted PV for a good bit)

Had to fully remove the lever link and cylinder in order to get the busted PV out but, fully rebuilt the engine while I was at it as there were dings in both pistons and cylinder head.

If anyone else has this issue with freshly rebuilt carbs it’s likely a Power Valve related issue.