Help Diagnosing engine issue

[the MfM]

Definitely a clean boat! You did slightly better on price then I did when I bought mine. But mine came with a blown motor lol.

I’ve been trying to buy another one for spare parts that’s been left outside under a tree with a rotted steel trailer. Upholstery is ripped and one engine “just needs a starter”

I offered him 1500 and thought I was being generous. Guy says he has standing offers of 3k but wants more.

 

[cubaniche]

Definitely a clean boat! You did slightly better on price then I did when I bought mine. But mine came with a blown motor lol.

Honestly, all the mechanical work was easier on me than the visual cleanup lol!

The gelcoat was badly oxidized. Like, run your finger down it and come up with a little white reside. It took a full day of straight compound correction little area by little area to get it to shine again. Then polish. Then wax. That was killer on my shoulders and arms.

 

[cubaniche]

I’ve been trying to buy another one for spare parts that’s been left outside under a tree with a rotted steel trailer. Upholstery is ripped and one engine “just needs a starter”

I offered him 1500 and thought I was being generous. Guy says he has standing offers of 3k but wants more.

Holy cow! Yeah he's in for a long wait. I doubt anyone would buy it at that price.

Mine has, what seems to be, the standard tear down the center of the vinyl on the rear seat backside hump. I sewed it and then covered it up with another piece of vinyl as best I could. Other wise, just lightly stained and faded vinyl all around. I'll probably have them redone at some point.

 

[4x15mph]

$1500.... that's a steal even if both engines don't run since you can rebuild them for less than $1K. I bought mine for $8500 in ~2015 and added a lot... then sold it for $8000 5 years later.

 

[cubaniche]

$1500.... that's a steal even if both engines don't run since you can rebuild them for less than $1K. I bought mine for $8500 in ~2015 and added a lot... then sold it for $8000 5 years later.

Yeah this one was listed for a while. I'm in TX and drove to FL to pick it up.

So, upon further digging when taking the pump apart, it spins freely. Nothing is binding or even touching. I guess the sound difference I heard was just "normal". I can spin the shaft from inside the boat with the engine pushed back and there's no wobble or anything that looks like it would cause a problem (other than the rubber isolator in the bearing housing that was loose, but I siliconed it back in and doesnt move at all). Just the sound of the shaft/impeller spinning. The housing doesn't look scratched, the impeller has sharp blade ends, no nicks or corrosion or signs of wear. The only problem is I can't pull it out. I can't separate it from the boat/transom.

So I think I'm not going to cut the shaft etc, and send the parts back when they arrive. I just don't feel like this is a problem. The engine runs, it just won't go past 4k. It doesn't shut off, it runs cool/warm while under way. We ran the boat Sunday for hours. It doesn't shut off or die or anything. So, Im hoping its the temp sensor.

 

[cubaniche]

Well, no go with the new temp sensor. I tried a swap from the port engine too just in case. Nada. Still limits to 4k. Is there any way the CDI itself is bad? Feels like a stretch to me. Last ditch effort is to replace the other two coil packs. I read in another thread that old cables could technically cause the engine not to operate optimally.
I don't think there is anything in the stator that governs RPM? I wish I understood more on how the engine limits itself to 4k during an over heat condition or other self protection trigger. Its a two stroke, not a whole lot of electronics. The only way I can see it doing this is via limiting spark.
Is there a way to bypass the temp sensor that anyone knows off? I traced the wires. One ground one pink. The pink gets split into two: one goes to the back of the CDI with a bunch of other wires (which I assume that behind the rubber is some sort of control board) the other pink wire goes to the wiring harness back to the front. Don't know where it terminates or why it is split and taken to the front of the boat like that.

 

[4x15mph]

Well, no go with the new temp sensor. I tried a swap from the port engine too just in case. Nada. Still limits to 4k. Is there any way the CDI itself is bad? Feels like a stretch to me. Last ditch effort is to replace the other two coil packs. I read in another thread that old cables could technically cause the engine not to operate optimally.
I don't think there is anything in the stator that governs RPM? I wish I understood more on how the engine limits itself to 4k during an over heat condition or other self protection trigger. Its a two stroke, not a whole lot of electronics. The only way I can see it doing this is via limiting spark.
Is there a way to bypass the temp sensor that anyone knows off? I traced the wires. One ground one pink. The pink gets split into two: one goes to the back of the CDI with a bunch of other wires (which I assume that behind the rubber is some sort of control board) the other pink wire goes to the wiring harness back to the front. Don't know where it terminates or why it is split and taken to the front of the boat like that.

Beyond me and I would call jetskisolutions or someone similar to discuss the ECU, wires, and overall issue. Sorry I can't be more help

 

[cubaniche]

Beyond me and I would call jetskisolutions or someone similar to discuss the ECU, wires, and overall issue. Sorry I can't be more help

No worries. Thanks for the reply!

 

[the MfM]

IDK if the Thermo switch is NO or NC. I’d guess it’s normally open so disconnecting it might make a difference.

Have you set the carbs pop off pressure yet?

How about the the flywheel...did you swap that over to the new engine? Might have sheared the key. IF the flywheel slipped I’m not sure it would explain your problems but might be worth checking.

 

[cubaniche]

IDK if the Thermo switch is NO or NC. I’d guess it’s normally open so disconnecting it might make a difference.

Have you set the carbs pop off pressure yet?

How about the the flywheel...did you swap that over to the new engine? Might have sheared the key. IF the flywheel slipped I’m not sure it would explain your problems but might be worth checking.

Thanks! I read a bad or failing stator could also cause issues so im replacing it with one from JetSkiSolutions. Replacing the coils and wires too.

As for the carbs, yes, its fixed now with the right spring. No more dribble and idled much better. Stock needle and seat, plus the 115gm spring has it right around 55psi.

The CDI is responsible for, apart from other things, spark advance/timing, so if its getting a bad signal from the stator, it could be limiting rpm via spark because it thinks something is wrong. I'm treating this now as an electrical issue. Something is triggering the CDI to go into limp mode. Just ned to figure out what that is.

If it was really mechanical, I'd have all the other problems others have had with these engines shutting down, not idling, not starting, turning off while under way, etc. It does not do this. Itll happily sit at 3500k as reported by the stock tach, all day on the water. With never an issue other than the rpm limiting.

 

[dabomb6608]

Just spit balling here. Have you confirmed throttle shafts are opening fully? Chokes not partially closed? If this was a seadoo boat I would be pointing at the shifter switch or MPEM for sure. They have a limiter when not in forward. But these don't. Try and do a OHM test on your stator and coils. Manual has the specs you are trying to hit during testing. I've not experienced this on a yamaha yet that wasn't solved by overheat issue, pump issue, or carb issue.

 

[cubaniche]

Just spit balling here. Have you confirmed throttle shafts are opening fully? Chokes not partially closed? If this was a seadoo boat I would be pointing at the shifter switch or MPEM for sure. They have a limiter when not in forward. But these don't. Try and do a OHM test on your stator and coils. Manual has the specs you are trying to hit during testing. I've not experienced this on a yamaha yet that wasn't solved by overheat issue, pump issue, or carb issue.

Thanks, I'll test it. Need to look up the specs for testing. The stator idea came from a bunch of GP1200 owner threads I read, that pointed at the stator and after replacement, the ski no longer limited rpm. There is nothing wrong with pump. Ive now checked it twice, everything spins with zero contact anywhere and no wobble and no real drag as if something was binding or bearings were shot.

Carbs are rebuilt and run fine now as well. New temp sensor. Its why I'm looking at this from an electronic aspect now. The limiting is just too accurate to be mechanical. It doesn't waver. Gets to 3700-4k and stops.

 

[cubaniche]

There is definite wear, but no contact. I greased the cone but it didn't really need it. Spun just fine, no issues I could tell.




Here's a vid from this weekend. It'll do this all day and not complain, or turn off, sputter, die, not start, etc. Fires right up and runs fine up to that 4k limit.

20200510_164706.mp4

drive.google.com

 

[dabomb6608]

Thats right at the "powerband" on these engines too. Definitely weird. I've had Seadoos with failing coils act very funny as well at certain rpms. And I've had failing CDIs act funny as well. But haven't had the exact situation you are experiencing. Worst case you can swap electronics (whole stator cover assembly and EBox) from one engine to the other to see if it follows the electronics.

 

[cubaniche]

Cool thanks for the info. I figure all this stuff is either original or super old. At least, from what I can tell. So, I don't mind throwing parts at it if it means they are now new and not going to be a source of frustration in the future or a source of doubt. Stator was only 97 bucks. The CDI should ve easy enough to swap and test.

I appreciate the suggestions.

 

[dabomb6608]

Cool thanks for the info. I figure all this stuff is either original or super old. At least, from what I can tell. So, I don't mind throwing parts at it if it means they are now new and not going to be a source of frustration in the future or a source of doubt. Stator was only 97 bucks. The CDI should ve easy enough to swap and test.

I appreciate the suggestions.

Watch those aftermarket stators. Never had good luck with them. Generally I find good used OEM ones before I go the aftermarket route. Last resort is new OEM but thats $$$.

 

[4x15mph]

Thanks! I read a bad or failing stator could also cause issues so im replacing it with one from JetSkiSolutions. Replacing the coils and wires too.

As for the carbs, yes, its fixed now with the right spring. No more dribble and idled much better. Stock needle and seat, plus the 115gm spring has it right around 55psi.

I think you are going to fix the problem with wires/coils and the fix on the carbs. The only other thought is the exhaust assembly and the "3 holes" that get clogged but I think you said you cleaned all of that out. Keep the updates coming....

 

[cubaniche]

I think you are going to fix the problem with wires/coils and the fix on the carbs. The only other thought is the exhaust assembly and the "3 holes" that get clogged but I think you said you cleaned all of that out. Keep the updates coming....

I sure hope so! And yes, I took apart the exhaust on both engines and totally cleaned them out, sanded down all calcium buildup, and replaced all the gaskets including both internal rubber rings.

I'll be sure to keep the thread updated! Thanks again to everyone for their comments and suggestions.

 

[the MfM]

Hopefully that’s it.

I assume you’ve checked the plugs and have good color, right gap etc. Are they NGK BR8HS?

I’d still double check the flywheel while you have the cover off. The timing marks should be at about two o’clock when the #1 cylinder is TDC.

 

[cubaniche]

Hopefully that’s it.

I assume you’ve checked the plugs and have good color, right gap etc. Are they NGK BR8HS?

I’d still double check the flywheel while you have the cover off. The timing marks should be at about two o’clock when the #1 cylinder is TDC.

Yep brand new BR8HS gapped at .025.

I wonder if thats an issue, the timing/setting of the flywheel. Is there a walk through on how to check this or link to service manual that shows you how to set it right? It would be new to me, and this engine has been apart in the past. If things didn't go back together exactly as they should have, that could be the issue.