MR-1 Engine maxing out at 8500 RPM

[Hike]

[USERGROUP=9]@HELP[/USERGROUP]
2008 Sx230HO
First day back on the water this season. After 20 min of boating the port engine started slipping down to 8000 rpm at WOT , starboard engine stays at 10k rpm.
What would cause this slip? Port engine starts to go up to 9k rpm then quickly slips back to 8,000x
There are no warning lights. jet pump clean out port is clear. pee holes are all active.

Newly received from yamaha with new impellers, pump rebuilds and spark plugs. Any ideas?
Frustrated,
-Hike

 

[Scottintexas]

Is the throttle handle moving back?

If so look in our faq section for slipping throttle, it's an easy fix,

Also look at the link in my signature below for common issues/fixes with your model boat



.

 

[Scottintexas]

If it's not the throttle handle then i would guess spark plugs (even if new they the mr1 is finicky) or fuel since its first trip of the season, I'd run it for a few hours or at least a tank and see if it continued

 

[Hike]

Holding throttles in the up position and is still slipping.
I’ll look up the throttle slip faq...
thanks

 

[canadianbob]

having the same problem on port engine - replaced plugs - checked coils & compression - all good. its a job but may change ecu side to side to see if i have a bad one - dont know whats left. (when you throttle up engine will go to about 8600 then immediately drops to 8000 ) may check injectors 1st

 

[Babin Farms]

Check out my fix.

https://jetboaters.net/threads/the-official-what-did-you-do-to-your-jet-boat-today-thread.2661/post-488092

 

[zipper]

How new are the spark plugs? Are all the boots secure? If it was fuel, I think it would happen to both engines. If you are holding the throttles, they are not dropping.

 

[Babin Farms]

@Hike So if you hold the port throttle at WOT it will still lose rpm’s?

@canadianbob sounds like you have throttle drop

 

[Hike]

Brand new spark plugs. I tried the throttle drop mod with the hose clamp. No difference.

 

[Hike]

I pulled her out of the water. Running the port engine on a hose, I’m able to sustain 10k RPM with no drop. Only changes from last season is the pump rebuild, lube steering and throttle cables and spark plugs... Any ideas?

 

[tdonoughue]

Is the oil over-filled? Check the air filters. Maybe you are getting splash as you run longer, which is choking out the engine (and then it sits for a while and improves)?

 

[Hike]

Ahh, interesting. I did top off the oil on the high side before launching. Especially in the port engine. Will check it in the am. Fingers crossed that’s the problem. I dread going back to Yamaha as it took them 7 months to get the pump build done due to lack of parts.

 

[Hike]

Pumped out excess oil. Running at the correct oil level ( at Full when engine is hot).
port engine is still topping out at 8500 rpm. It will hit 9k occasionally then drop right back down. Starboard is hitting 10k.
At idle the port engine is idling one notch below the starboard engine. Wondering if it could be spark plugs.

 

[zipper]

Sounds like you have one bad plug or disconnected spark plug boot.

 

[Hike]

Wouldn’t a bad plug cause a misfire? Engines are running smooth

 

[zipper]

My MR-1 HO's run at 10,200 rpm's at WOT. If you disconnect 1 spark plug, rpm's will drop to 8k-8.5k rpm's on that engine. I have tried it just to see. You may have a loose boot, if you see 9k rpm's then drops.

 

[mrcleanr6]

i had this issue as well on my wifes old ski. i lost 1 cyl. that ended up being a bad injector. the mr1 is super easy to chk injectors. pull the intake off, unbolt the throttle body assy. leave the fuel line hooked up. you can rotate the the throttle bodies around so the injectors are facing up. with it in that position crank the engine and you will see each injector fire. if one is firing different than the others or not at all then you found your culprit.

 

[Scottintexas]

The MR1's are very finicky about spark plugs, I'd check the boots and if that didn't help I'd change all four,
I had an engine start acting funny with RPMs and then would top out at 7500 but sounded fine, changed the plugs and it was back to 10200,


.

 

[Hike]

Checked all the boots and connections seemed fine. No change. Dropped it back off at the dealership :-/

 

[tdonoughue]

Aw, rats. I was going to suggest inspecting/changing the air filter on the affected engine (or swapping it). When an oil overfill occurs, oil can get splashed up on the air filter and cause issues. So just draining the excess oil doesn't always fix it--sometimes you need to change the air filter, too.

Well, we will see what the dealer says.