Yamaha FX 140 speed issues!

[pwcridingmachine]

Hi all, I really need some help to figure this one out. Let me start by saying that i bought this ski just about 2 months ago. It had 455.5 hours on it when i bought it so im assuming that it was possibly a rental unit. The engine runs very well, starts right up every time with no hesitation at all. The first time i had it out it ran great but i noticed cavitation and top speed was only 40mph at W.O.T. When i got it home i noticed the oil filter was soaked in oil, so i bought an R&D filter to replace it, changed the oil and spark plugs. I also checked the impeller and noticed it was ate up with cavitation pits.so i found an entire jet unit for a good price on ebay. It actually had a solas concord impeller already in it. Anyway got it installed, hit the lake and it was definitely better. However it still cavitates slightly and top speed is only 45mph now. I'm getting 10,000rpm at W.O.T , so im stumped on what the problem is. I know that top speed on this ski is around 55-60 with one rider and im 175lbs. Also i haven't checked the waer ring/impeller clearance but it looks to be right. Anyone had this problem before? Please help! Any help is greatly appreciated!

[grumpy_steven]

Are you sure you're hitting 10K RPM? With one bad spark plug, the ski will seem OK, but top out in the low 40's. These motors will toast a plug without much warning. And even if you replaced the plugs, it doesn't mean they are all good.

[Ski Hacks MG]

When i got it home i noticed the oil filter was soaked in oil, so i bought an R&D filter to replace it, changed the oil and spark plugs.

Do you mean air filter? If so, overfilling with oil is a very common problem and will rob speed once it pukes back up into the air filter.. When you changed the oil, did you fill to the halfway mark between low and high on the dipstick?

[YoYamma]

Anyway got it installed, hit the lake and it was definitely better. However it still cavitates slightly and top speed is only 45mph now. I'm getting 10,000rpm at W.O.T , so im stumped on what the problem is. I know that top speed on this ski is around 55-60 with one rider and im 175lbs. Also i haven't checked the wear ring/impeller clearance but it looks to be right. Anyone had this problem before? Please help! Any help is greatly appreciated!

Probably won't see 60, more like 53-55 mph.
Remove the air filter, take it out and run it and see what kind of speed you get. Look into the Riva Velocity Stack kit Jerry sells here in the store.
Air filter needs to go; (notorious for reducing speed on this model) Riva sells a special power filter to go with the Velocity Stacks that will eliminate this oil clogging problem.

As CCW said, overfilling the oil is very common; not good and will scrub speed. Checking oil level should be done when ski is sitting perfectly level at normal operating temp; we check ours in knee deep water after a ride.

Already replaced plugs, could be the wear ring.
Almost 500 hours - that ski has seen some fun times!

[pwcridingmachine]

Thanks for the replies fellas. Yes i meant an R&D air filter is what i replaced the stock air filter with and at the same time i did an oil change , oil filter replacement, and new plug change. With the stock air filter i was only getting 9500 rpm at best so i had already did what you mentioned (removed the stock filter and ran without it) then i was getting 10,000 rpm. I already knew that it needed to be replaced so i went with the R&D air filter over a new stock paper filter. I just sealed the entire pump shoe and filled all cavaties, pulled the jet pump unit done a full inspection and can't find anything significant that could be at fault. While I've got it out and dismantled i gently filed out small knicks and sharpened the leading edge of the impeller blades. Everything now looks great! Ill report back after i get it put back together and hit the lake. Just wondering if the engine can still hit 10,000 rpm if one plug is bad? What are the clearance specs on wear ring/impeller? Could a bad driveshaft seal cause this? I mean if its bad wouldn't it draw air from inside the hull directly into the pump? One other thing that I want to mention is that ive had several jetskis over the years from a 6400cc-1200cc engine. My point is that they've all had that mid range power or thrust! Say I'm going 30mph then just clamp down on the throttle I get that really hard pull or get up and go power that shoots up to top speed really quick! The fx140 I've got now doesn't have that really strong hard thrust/pull like any of the other ski's that I've had! Why is that? The engine power is there, its just like i can't get it to the pump. Hope that makes sense lol. I really appreciate any and all help and input. I want to get this hog running right. Let me know your thoughts please.

[Ernest T]

Top speed on that ski will be around 53 mph, and you can't rely on the speed-o. Check it with a GPS, because the speed-0 can easily be off 5 mph in either direction. If you are hitting 10,000 rpms the engine is good and the problem is in the pump. Look carefully at the blades for dents and nicks. The clearance between the housing and the impeller should be less than 0.5 mm all the way around.

[pwcridingmachine]

I took the ski out yesterday and it was definitely better as far as hole shot take off and about 3 more mph on speedo, but it still cavitates. While it on the trailer in the water i ran it and watched the water coming from the exit nozzle. I noticed at idle just clear water coming from the rear but at around 2000rpm i start to see bubbles in the water coming from the nozzle and gets worse as i increase rpm. Is this cavitation bubbles im seeing? Is it possible that the pump is sucking air from the drive shaft? Possibly a bad drive shaft seal?

[pwcridingmachine]

Anyone? Any ideas? Are the bubbles normal and my problem is something else?

[kwtony]

impeller housing...needs replacing. Always the number 1 thing on these older fx skis. Youll get yours speed back. buy the full assembly for 310 and not the wear ring for 299...bolt in and go