Speedster HELP NEEDED

[yamaha188]

My 99 Speedster has one motor that has been starting to surge. As you run across the lake at speed the rpm will drop and maybe hold for a little then it comes back up. A first it would do this and run like that for a little while then clear up and run fine the rest of the day but now it keeps doing it. On a recent trip out that motor quit and would not restart so i took it home and the next morning it would start but when you tried to give it gas it would die. I pulled the fuel line and it did not have a very good flow so i put a new mikuni high flow fuel pump on (same set up as the other motor) and replaced the lines to the carb and the vacuum line and a new filter. Yesterday i took the boat out and i am still getting the surging. When i run it full throttle it may run up to 7000 rpm and as you go it will drop down in rpm to maybe 3-4000 then run a little and come back up to 7000 rpm. I did notice that if i back off to around 5000 rpm i did not get the surging as bad, this makes me think its a fuel issue but at this point im not sure and dont know what to do next. If anybody has any idea of what it may be please let me know. Thanks

Since this post i have tried numerous things and still get the same results. Tried lots of things and thought if it went from one motor to the other i would know what it was. IM not sure where to go from here but any help is greatly appreciated. Here is the list of stuff i've tried.

1. swapped carbs from motor to motor.
2. new rotary valve and sanded the cover down smooth, clearance on the valve checks good.
3. swapped water regulator from one exhaust to the other.
4. swapped where the fuel line comes out of tank.
5.Ran long pulse line from opposite motor to motor. (Thought maybe not getting a strong vacuum off the motor.)
6. Double checked the timing on the rotary valve.
7. pulled line off at carbs and made sure its getting good flow.
8. bypassed fuel filter. (seen on here where these fuel pumps can collapse the paper filters)
9. checked compression on motor. (145)
10. new fuel lines from tank to carbs and new pulse line.

 

[ialonso]

You have certainly tried many things that could all cause it. In my experience (likely similar to yours, or lower, since you did all these things already) it's either fuel restriction OR Air making it's way to the line. Not sure how to test for it (I have a fuel bulb from an outboard that comes to mind., or use an electric fuel pump if you have one laying around..) try to draw fuel right before the carb, and make sure no bubbles come with the fuel. I remember a faulty ring in a fuel filter (which you have already bypassed) causing the same issue for me. It was not "lack" of fuel, but extra AIR with as much fuel as you wanted, and it resulted in the same thing. (I'm sure to the engine it's the same problem; the expectation that a certain volume of fuel will be fuel only and not a bunch of air)

If you have everything still apart, I would try to swap the line at the carbs from one engine to the other instead of at the fuel pickup.(Major effort, but not more than most you have done already)

the other thought is to examine the lines and fittings to check if anything noticeable could cause air to get in the line (Loose fitting/cracked line or t-fitting or similar)

Good Luck

 

[Coastiejoe]

Do the boats have a fuel selector like the older skis?


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[racerxxx]

Nope. I'll post up later. First soccer game of the season shortly.

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[racerxxx]

OK, just gave it a quick once over.


When was the last time you cleaned the RAVE valves? Also, what exact oil are you using?

 

[yamaha188]

OK, just gave it a quick once over.


When was the last time you cleaned the RAVE valves? Also, what exact oil are you using?

I have not cleaned them since i got the boat about 1 1/2 ago, not sure when the previous owner did it last. I forgot to mention that i did take the caps off and they move very freely when i moved them. Would these open up and the partially close when running wide open? I have been running Mystik Jt-4 oil since i got the boat. Thanks for the Reply as soon as i get a chance i will remove and clean them just to rule that out. It would be sweet if thats what it was cause im pulling my hair out over this thing.

 

[racerxxx]

You really should pull and service them and clean them up. The front MAG RAVE will need to be disassembled before you can sneak it past the exhaust manifold. Nothing will drop into the engine. If you want to post some before and after pics that is great.

 

[yamaha188]

You really should pull and service them and clean them up. The front MAG RAVE will need to be disassembled before you can sneak it past the exhaust manifold. Nothing will drop into the engine. If you want to post some before and after pics that is great.

Ok pulled and cleaned rave valves but still doing the same thing. Sorry cant get the before and after pics to load from my phone. They really weren't to bad, had a little carbon on them. I also ran the fuel lines (where the go into carb) from one motor to the other but left the pulse lines connected to the motor they were on. Started both motors and revved them up together and still got the surge on the same motor. This really acts like a fuel issue but im wondering if it could be electrical, just dont know what to look at next.

 

[racerxxx]

On the front of the mag housing on an aluminum bracket is the rectifier. Just undo the plug and see if the problem goes away.

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