HELP!!!! My cuyuna Jetski motor is on the fritz. Can you help me with this motor

[fishonboat]

I have a 1991 Tiderider Jetski that was manufactured by SOS marine. Ok here's the problem. The motor runs great at idle up to 3/4 throttle. At full throtle it almost seems like it's hitting the Rev limiter. I do know that is has one from looking in the service manual that I just picked up. Orgianly I tought that it wasn't getting enough gas to the carb at full throttle. So here's what I have done. I rebuilt the carb and the fuel pump that is attached (carb is a Mukuni BN38/34 round body style), replaced the fuel lines and fuel filter, Replaced the vacume line from the fuel pump on the carb to the crank case, freash gas mixed 40:1, new spark plugs and compression checked out at 140 even on both cylinders, I set the high speed needle at 1 turn out as it calls for in the owners manual and made adjustments in 1/8 increments to richin the mixture all the way out to 2.5 turns and it ran worse. Ran worse meaning that it bogged down at 1/2 throttle. Like I said it runs and starts great but at full throttle it misses like it's running out of fuel or there is air in the fuel lines. I did replace the fuel line with transparnet fuel lines so I can see there is no air in the lines. I have pulled the plugs after every adjustment to check there color and the factory settings on the carb needles seem to burn the best. The plugs are brownish black and dry. After flipping through the service manual last night I saw that there is a rev limiter. Now I'm starting to wonder if these things can go bad. I did have one person tell me that they think that the coils are breaking down. I tend to disagree. If the coils are breaking down I don't think it would run at all or it would run horrible. Any thoughts as to why this thing sounds like its hitting the rev limiter or running out of fuel? It's sounds and feels like a consistent miss. Thanks for your help in advance

 

[Jeff Walkowiak]

Re: HELP!!!! My cuyuna Jetski motor is on the fritz. Can you help me with this m

Re: HELP!!!! My cuyuna Jetski motor is on the fritz. Can you help me with this m

the plugs should be lite brown or tan run with the seat off and see if it runs better, you may have an exhaust leak that is killing your top end by pulling in exhaust fumes, also see if tour exhaust system is plugged up, any obstruction in the exhaust will kill top end, and you may have bad plug wires that are breaking down at high speed.

 

[fishonboat]

Re: HELP!!!! My cuyuna Jetski motor is on the fritz. Can you help me with this m

Re: HELP!!!! My cuyuna Jetski motor is on the fritz. Can you help me with this m

Thanks for the reply. I will pull the exhaust off this afternoon and check for clogs. I'm just baffeled by this. The plug wires are contect to the coils. The are one unit. I'm really trying to avoid buying a bunch of parts before check everything else out first. If I had an exhaust leak wouldn't I see black or oil or something inside the hull? The inside engine compartment is very clean. Thanks for your help. I will check this afternoon and post my findings.

 

[Jeff Walkowiak]

Re: HELP!!!! My cuyuna Jetski motor is on the fritz. Can you help me with this m

Re: HELP!!!! My cuyuna Jetski motor is on the fritz. Can you help me with this m

the wires are part of the coils but you can still change them if you have any talent. I use a automotive pushrod, cut the end off with a high speed cut off wheel, then notch teeth in the end. then I cut off the wire from the coil and carefully remove the remaining wire from the housing by turning the pushrod with a small pair of vice grips this removes the wire without harming the pin that goes in the wire from the coil as the push rod is hollow, I buy 8 mm wire from napa ,, SOLID CORE RACING WIRES, not carbon core.. then I put the wire in to the opening and superglue it in place, the plug ends just unscrew from the old wires so a little silicon spray on the new wire will let it screw on easily.. if you don't want to do it that way you can cut the wire about 3/4 of an inch above the coil insert about a 1.5 inch piece of paperclip in to the wire with half of it sticking out, then slide the new wire on to the piece sticking out and use superglue on the two ends to keep them together, slide a heavy piece of heat shring tubing over the conection and shrink it, after it cools put another layer of heat shrink over it again. it works great either way. to see if the wires are bad internally, unscrew the wire end and use a pair of needle nose pliers to pull on the metal wires if they feel tight you are ok if they pull out the wires are bad. as for an exhaust leak or obstruction it is a good idea to chech these as they can cause the problem you are experiencing and it will not necessarily show in the hull if it just started to leak.

 

[fishonboat]

Re: HELP!!!! My cuyuna Jetski motor is on the fritz. Can you help me with this m

Re: HELP!!!! My cuyuna Jetski motor is on the fritz. Can you help me with this m

Ok I think I have it narrowed down. I discontected the Rev limiter today and took it for a spin and it ran perfect. Can these Rev limiters go bad? I know what a rev limiter does and I know the reason for it but what is it? is it a computer or just a coil of wires or what? Also while riding it didn't seem like it was tacking out at full throtle. Like I said it ran perfect. There is no tach on this jet ski so I i'm not sure of the RPMs. Any thoughts? The manual dosn't give any was to test the Rev limiter. Thanks for everyones help