Yamaha super jet 701 issues

[Ronniev72345]

I have a sn 701 superjet 61x engine. The ski has 150 psi compression in both holes, starts right up and revs with no hesitation. I took the ski out for the first ride the other day and it is anemically slow and does not get out of the water for anything. It seems almost like it’s running on one cylinder however I checked spark and I have perfect spark on both cylinders. I have heard these skis are very strong off the bottom end and run very well however this thing can’t get out of its own way. Any help would be greatly appreciated as I’m coming from 650sxs and not very familiar with superjets.

 

[WFO Speedracer]

Start with the simple stuff , replace the spark plugs and check it again, spark plugs will halfway foul out causing what you described here.

Past that I would pull the carb and take a look . a leaky needle and seat , bad main diaphragm or stopped up internal filter would cause this as well , you need to pressure test the needle and seat to be sure and that way you will know what the popoff pressure is .

Next time you put in the water , pull the choke and see if it takes off, if it doesn't turn the gas to off and see if it clears out right before it dies , then you will know whether it's running too rich or too lean and have a better idea where to start searching.

More info is needed so someone can help you , at this point it could be anything.

 

[Ronniev72345]

Start with the simple stuff , replace the spark plugs and check it again, spark plugs will halfway foul out causing what you described here.

Past that I would pull the carb and take a look . a leaky needle and seat , bad main diaphragm or stopped up internal filter would cause this as well , you need to pressure test the needle and seat to be sure and that way you will know what the popoff pressure is .

Next time you put in the water , pull the choke and see if it takes off, if it doesn't turn the gas to off and see if it clears out right before it dies , then you will know whether it's running too rich or too lean and have a better idea where to start searching.

More info is needed so someone can help you , at this point it could be anything.

Forgot to mention I put brand new plugs in it no difference. Checked the exhaust system for leaks and restrictions was all good. The choke was replaced with a primer. Even if the ski runs great on the hose and revs out, will it act different in the water if the carb needs to be rebuilt?

 

[Big Kahuna]

Removed plug caps, Cut wires back 1/2", take needle nose and see if you can pull any wires, If any pull out, cut back the length of the strand, try again, Dont pull hard, just gentle tug. If the strands are breaking down it will crank up and sound fine, but once riding, they start moving and will loose current.

 

[WFO Speedracer]

Forgot to mention I put brand new plugs in it no difference. Checked the exhaust system for leaks and restrictions was all good. The choke was replaced with a primer. Even if the ski runs great on the hose and revs out, will it act different in the water if the carb needs to be rebuilt?

Most defiantly, anything will run good on the trailer but not when it's under a load , the fuel demands go way up when under a load .

Also related to what BK said the spark plugs caps are also a known cause of misfiring poor running, if you have the black caps those are the ones that go bad , on the red plug caps I have never had an issue with one of those .

 

[fx1mark]

As WFO said, there is a filter on the pump side of the carb. It's a very fine screen. It's very common for it to get clogged and create the condition you are describing.

 

[orangefinger]

check your impeller, see if you got something sucked up or wrapped around impeller

 

[WFO Speedracer]

check your impeller, see if you got something sucked up or wrapped around impeller

Or a badly damaged impeller kicking the rev limiter off and causing severe cavitation , all it takes is one bent back blade .

 

[DylanS]

Any chance you have a video of it running on the water?