- Location
- Ontario
Hey man I just bought this ski did you ever find out bottom end power. I was not able to to test ride so wondering if should get a different prop
- Location
- the jetski grave yard
Looks very mildly ported at a glance but if it's a 760 cyl, the port timing is too high for low end punch. If some knucklehead just did the main exhaust ports and no transfer work, nothing was gained on bottom and more may have been lost. My porting guru told me years ago to raise the transfers 2mm to increase torque on 760 cyl. I dont do porting myself. That prop should work ok. Just a guessing game trying to diagnose problems with vague symptoms .
wydopen
onthepipe
- Location
- Goleta the Goodland
Doubt it’s the impeller..that’s what I run and I can go from sliding on a wave to fully hooked up and launching a heavy superjet out of the water with a properly tuned motor..
That doesn't look like a 760 64x cylinder to me, it doesn't have the spots that you have to machine to fit girdle bolts and it doesn't have the little gussets on the intake side, probably a 61x cylinder, which means the people speculating about port timing are probably mistaken.
- Location
- Glenmoore pa
Has 65u stamped on pistons, so at a minimum, it’s 760 bore size, right?
Sure, you can bore a 61x to that size, probably what it is. It's also possible that somebody could have raised the ports on a 61x cylinder.
I was just pointing out that some people have jumped on the higher port height of a 64x cylinder as a possible explanation, and I think that is not a valid assumption, because it doesn't look to me like it is a 64x cylinder.
That impeller is going to be a little too much load but shouldnt completely kill low end. Last time I had the problem you describe it was an exhaust leak under the hood. I would check compression, ignition timing, and exhaust port height. Less than stock timing will hurt your spool up. as will a high port with low compression. But first prop the hood open or carefully ride without it, If it runs good you have an exhaust leak. Also open the top and bottom screw on the carb and note any changes. Too lean will make it sluggish.
- Location
- the jetski grave yard
Upon closer inspection, you are right, it's a 61x cyl 84mm 65u 760 pistons. Still, the ports look tiny. Not the ragged edge porting I'm used to looking at or want to see if i expect hp. Actually 65u are tripple pistons. 64x are 760
bored&stroked
Urban redneck
- Location
- AZ
If you have a 61x bored to 84mm and no bottem end power then something is wrong.
- Location
- Ontario
If it's a 6m6 can it even be bored to a 760 on the top end ?
- Location
- California
No. And even a 701 needs thicker sleeves. Group K used to do it on the 61X with thicker sleeves.
- Location
- California
I should have been more specific, not on the 61x cylinder. They did it on the 62T cylinder.
- Location
- California
Double post, Tapatalk being weird.
If you read the "f800 retro mod" article they go to 84.5 on the 61x cylinder with stock sleeves, it's a contradiction to other places where they say a 61x cylinder needs aftermarket sleeves to go 84mm. Somewhere on pwctoday there is a thread where somebody asks harry about the contradiction and he says it's because he thinks lower rpm milder motors are okay with stock sleeves at 84mm, but higher rpm higher compression motors aren't.
Anyway, this guy probably has 61x cylinders at 84mm bore, and it sounds like his problem is probably in the pump not the motor.
- Location
- California
Good to know, I was reading the 701 Big Bore section. I never get tired of reading Harry's pages. Just wish he would get back to updating the pages.
bored&stroked
Urban redneck
- Location
- AZ
Im glad I kept reading because I was about to post this. I was the guy who asked him lol.
- Location
- Ontario
Was able to take it for a ride tonight. Good news I love the way the hull rides. Bad news it has not bottom end power. I wanna keep it so my plan is go through everything and if all else fails get a jet maniac 718. Started tonight by opening up electric box . Has anyone use an aftermarket cdi like this. And shouldn't it a different cdi if it is bored to a 760?
Attachments
Quinc
Buy a Superjet
- Location
- California
Toss that thing in the trash and get an oem cdi. Next check that the stator is oem and not china junk and that the timing marks are lined up correctly.
Last edited: