SN Superjet 701 Performing Oddly

[benspen]

Hello all, I am hoping that some of you might be able to to help me figure out what's going on with my Superjet.

Some background; My brother and I have nearly identical superjets, squarenoses with 701s, both have new hooker 9/15, both have completely stock 701s. I recently did the pump bearings, wear ring, intake grate (worx 201), prop, mid shaft bearings, motor mounts, and starter. So theoretically the driveline is perfect on my ski. I aligned it well (better than my brothers). and the compression on my ski is great (148-150psi). However, the ski is simply not as fast or explosive as my brothers ski. its close, but not there on acceleration or top speed. My ski also makes this whirring kind of sound from the mid shaft area, I originally thought it was weird cavitation, so I did an intake grate and it didn't really change at all. I am confused as to what this sound could be seeing as how all the driveline bearings are new and aligned. I would also like to note that the carbs should both be stock (jetting), I was worried about the high and low needle tuning but I honestly don't really know how to tune the needles properly without blowing them up. the screws are not out of spec at all. Curious to see what you guys think!! both skis have also had the coils, and batteries replaced. I have attached a pic of the plugs out of my ski. Thanks guys!

 

[Pro-pulsion]

I've had the whirring sound too, it was the jet pump bearings. Same situation as you, brand new Koyo bearings and for whatever reason they went south in only a few rides. I replaced them with a set of SKF bearings and got about 7 years out of them. Just changed them out this year because they were due. Stock carb tuning is pretty easy, stick to what the service manual recommends and you'll get it pretty much right on. Dual carb specs, high speed front carb (mag side) 1-1/8 turns out from lightly seated when screwed all the way in, rear is 1-1/2 turns out +/- 1/4
Low speed screw both - 7/8 +/- 1/4
Single carb I don't have the specs for, maybe go with the setting for the rear carb to start. You want a nice and clean idle, snap the throttle and no hesitation or bog, it should rev up and quickly return to idle with no holding high idle then tapering off, and no dropping below idle then picking up after a few seconds to stabilize. Once you have that tuned, pretty much that's all you need for stock. Leave the high screws at the stock settings on the rich side. Also be sure if you have duals that the throttle plates are synchronized. You need a proper vacuum gauge for that. This snail meter makes it easy, get the orange line to float at the same number per carb and they're synched.

Snail Type Syncrometer Carb Sync Tool, GERMAN, SK Model - Aircooled.Net VW Parts

The best carburetor syncronizing tool made for us to syncronize dual carburetors. Rather than measuring manifold vacuum via a restriction, it sensitively and accurately measures airflow WITHOUT RESTRICTION. This is the top quality GERMAN SK Gauge.

vwparts.aircooled.net

 

[benspen]

Hi, thank you so much for a well written response. I appreciate it. Sucks to hear the pump bearings are making the whirring sound. it was making that sound last season but accompanied by some vibration. I replaced them with all new bearings and the vibration is gone but some whirring is left (on the first ride). is this something I should worry about? Could it be robbing me of some power? The skis are both single carb, I guess I will do some tuning to mine and see if maybe I can get it to rev out a little bit higher (I think that's part of the problem.)

Also, I am going to put my phone in my pocket (in ziplock) next ride with a gps going to see if I can clock a top speed, does anyone have an idea what top speed I should be looking for? specs on ski are above. also any recommendations for gps apps would be appreciated.

 

[fx1mark]

I would tune the carb the same as your brothers.

 

[benspen]

Tried that as well, about 1/4 turn in on each H\L, got worried it was too lean. My ski is nearly 2 turns out on L and 1 5/8 out on H if I remember correctly. But I set them to exactly what my brothers were at and didn’t seem to fix anything. It might need to go leaner. Will report back. Thank you