SN super jet questions

[trevangillette1]

So i've had this superjet for a few years. bought it off a dude while i still lived in San Diego. Rode it a few times. Got water in the engine somehow and then my dad replaced the engine a year ago. I've been riding it all summer and its been a blast but i want to get it running better and turn it into more of a freestyle style ski. i bought a worx 201 intake grate and a stock ride place and i'm going to do the d cut ive seen recommended here. I think i have some sort of extended plate right now, not sure if its any good or not.

Anyways my main problem is that my ski is running too rich. My plugs read oily and wet. It always takes a lot of cranking to get it to start up and primer doesn't seem to make a difference. I drain my battery cranking so much and usually i have to hold the throttle all the way down and send starter fluid to the carb for a cold start. once warm it always starts eventually with 30+ seconds of cranking. I checked today and my high jet was out 2.5 turns and my low was out 4.5. I assume i need to re-jet the carb since i'm at a much higher elevation (3700-5000 depending on where in the state i ride). Ive never re-jeted a carb before but i have done pop off pressure and cleaning on other mikuni carbs. I have a 701 with a single carb (not sure if its a 38 or what size). I have a Coffman aftermarket pipe but i really don't know what kind it is. everything i read online says ask the pipe manufacturer for jetting specs but i'm not sure what this one is called. can anyone identify it from my pictures? What is the best way to get my carb and engine tuned right. I assume i need a smaller jet for a more lean mixture? any advice? thanks!

 

[kevbo]

The bottom screw is for idle only, the top screw is for full throttle only. The idle mixture is easy to set, just start it out of the water and turn it in until the engine races then open it just enough to slow it down. They seldom end up over 2 turn out. The top screw is tuned at full speed on smooth water. Look for peak rpm then open it to slow it 20-30 rpm from there. If you have no tachometer just tune the top screw to provide the best full throttle acceleration. If the carb is stock the top screw will need to be opened 2-3 turns for the Coffmans pipe.. I recommend using a stock flame arrestor, the one pictured drinks too much water.

 

[trevangillette1]

Max Turns on the Adjustment Screws is 3 Turns. More than 3 Turns has no effect.

And if there are unscrewed too far out, you might end up with an Air Leak and the Screw backing out.

You haven't said if you Rebuilt the 44mm Carburetor with a Genuine Mikuni Kit. Also the Needle Valve could be leaking, flooding the Engine. Install a New Needle Valve.

I have a 650 Square Nose with that Coffman Pipe and a Flame Arrestor. Ride at Sea Level.
View attachment 428166View attachment 428168View attachment 428169View attachment 428170
#120 Pilot Jet at 2 Turns Out
#130 Main Jet at 2 Turns Out
2.5 Needle Valve x 115 Spring ~ 20 psi Pop-Off (Any Needle and Spring combo that yields about 20 psi Pop-Off will work)

This Jetting should work at your Elevation. You'll probably need to turn the High Speed Adjustment Screw IN somewhere between -1/8 and -1/4 Turn

this is some great info. Thanks! I pulled apart my carb today and found a lot of things wrong. first off my high speed aduster screw looks deformed as if it was tightened too much at some point. Also my needle has a similar type of deforming. it appears that i have a 1.3 needle and seat. I did a pop off test and it leaked air sort of bubbling almost immediately upon applying air but then didnt fully pop until about 48 psi... my main jet turned out to be a 135 and my pilot was a 115.

looks like i probably need to replace all those parts and get the pop off in the right zone. whats the best way to get these parts? most of the rebuild kits i see only have one spring which doesn't allow me to adjust pop off very well