Super Jet help please before surf slam

[NVGuy]

I have an odd setup that don’t see much. I have a Polaris Octane hull, pump assembly, and exhaust(Factory B Pipe) with a Yamaha 760 motor that I just had bored out by Group K to 84.25mm bore. I live at a 5500ft. elevation as well. Below is what I have in it.

Lightened flywheel
Epic ignition with an aggressive stock stroke curve
Dual 46mm Mikuni carbs that are freshly rebuilt with a 130 main and a 100 pilot
New V-force reeds
Blowsion two piece head
MSD coil
Factory B Pipe with the bottom and middle screw closed and the top ¾ turns out

I have some more into it but can’t really think of it now…

My compression per cylinder is 160psi at my altitude.

I am having some tuning issues, I have recently got the low end somewhat runnable, but doesn’t have the pickup it should. It idles great (1200rpm) and my top end rips if it gets to that point (7500rpm). Whats weird about it is that you get to planning speed and give it full throttle, it will hesitate for about 5 seconds then go balls out and starts ripping. I ride with a guy that has a superjet that has a ton of stuff done to it. We checked his high and low speed needles and there about 1-1.25 turns out. Well we matched it with mine just because we were stumped, it feels that it is starving for fuel, well I turn up the screws to 2-2.5 and it starts getting better. My plugs look good a dark card board color. please help any suggestions will help. Thank you

 

[Vumad]

I'm no pro so don't over value my advice and hurt your set up.

However, read the mikuni tuning manual, it will help you.

What you describe sounds like a lean hesitiation. The high speed screws work from 3/4 to WOT. They will not correct your issue. The main jet works from 1/3 to 3/4 throttle. I would suggest you try going up 2.5 or 5 on your main jet and see how it runs. It runs better on the bottom because that is your pilot/popoff area.

Not to say that is for sure the issue or that I know what I am talking about, but going richer probably wont hurt. Follow the instructions in the tuning manual and check your plugs for leanness frequently.

http://www.mikuni.com/pdf/sbn_manual.pdf

 

[550headache]

sounds like its time to up your low jet a size or two

 

[iangdesign]

Get a couple jets a few sizes up and down from what you are sitting at right now for both high and low speed. Try them out accordingly. If it's hesitating, the circuit sounds like it is starving for fuel.

I am no expert either, this is just my experience.

 

[TheBuzzard]

if it doesnt hesitate as bad with the screw out 2.5 turns as opposed to 1.5 turns, the pilot jet is too small. to get the low screw back down to 1 turn, you are going to have to go up a bunch on pilot size. put 120s in there and screw the screw in to 3/4 turn out and ride/check it. since the low dumps gas even at WFO, you may need to lower the main jet, but that comes later.

 

[zachweb]

Not much elevation info here. I had a lot of trial and error to get my setup right at ~5000 ft.

I have stock 62t 701 with dual 38's in a 95 an.

Ended up with the stock pilot (70) but went from 130 to 122.5 mains. Set idle at OEM (7/8 I think). I'm about 3/8 turn in on hs needles and haven't quite hit the top yet, but...close.

Thing is, everything seemed to be right according to the manual, but I still didn't have the hole shot feel. I put on a 9/15 hooker (smaller pitch than I was running) and the thing just WOKE UP. Maybe the elevation was reducing the HP enough it wouldn't pull that prop!

 

[zachweb]

3/8 in from OEM on hs needles. Oh and this was a '95 sn.

5000' elevation shows ~ 94% jet reduction on the mikuni pocket tuner. Worked for me on the main jet...not the pilot though. Left that at sea level stock after trying all three sizes down to 62.5. 67.5 had a slight lean hesitation but I probably could have lowered popoff.

 

[NVGuy]

Sorry everyone I haven't replied to this but I have gotten my replacement jets and had lowered my pop off pressure that helped a bit but still had a bit of hesitation in mid throttle. I ended up hitting a wake and snapped my handle pole I will be done tig welding it today and be going out again this afternoon. Should I keep going lower in pop off pressure or do jetting still? Also could someone tell me what the stock pilot and main jets are?