Super Jet 701 hesitation

[alme7airbi]

I have my superjet 701 with high comp head, factory pipe, ride plate, intake gate,msd ignition and some porting Compression is 165 170. When I give 1/4 to 3/4 throttle it hesitate but when full throttle every thing seems fine. changed the cdi and the pop off pressure checked the carb every things looks good went to the sea today and it happens again same problem


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[kevbo]

Is this a tuning problem or a maintenance problem?

 

[JC-SuperJet]

What size Carburetors?

What are the Low (Pilot) and High (Main) Jet sizes? Needle Valve Size? Spring?

What are the Carb Low and High Speed Adjustment Screw settings?

What was measured for Pop-off pressure? Did the Needle Valve seal tight? Any bubbling or fizzing prior to pop?

Per Mikuni Manual, an issue from 1/3 to 3/4 Throttle Range relates to the Main Jet size.

Is this SJ new to you or have you owned it for a while and is just now having these hesitation issues?

Post a photo of your Engine Bay.

Is the Cylinder Head of the O-Ring type?

 

[alme7airbi]

I don’t really know the jetting on the carb they are 38mm the spring is 80 grams. I owned the ski for about a year. I gave it to a shop so they can rebuild the carb before this problem happened after a couple of month the problem started. Btw I am just 17

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[alme7airbi]

What size Carburetors?

What are the Low (Pilot) and High (Main) Jet sizes? Needle Valve Size? Spring?

What are the Carb Low and High Speed Adjustment Screw settings?

What was measured for Pop-off pressure? Did the Needle Valve seal tight? Any bubbling or fizzing prior to pop?

Per Mikuni Manual, an issue from 1/3 to 3/4 Throttle Range relates to the Main Jet size.

Is this SJ new to you or have you owned it for a while and is just now having these hesitation issues?

Post a photo of your Engine Bay.

Is the Cylinder Head of the O-Ring type?

Do the main jet size need to be bigger or smaller. And I am so grateful for your help


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[Mike W]

Do the main jet size need to be bigger or smaller. And I am so grateful for your help


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You need to figure out your jetting so we can help. Pull the carbs and see where you're at.

Before you do anything, study the Mikuni manual. It will help you tremendously to understand what's going on with your ski and how to fix it.

https://mikuni.com/pdf/sbn_manual.pdf

Here are the instructions for that pipe. It also has the jetting specs. I would remove that reed spacer as well. All it is for is clearance for your carbs/flame arrestors.

https://factorypipewatercraft.com/media/instructions/yamaha/701SJ03.pdf

 

[JC-SuperJet]

If the problem happened soon after that Shop rebuilt the Carburetors, then most likely the problem is rooted in the Carbs.

They should not have changed any of the Jets. If the Needle Valves were replaced, thay should have used the same Size.

It's possible that the Shop used inferior Carb Rebuild Kits.

The Chinese Imitation Copy Cat Knock-Off Kits are cheap but do not meet Mikuni Specs. The Elastomers (Diaphragms) are inferior. The Imitation Regulator Diaphragms deform and leak after a short time. The Regulator Diaphragm Center Buttons are not the right size. That affects the Valve Needle position and movement, and thus Fuel Supply flow and response.

The Genuine Mikuni Regulator Diaphragm Center Buttons are Anodized Red. The Imitations are plain Metal with no anodizing color.

Call the Shop and ask them what brand Carb Rebuild Kit they used. Ask them to confirm if they were Genuine Mikuni Brand Kits.

Did the Shop install new Needle Valves too?

Must only use Genuine Authentic Made in Japan Mikuni SBN Carb Rebuild Kits.

Zip Tie the Fuel Supply Line to the Carb, it's missing. Zip tie the Pulse line ends too, as needed.

 

[alme7airbi]

The Jett has 35 written on it

Does this affect?

Black spring


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[JC-SuperJet]

Definitely need two new Regulator Diaphragms because the one shown is stretched, deformed and has a tear.

The #135 Main Jets are good. The Black 80 gram Spring is good too as long as it's paired with a 1.5 Needle Valve Body.

What are the Pliot Jet sizes? What is the Needle Valve Body size marked on the bottom?

Replace the Bad Diaphragms. Get a Tachometer and tune the Carburetors.

Here are good working Jetting Specs courtesy of Jetmaniac:

 

[alme7airbi]

Update guys the jet ski worked properly after I put some silicon on the edge of the diaphragm, probably it was leaking

But now I have rev limiter issue it hits about 5-6k I think it’s msd issue


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[tomski]

I see you have the high performance reverse mounted diaphragm covers installed.
Also known as the speed reduction kit.

 

[Kohldanielzimmer]

Tom is trying (with great humor and diplomacy) to tell you your diaphragm cover on the left hand carb appears installed backwards.

 

[alme7airbi]

Tom is trying (with great humor and diplomacy) to tell you your diaphragm cover on the left hand carb appears installed backwards.

I know I just installed them temporarily cuz I was in a hurry when I realized that I installed it backward I kept it that way. And I didn’t start the jet ski


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