Carburetor (specs) Database: SuperJet and Blaster 1

[fastgtfairlane]

Hello, looking for some advice on my current setup. I have great power from idle to 3/4 throttle, but from 3/4 to full throttle I have no increase in power

Peak rpm is 6900 @49mph

Brand = Mikuni
Model = OEM
Size = 44mm
Quantity = 2
Main Jet = 115
Pilot Jet = 120
Needle/Seat = 2.0
Spring = 95g
Pilot screw = 5/8
Main Screw = 3/4

62t/61x 730cc ported cylinder
Boysen intake
185psi head
Stock f/a with 2 screens removed
B pipe limited-(top,middle screws closed, bottom open 1/4)
Tdr waterbox
10/16 hooker prop
Protec exit nozzle
Stock cdi

Might consider an enhancer or a Zeeltronic programmable cdi to give a better timing curve and increase the Rev limit to better compliment the pipe, ported cylinder and higher compression. I think 44s are perfect on a 701. The limited chamber does sign off earlier than the mod chamber due to longer tuned length. Just for comparison, have you tried jetting the carbs to non reverse jetted? Something like a 120-125 Pilot, 125-130 Main with 22-25 psi? 6900 rpm is pretty good on a limited chamber. Factory pipe claimed 6700 with the limited chamber on a stock cylinder. Depending on the porting, max rpm may not increase much.

 

[Kjacob04]

Might consider an enhancer or a Zeeltronic programmable cdi to give a better timing curve and increase the Rev limit to better compliment the pipe, ported cylinder and higher compression. I think 44s are perfect on a 701. The limited chamber does sign off earlier than the mod chamber due to longer tuned length. Just for comparison, have you tried jetting the carbs to non reverse jetted? Something like a 120-125 Pilot, 125-130 Main with 22-25 psi? 6900 rpm is pretty good on a limited chamber. Factory pipe claimed 6700 with the limited chamber on a stock cylinder. Depending on the porting, max rpm may not increase much.

I have not tried reverse jetting yet but this thread has me thinking of trying it and seeing what happens. The main type of riding i do is chasing boats, jumping wakes, and bouy racing. It's currently great at 2 of the 3 but just lacks that full throttle pull that the rest of my friends skis have

 

[fastgtfairlane]

I have not tried reverse jetting yet but this thread has me thinking of trying it and seeing what happens. The main type of riding i do is chasing boats, jumping wakes, and bouy racing. It's currently great at 2 of the 3 but just lacks that full throttle pull that the rest of my friends skis have

You are running reverse jetting now which is basically a larger Pilot number than the main jet. So a 120 pilot and 115 main would be reverse jetted.

 

[Kjacob04]

You are running reverse jetting now which is basically a larger Pilot number than the main jet. So a 120 pilot and 115 main would be reverse jetted.

Whoops that's a typo. 115 pilots, 120 mains

 

[fastgtfairlane]

My ski being a pretty close setup as yours except I'm running a 148 pump and a tnt ss chamber vs the limited sj chamber and changing to the Zeeltronic cdi from stock was a huge improvement all over the throttle range. I believe the stock cdi limiter is 7-7100 rpm so if you're getting 6900 you're right at it. I think that is what is holding you back. The Zeeltronic limiter is programmable. Mines set to 8300. Also lightened the oem flywheel. I'm running the 760 zeel but there is a 62t version available now.

 

[kevbo]

I have not tried reverse jetting yet but this thread has me thinking of trying it and seeing what happens. The main type of riding i do is chasing boats, jumping wakes, and bouy racing. It's currently great at 2 of the 3 but just lacks that full throttle pull that the rest of my friends skis have

I.don’t understand why you are worried about pilot jet size when your complaint is lack of full throttle performance. Are you able to tune the top screw at full speed?

 

[Kjacob04]

I.don’t understand why you are worried about pilot jet size when your complaint is lack of full throttle performance. Are you able to tune the top screw at full speed?

I can get the motor to run rich and sputter at full throttle with turning the screws to about 1-1/4 out, it clears up and runs good at 3/4 turn out. I tried turning the high screws in as far as 1/2 turn out and there is no change in power or peak rpm so I backed them back out to 3/4 cause I didn't want to hurt anything

 

[MTRHEAD]

I can get the motor to run rich and sputter at full throttle with turning the screws to about 1-1/4 out, it clears up and runs good at 3/4 turn out. I tried turning the high screws in as far as 1/2 turn out and there is no change in power or peak rpm so I backed them back out to 3/4 cause I didn't want to hurt anything

Get rid of that water box or sleeve the stinger down. Your rpm is horrible for anything other than a stock 61x or the ski is way over propped
#1 with the right setup you can spin 7600+ and go way over 60 with a stock water box under 800cc
#2 #1killer of top end performance is over prop or lack of back pressure

set up like yours should spin 7200-7400 give or take. (With a proper water box or exhaust “system”

 

[fastgtfairlane]

He's got a STOCK CDI.

Probably hitting the Rev Limit at 3/4 throttle...

Per Group K "The stock SuperJet rev-limiters are 6500rpm (’90-’93 650s), and 7050rpm (1994+ 701s)"

My Square Nose SJ 6M6 Stock CDI consistently hits 6600 max and it doesn't limit revs as long as the Ski Pump is hooked up.

The advertised Nominal RPM Limit doesn't always match the Actual Rev Limit.

Plus that 10/16 Impeller is holding back his Top End too.

Install a CDI with a much higher Rev Limit and a 10/18 Impeller and he'll be going over 50 mph for sure.

Exactly what I was saying haha. He could try a smaller outlet nozzle with the 10/16 and maybe pick up some top end mph as well. He said he had a protec nozzle

 

[Kjacob04]

He's got a STOCK CDI.

Probably hitting the Rev Limit at 3/4 throttle...

Per Group K "The stock SuperJet rev-limiters are 6500rpm (’90-’93 650s), and 7050rpm (1994+ 701s)"

My Square Nose SJ 6M6 Stock CDI consistently hits 6600 max and it doesn't limit revs as long as the Ski Pump is hooked up.

The advertised Nominal RPM Limit doesn't always match the Actual Rev Limit.

Plus that 10/16 Impeller is holding back his Top End too.

Install a CDI with a much higher Rev Limit and a 10/18 Impeller and he'll be going over 50 mph for sure.

I did have an msd cdi in my ski at one point but swapped to a stock one to see if that was the culprit. Ski pulled the same rpm

 

[kevbo]

I can get the motor to run rich and sputter at full throttle with turning the screws to about 1-1/4 out, it clears up and runs good at 3/4 turn out. I tried turning the high screws in as far as 1/2 turn out and there is no change in power or peak rpm so I backed them back out to 3/4 cause I didn't want to hurt anything

Excellent, your full throttle mixture is correct. Now your pilots need to be just rich enough to provide good throttle response, it will probably need to sputter a little at 1/4 throttle. Considering your impeller, the rpm and top speed are about right for a low port cylinder with a wet pipe.

 

[fastgtfairlane]

Excellent, your full throttle mixture is correct. Now your pilots need to be just rich enough to provide good throttle response, it will probably need to sputter a little at 1/4 throttle. Considering your impeller, the rpm and top speed are about right for a low port cylinder with a wet pipe.

Low port cylinder and a limited chamber is going to keep the rpm down a little as well. Be curious to see what a mod chamber would do here since it's an inch and half shorter.

 

[waxhead]

Low port cylinder and a limited chamber is going to keep the rpm down a little as well. Be curious to see what a mod chamber would do here since it's an inch and half shorter.

Mod chambers are down on hp by about 2hp, they don't rev as high or have the low end. I have tried it and with extensive testing just could not get back the rpm that was lost. I spoke to the guy who used to do a lot of dyno work at factory pipe and he said the fx1 chamber is 2 hp more than then limited and the limited is 2 hp more than the mod

 

[MTRHEAD]

He's got a STOCK CDI.

Probably hitting the Rev Limit at 3/4 throttle...

Per Group K "The stock SuperJet rev-limiters are 6500rpm (’90-’93 650s), and 7050rpm (1994+ 701s)"

My Square Nose SJ 6M6 Stock CDI consistently hits 6600 max and it doesn't limit revs as long as the Ski Pump is hooked up.

The advertised Nominal RPM Limit doesn't always match the Actual Rev Limit.

Plus that 10/16 Impeller is holding back his Top End too.

Install a CDI with a much higher Rev Limit and a 10/18 Impeller and he'll be going over 50 mph for sure.

I figured with porting and other mods at least he would have rev limit delete

 

[SMV RYDER]

I just bought her.. I was told she was jetted for 5k ASL and I ride at 8k asl.. I was hoping that the ski wasn’t going to be that far off jetting wise but she is .. I do understand I am loosing 24% of power just riding that high up but still need help.. any suggestions for jetting?

So jetting has been a little bit of challenge..
120 main 100 pilot 1 3/4 out on low speed and 2 out on high speed. I got a pop off gauge coming and 80 gram springs, shooting for 18 to 20 lbs on the pop off. It’s much better about still needs tuning, I am hoping changing the pop off spring will help with the transition to the top end. I also think I am sooooo over propped.. 14.5- 18 so I am looking for a 9/15

 

[Kjacob04]

Get rid of that water box or sleeve the stinger down. Your rpm is horrible for anything other than a stock 61x or the ski is way over propped
#1 with the right setup you can spin 7600+ and go way over 60 with a stock water box under 800cc
#2 #1killer of top end performance is over prop or lack of back pressure

set up like yours should spin 7200-7400 give or take. (With a proper water box or exhaust “system”

This does make sense, i had a stock bore 701 with 160 psi head before I built the new motor that is in my current set up and I had the same issue with the last motor with it falling flat on power and the only things that remained the same were the b pipe, water box and electronics

 

[Kjacob04]

Have you checked the Throttle Butterflies to see if they are synchronized and fully open at Full Throttle?

Adjust Throttle Cable as needed.

I've seen Pump hooked-up 7600 rpm on a B-Mod Pipe with a different Yamaha based Engine. It's not the Pipe...

A fellow Rider has a Pump Gas Limited 760 with 46 mm Full Spectrums and B-Pipe and is pulling about 7300 rpm and doing about 54 mph...with NO PORTING

Maybe the Engine has an Air Leak?

Yes, carbs are synced and the motor is a fresh build with 18 hrs on it. I did do a leak down test a couple weeks to be certain everything was good

 

[kevbo]

Have you checked the Throttle Butterflies to see if they are synchronized and fully open at Full Throttle?

Adjust Throttle Cable as needed.

I've seen Pump hooked-up 7600 rpm on a B-Mod Pipe with a different Yamaha based Engine. It's not the Pipe...

A fellow Rider has a Pump Gas Limited 760 with 46 mm Full Spectrums and B-Pipe and is pulling about 7300 rpm and doing about 54 mph...with NO PORTING

Maybe the Engine has an Air Leak?

A stock 61x cylinder doesn't have enough exhaust port area for 7000rpm. With a pipe, 62T cylinders run great. They just lose low end response faster than 61x cyls so getting the pump right is more critical.

 

[Kjacob04]

Update: after reinstalling my msd cdi and the stock waterbox my peak rpm increased from 6890 to 6970 at 49.3mph so a step in the right direction but I can tell my jetting is now off, or it was never right to beging with. From the testing I did, my pilot needs to be increased and the main jet seems rich. Anything over a half turn on the high screw and it loads up really bad. I settled at 3/8, didn't want to go in any further.

115 pilot
120 main
2.0ns
95g spring
1-1/4 low screw
3/8 high screw

 

[kevbo]

Tune the top screw using your tach on smooth water. Set it at the rich side of peak rpm. Then adjust the pilots, then recheck the top screws. I suspect your pilots are too small, how does it sound at 1/3 throttle? Each step in pilot size makes a noticeable difference. Mains aren't nearly as critical since you have the top screws to supplement that circuit. It may come to life faster with larger pilots and the top screws set at peak rpm but this can be dangerous for long full throttle runs.