760 swap runs amazing, but the throttle is idle or rip your arms off.

A

allted

Location
cali
Looking for some advice. I love this new ski I grabbed in the winter but it would be perfect if I could get the throttle a little more linear. Feels like at about 1/8th throttle, it just goes berserker, straight to half speed. Literally nothing in between, it hops out of the water and goes no matter how carefully I pull the trigger. Don't get me wrong, the power is awesome, but it takes away some of that fun carving and cruising finesse. So starting to 1/8th throttle is perfect, it takes a huge jump up to like 1/2 speed, then the rest of the throttle works as expected. I do lots of 3/4+ cruising and that works great as well. Would love to have some throttle authority from 1/8 to 1/2 throttle.

91 square nose, 760 (62T, 64X), dual SBN44's (95 gram spring, #130 main, #120 low), 144 9/15 SB hooker, Factory pipe (tried changing the tune, works best with only the top open 3/4-1 the others closed).

Any ideas what I might adjust? Pop off, Low speed, heck maybe the reeds (white reeds anything like a dirt bike power band)? Otherwise, it runs great, so I am hesitant to just start tweaking without some sage advice.
 
DylanS

DylanS

Gorilla Smasher
Location
Lebanon Pa
allted said:
Looking for some advice. I love this new ski I grabbed in the winter but it would be perfect if I could get the throttle a little more linear. Feels like at about 1/8th throttle, it just goes berserker, straight to half speed. Literally nothing in between, it hops out of the water and goes no matter how carefully I pull the trigger. Don't get me wrong, the power is awesome, but it takes away some of that fun carving and cruising finesse. So starting to 1/8th throttle is perfect, it takes a huge jump up to like 1/2 speed, then the rest of the throttle works as expected. I do lots of 3/4+ cruising and that works great as well. Would love to have some throttle authority from 1/8 to 1/2 throttle.

91 square nose, 760 (62T, 64X), dual SBN44's (95 gram spring, #130 main, #120 low), 144 9/15 SB hooker, Factory pipe (tried changing the tune, works best with only the top open 3/4-1 the others closed).

Any ideas what I might adjust? Pop off, Low speed, heck maybe the reeds (white reeds anything like a dirt bike power band)? Otherwise, it runs great, so I am hesitant to just start tweaking without some sage advice.
Click to expand...
Sounds like it’s set up perfect :)
What do the ports look like on the cyls?
 
A

allted

Location
cali
HA! It is soooo close to perfect, that is why I have not just gone out and started messing with it the last couple of months. After riding my buddy's 1500 for a while made me think the only thing I like better about it is his linear throttle.

What do you mean about the ports? I have a cam that I stuck down there and all looks great but I was just looking for cracked reeds really. Not sure what else I might look for?
 
fastgtfairlane

fastgtfairlane

Location
Charlotte, NC
Agreed, it sounds like it's setup almost perfect. Might try a 10/16 hooker. That will load the engine a little more down low and might not make it so light switchy. How are the water lines plumbed? If you have a dedicated cooling line to the pipe, you could try 1/2 turn out on the headpipe which should soften up the bottom slightly and move the power up in the rpm range a little. Wouldn't be dramatic but possibly enough to soften it up slightly to make it better for cruising. It will be very difficult to tune a ski to have great power down low and up top. Usually have to try to tune it for one or the other.
 
DylanS

DylanS

Gorilla Smasher
Location
Lebanon Pa
Well the low speed adjustment screw is used to set idle so don’t try fixing anything there.
Pop off pressure is from just off idle to 1/4 throtlte and low speed jet is just off idle to about 1/3 throttle where the high speed takes over.
A engine package (intake system, short block, exhaust, etc) has a ideal jetting/carb setup that will make it perform at its best (safely) and you really shouldn’t be trying to adjust a power curve with jetting. You can go a tad richer or a tad leaner but you risk pushing it and you’re kinda putting a bandaid on the bigger issue.
I’m not saying that there couldn’t be some sort of fuel issue that’s causing it to act the way it’s acting, but the case might be that you have a motor that was ported and setup to behave exactly like it’s behaving.
I agree with changing to a steeper prop I think it would be your cheapest easiest way to tone her down a little off the bottom.
Not sure if you have dual/three stage reeds but you could try going to single stage, not sure if you’ll feel a huge difference.

I think youll regret it it.. the light switch feeling is the most fun part of riding a ski!!!!
 
Last edited:
A

allted

Location
cali
I did try the pipe, I did get a bit more running it hotter but running either of the other two screws was to detrimental. The bottom screw open 1/2 then 3/4 and neither of the others would cause some occasional hesitation.

Thanks for the info. It very well could be set up for this. Like I said not the end of the world, and beyond perfect for wake jumping. Just trying to have it all I guess.
I will take a closer look at the reeds to see what is in there.
 
DylanS

DylanS

Gorilla Smasher
Location
Lebanon Pa
allted said:
I did try the pipe, I did get a bit more running it hotter but running either of the other two screws was to detrimental. The bottom screw open 1/2 then 3/4 and neither of the others would cause some occasional hesitation.

Thanks for the info. It very well could be set up for this. Like I said not the end of the world, and beyond perfect for wake jumping. Just trying to have it all I guess.
I will take a closer look at the reeds to see what is in there.
Click to expand...
Any chance you have a lightened flyhweel on that bad boy? If that’s the case you could go back to a oem one might help out a little. What do you have going on in the ignition department?
 
A

allted

Location
cali
Oh, I did not think about the flywheel. I wonder....That would probably explain it all. If it is I would not want to swap it back. I was hoping for a easy turn a dial or swap a spring an lose no ride time. Flywheel could cost me a day and would not wan to lose power.

I was pretty sure all the rest was stock, just a swap, but maybe they did dive in a bit deeper when they did it. Ignition looks stock.

Time to do more pull-ups to be able to hold on to this little booger!
 
DylanS

DylanS

Gorilla Smasher
Location
Lebanon Pa
allted said:
Oh, I did not think about the flywheel. I wonder....That would probably explain it all. If it is I would not want to swap it back. I was hoping for a easy turn a dial or swap a spring an lose no ride time. Flywheel could cost me a day and would not wan to lose power.

I was pretty sure all the rest was stock, just a swap, but maybe they did dive in a bit deeper when they did it. Ignition looks stock.

Time to do more pull-ups to be able to hold on to this little booger!
Click to expand...
The power will make you a better man
Good luck !
 
bored&stroked

bored&stroked

Urban redneck
Location
AZ
My ski is also light switch, its adjsutable up to about 1/2 throttle then its all or nothing, which makes cruising at 3/4 throttle impossible. Very annoying. I'm hoping some jetting adjustments get the power linear for me.
 
A

allted

Location
cali
Okay this is good to hear. Nothing is particularly wrong here, just how the rippers are I guess. I am willing to give up some speed, but not pull, that is entirely too much fun.
 
W

waxhead

wannabe backflipper
Location
gold coast
kevbo said:
It is very difficult to cruise slow with big carbs and a good pipe. It will tend to be on or off. If you want it really smooth then install a set of OEM 38mm carbs and a stock Superjet pipe. You will lose some max pull and speed but the throttle will be very linear.
Click to expand...
You may die from boredom 5 minutes into your ride but it will be a smooth and relaxing death
 
A

allted

Location
cali
waxhead said:
THe fact you said it works best with the top open tells me your tune is wrong
130 low 110 high
bottom water screw open 3/4
Click to expand...
Interesting. I never had much fun tuning the old three jet 550's (BN38??) carb but these SBN's seem more straight forward. Not scared to give it a shot. You think the springs are about right?

It seems like a larger low jet would probably even this out a bit and the jump to the high circuit would not be so drastic, is that the thinking here? I am also assuming the smaller high jet is just to even it out since it will already be getting more from the low circuit. Sorry, just like to learn as I go. Feeling like if my low jet is too small, my needle valve is probably really far out. Can't wait to check that.
 
DylanS

DylanS

Gorilla Smasher
Location
Lebanon Pa
allted said:
Interesting. I never had much fun tuning the old three jet 550's (BN38??) carb but these SBN's seem more straight forward. Not scared to give it a shot. You think the springs are about right?

It seems like a larger low jet would probably even this out a bit and the jump to the high circuit would not be so drastic, is that the thinking here? I am also assuming the smaller high jet is just to even it out since it will already be getting more from the low circuit. Sorry, just like to learn as I go. Feeling like if my low jet is too small, my needle valve is probably really far out. Can't wait to check that.
Click to expand...
Have you tested the ski throigh the throttle range as suggested by the super BN manual? It will give you step by step instruction on how to tune your carb.
This will give you an idea of which way you need to go if any.
If you ride the ski and give it 1/8 throttle where you’re saying it goes bananas but keep it at exactly that throttle position what does it do.
 
fastgtfairlane

fastgtfairlane

Location
Charlotte, NC
waxhead said:
THe fact you said it works best with the top open tells me your tune is wrong
130 low 110 high
bottom water screw open 3/4
Click to expand...
How can you come to that conclusion over the internet? I guess my tune is off on my ski as well cause my bottom screw is closed and I'm not reverse jetted. Yet everyone that gets on my ski all say how dialed it is. Help me understand.
 
A

allted

Location
cali
No I have not done the exact tests. I absolutely will now though. Need this wind to calm down a bit, 15mph plus gusts makes things a bit variable.

Some days I go pretty far out to get a burger, so I do try the throttle for long times at all positions. I was looking for hesitations at various positions, Check the plugs, exhaust temps.

At the 1/8th mark I can hold it super steady and try to creep up to it and everything is fine, then it just jumps and goes. Beyond that it is fine as well throttle response everywhere, it just jumps from like 15 to 25 at that one spot. I need to put some marks on the throttle to have a look. Everything is pointing to 1/4 being a crossover point, I was pretty sure it was before that but might be 1/4.
 
A

allted

Location
cali
fastgtfairlane said:
How can you come to that conclusion over the internet?
Click to expand...
I will say everything I have read said the bottom screw is the one I should have been messing with and not the top, yet it made it worse. Enough so I took it all apart and made sure the ports were free flowing and all equally functional, so I do think Wax is on to something.
 
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