What do I need to do to make my 760 64x low end smoother?

[TehXshizzit]

Hey all, I'm running a 760 64x in my SN superjet with all the bolt on's. All the internals and carbs are stock

- B pipe (stock factory tune)
- high comp head (38cc)
- zealtronic ignition
- hot products filters
-10/16 hooker prop
- mag pump
- worx top loader
- op ride plate

I understand the 760s are more top end motors and believe me it screams at the top end. I can chase fishing boats, etc all day. But it seems like the low end just struggles sometimes till I can catch the R's then it shoots like a rocket.

Do I need to rejet my carbs or tune my b pipe a certain way to clean up the low end a bit? I understand I wont probably get that 701 snap but I'm sure I can get close?

Any advice?

Thanks

 

[jetx]

I would be looking at your pump...may want to try a bored nozzle and/or stubby cone in that solas pump. Maybe even try a 9/15 impeller

 

[maxboost]

I’d bore the nozzle some and see if that helps, if it does and your not cavitating yet try a freestyle pump cone. If that’s not enough then try re-pitching the impeller

 

[Jr.]

I know your plight well. The 760 port timing is very sluggish off the bottom.
But loves the scream up top. The only way to compensate without porting, is relatively high compression (200-205) and aggressive initial timing. ( you have Zeel listed? Easy to play with timing! Also try a TL flywheel mod) Both are not user friendly for a rec setup. Pump / prop tuning will help, maybe get you close to your goal? Look at your water screw settings on you B headpipe? Try top 5/8 open, Middle 1/4 open, bottom closed. 4mm restrictor into stinger.
I have developed a port map that does work for these motors. If you want to go to that level? Feel free to contact me to discuss??

Ski ya, Paul

 

[Half flip95]

Softer impeller, let it get on the pipe

 

[Quinc]

What jetting are you running? Might want to try reverse jetting.

 

[TehXshizzit]

What jetting are you running? Might want to try reverse jetting.

Stock jets - fronts 135 main and 1.5 pilot....rear 137.5 and 1.5 pilot. Everytime I ride I can easily do a 3 Mississippi hold on any part on the engine with no water sizzling any part if that tells you anything on temp.

 

[Quinc]

115 pilot? What is your pop off? You will need to lower it from stock when running a/m flame arrestors.

 

[OtherDonnieGuy]

Stock jets - fronts 135 main and 1.5 pilot....rear 137.5 and 1.5 pilot. Everytime I ride I can easily do a 3 Mississippi hold on any part on the engine with no water sizzling any part if that tells you anything on temp.

Does engine blubber at all like the choke is part on?

And/or Do you find that it's harder to get it back into the power after you back of the throttle for more than a few few seconds or let it idle back down for longer periods?

 

[bored&stroked]

I understand I wont probably get that 701 snap but I'm sure I can get close?

Any advice?

Thanks

Yes, listen to the countless people and engine builders who have said the port timing is much higher which is worse for low end. Its like asking a big cammed race motor to pull a suburban around with a stock stall convertor.

Smaller prop, more compression, more timing. All things that would increase power on a 701 as well.

 

[Roseand]

Stock jets - fronts 135 main and 1.5 pilot....rear 137.5 and 1.5 pilot. Everytime I ride I can easily do a 3 Mississippi hold on any part on the engine with no water sizzling any part if that tells you anything on temp.

You should never need to stagger front and and rear jetting on a standup. That jetting is set up for couches. If you search jetting here or go through the jetting thread there should be someone who has better specs for you.

I also agree you need to reduce pump load. With the higher port timing, stepping down your prop pitch will help it spool up faster.

 

[Storbeck]

You're probably going to end up somewhere in the neighborhood of 115 high, 125 low. I have a somewhat similar combination and I'm leaner than that, but I'm running the stock flame arrestor and a little bigger bore and some porting, so they'll be different.

 

[TehXshizzit]

Does engine blubber at all like the choke is part on?

And/or Do you find that it's harder to get it back into the power after you back of the throttle for more than a few few seconds or let it idle back down for longer periods?

Only time it really "chokes" out is when I don't time a wave correctly with the right rpms coming into it and I let off going into it and grab a hand full going up it. Sometimes it'll sit on its face.

But if I'm cruising, and jump on the gas sometimes I gotta pull the pole back like a horse and almost get the pump to shoot the preloaded water out and then I'm out like a rocket.

I need to take some new go pro video for you all this weekend.

 

[TehXshizzit]

You should never need to stagger front and and rear jetting on a standup. That jetting is set up for couches. If you search jetting here or go through the jetting thread there should be someone who has better specs for you.

I also agree you need to reduce pump load. With the higher port timing, stepping down your prop pitch will help it spool up faster.

I'm reading from the book on the jetting, but it was all stock so it should be true.

 

[TehXshizzit]

115 pilot? What is your pop off? You will need to lower it from stock when running a/m flame arrestors.

Should it be around the 30s like I've read or lower?

 

[Roseand]

I'm reading from the book on the jetting, but it was all stock so it should be true.

Listen to @Storbeck
Your jetting is not going to be stock. You added a pipe and you're running the motor in a standup.
The 760 oem 44s come jetted with a large main in the rear to compensate for the added load, which is not needed or helpful for your setup.

 

[Storbeck]

It's stock for the stock exhaust, compression, ignition, flame arrestor. All of that is much different on yours. Hesitation usually indicates lean on the low speed, and you're probably really rich on your high speed, but you have to actually do jetting on your ski nobody can tell you exactly what to run.

 

[Storbeck]

To clarify, you are running the 44mm carbs from the 760, right?

 

[maxboost]

Only time it really "chokes" out is when I don't time a wave correctly with the right rpms coming into it and I let off going into it and grab a hand full going up it. Sometimes it'll sit on its face.

But if I'm cruising, and jump on the gas sometimes I gotta pull the pole back like a horse and almost get the pump to shoot the preloaded water out and then I'm out like a rocket.

I need to take some new go pro video for you all this weekend.

I’d increase your low speed jet, I’ve had the same thing where it runs good but when you let off the gas then get back in to it quick it hesitates. Changing jets and seeing what works best takes some time but def worth it

 

[TehXshizzit]

To clarify, you are running the 44mm carbs from the 760, right?

Yes sir.