Custom/Hybrid Tuning: staggered jets

[Vumad]

Tuning my x2 and curious about the range of staggered jets. I'm comfortable with tuning and my x2 is running very strong.

My question is about staggering jets. I'm currently 2 jets bigger on the back and possibly looking to go 1 more bigger in the back and one lower in the front, so 4 sizes different. 120/130. Is such a spread normal on a twin or does this possibly suggest an underlying problem?

Also curious if anyone staggers pilot jets. Is it done and how you you even know which cylinder needs more fuel or less fuel? Same goes for adjusting low speed screws differently.

Thanks

 

[yamanube]

Sounds like there is a problem, what makes you think you need to jet one cylinder different than the other?

 

[High Speed Industries]

Yamaha used staggered jets in the 760s. They ran a 135/137.5 for the mains. The rear cylinder was the one that got a little more fuel because they typically run hotter.
For your ski I would say you have some sort of an issue like an air leak. If your rear cylinder wants a ton of fuel I suggest checking your rear crank seal. How do your plugs look? Do they look the same even though you are running different jets?
I would recommend a pressure test of the engine and a compression test for good measure.

What engine is this on? What is your intake setup? Does each carb have its own pulse line? Are the pulse lines in good condition? Are they the same length?

 

[Vumad]

122 in both the front was black the rear was light. 122 front 127 back front plug same obviously but rear is getting a good color now and it's making more power.

I know some twins run staggered jetting, but 4 sizes of jetting is a big difference.

Going to change my cooling to move some more water through the back cylinder.

Power is very good. It pulls consistantly hard anywhere in the rpm range. No significant hesitation or bog, but I know I can clean it up a bit more.

 

[Vumad]

Yamaha used staggered jets in the 760s. They ran a 135/137.5 for the mains. The rear cylinder was the one that got a little more fuel because they typically run hotter.
For your ski I would say you have some sort of an issue like an air leak. If your rear cylinder wants a ton of fuel I suggest checking your rear crank seal. How do your plugs look? Do they look the same even though you are running different jets?
I would recommend a pressure test of the engine and a compression test for good measure.

What engine is this on? What is your intake setup? Does each carb have its own pulse line? Are the pulse lines in good condition? Are they the same length?

Just got called for our table. Get back to you after breakfast.

 

[Vumad]

Yamaha used staggered jets in the 760s. They ran a 135/137.5 for the mains. The rear cylinder was the one that got a little more fuel because they typically run hotter.
For your ski I would say you have some sort of an issue like an air leak. If your rear cylinder wants a ton of fuel I suggest checking your rear crank seal. How do your plugs look? Do they look the same even though you are running different jets?
I would recommend a pressure test of the engine and a compression test for good measure.

What engine is this on? What is your intake setup? Does each carb have its own pulse line? Are the pulse lines in good condition? Are they the same length?

Plug on picture, left front right rear.
Compression is 170/170, same as always.

X2, 96 big pin sts motor, dual 44 mikunis, k&n filters, dual pulse lines, r&d manifold, 3* reed spacers, stock reeds, stock motor, Ada head 170 psi, westcoast 650 manifold not ported, fpp a-pipe, Superjet limited chamber, rn sj waterbox, all 2" or bigger exhaust, stock electronics and flywheel. 650 pump with skat 14/19 big hub swirl prop.

I had the cooling set up where rear cylinder feeds the pipe which is adding some heat to the cylinder. Going to switch that. I don't think I have a case leak.

Edit: current jetting is 115 pilot, 127 main rear, 122 main front, 2.0 seat with 18 psi.

 

[High Speed Industries]

I can almost guarantee you have an air leak of some sort. Cooling won't do anything like that. The leak could be anywhere. Crank seals, base gasket, intake gasket, or even bad o rings on the throttle shaft. Maybe it's not an air leak, but it's a fuel issue of some sort.

 

[kevbo]

If both carbs are identical the difference between cyls should be slight. Normally one plug will be cleaner than the other. It was common for Seadoo 580-720 and Yamaha 701+ to have a hotter rear cylinder. I tuned two Kawasaki 750s that both had hot front cylinders. Factory 760s had a larger main jet on the rear cyl so the top screw ended up in about the same position as the front when both cyls are equal temp.

 

[Vumad]

Still tuning it some. X2 is my hobby so nothing gets done in a rush.

Switched the coolingso the front feeds the pipe and had some improvement in color.

Motor ran good the way it was with no significant hesitations or bog, but I felt it was too lean on the top and wasn't giving me everything it had.

Started switching around the low end circuits the other day, that is to say, I started richening up the pilot and leaning out the pop-off. Seeing significant improvements in power everywhere, and now both plugs are coal black at wot.

Made a video on the gopro but the card was full so it all got cut off. 50 on GPS ATM though.