X2 throttle response

[ROTZINGER]

Hey guys! Out in Bacalar, México for the week and my x2 is acting strange. I was getting a runaway engine at wot when jumping waves so some of you suggested a crank seal leak (engine rebuilt completely on Jan 2020) so I pulled it out and although not super conclusive it doesn't seem to have leaks both in vacuum and with pressure. I took the carbs off (2 Mikuni sbn38) and didn't move any settings, after the tests everything got put back together and now it will not accelerate more than 3/4 of the throttle! It doesn't bog down or do anything strange, it just accelerates and after 3/4 of the way it will just stay at the same rpms...
What do you guys think is going on?

Thanks!!!

BR

Ps, I know I should change my flame arrestor, I know...

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[ROTZINGER]

This x2 has:
West coast head 190psi both holes
Custom intake manifold
West coast ex Mani and pipe
3° advanced timing
Skattrak 15 prop
Reed Stuffers
Dual Mikuni sbn38
The engine is still a 650 with stock pistons

FYI!


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[ROTZINGER]

Also sometimes you still get a runaway engine when doing bunny hops, I tried to open high screws but I only get worst fuel efficiency and oily sparkplugs....

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[wmazz]

The common cause for a runaway engine on any ski is a leaking carb
base gasket. I used to use special Snap-On open end wrench with
(I believe) a 15 degree offset open end on one end, and a 30 degree
offset open end wrench on the other end for dual 38's.

Dual 38's are difficult. A dab of loctite 515 gasket maker on the intake
manifold studs will work like a stronger blue loctite.

As for the acceleration problem, are you testing with a tachometer?

First I would look at the easy stuff, spark plugs and fuel filter. Possibly
water inside the tank. Check your fuel filler cap gasket.

But it sounds like how the straight pitch impellers pull. They accelerate
and then sign off higher in the rpm. About 5500rpm with a stock nozzle.

Your 15 degree impeller is too big for a 650. Even with a bored plastic
nozzle, I would be surprised if it reached 6000 rpm. An aluminum PJS
nozzle or PJS rip turn nozzle works well with the straight pitch impellers.

Either way, a 8/16 or 9/17 would work much better. Skat Trak made
3 generations of impellers before they got it right.


Bill M.

This is also the time of year that you need to open the high speed screws
at least 1/2 turn out compared to your jet specs you used during the summer.

Lean in the summer / rich in the winter.

Maybe the acceleration problem is the engine running flat with a tall impeller.

[ROTZINGER]

The common cause for a runaway engine on any ski is a leaking carb
base gasket. I used to use special Snap-On open end wrench with
(I believe) a 15 degree offset open end on one end, and a 30 degree
offset open end wrench on the other end for dual 38's.

Dual 38's are difficult. A dab of loctite 515 gasket maker on the intake
manifold studs will work like a stronger blue loctite.

As for the acceleration problem, are you testing with a tachometer?

First I would look at the easy stuff, spark plugs and fuel filter. Possibly
water inside the tank. Check your fuel filler cap gasket.

But it sounds like how the straight pitch impellers pull. They accelerate
and then sign off higher in the rpm. About 5500rpm with a stock nozzle.

Your 15 degree impeller is too big for a 650. Even with a bored plastic
nozzle, I would be surprised if it reached 6000 rpm. An aluminum PJS
nozzle or PJS rip turn nozzle works well with the straight pitch impellers.

Either way, a 8/16 or 9/17 would work much better. Skat Trak made
3 generations of impellers before they got it right.


Bill M.

This is also the time of year that you need to open the high speed screws
at least 1/2 turn out compared to your jet specs you used during the summer.

Lean in the summer / rich in the winter.

Maybe the acceleration problem is the engine running flat with a tall impeller.

Great insight thanks! Gave me a lot to think about... I just didn't understand the degree part in the bugging? What do you mean by an open socket?
Also temperature down here in mexico stays the same most of the year and I'm at sea level, do you think I must re tune for "winter" anyway!?

Thanks!

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[Bionic racing]

Check exhaust leaks or collapsed exhaust hoses too

[wmazz]

Great insight thanks! Gave me a lot to think about... I just didn't understand the degree part in the bugging?

What do you mean by an open socket?

Also temperature down here in mexico stays the same most of the year and I'm at sea level, do you think I must re tune for "winter" anyway!?

Are you using a translator program?

I used this wrench for dual 38's on the X2. Snap-On 13 mm Metric Four-Way Angle Head Open-End Wrench

Regarding the weather, I thought it was really hot and humid during the summer.
Possibly 100 to 120F (38 to 49C) with very high humidity. Apparently it can get
hotter in California and Arizona, than it does in Cancun or Bacalar. Humidity is
supposed to make a difference but I am not certain if it is enough to warrant
changing the jetting?


Bill M.

Sorry the picture is the wrong size (14mm). I didn't find a picture of a 13mm

[ROTZINGER]

Are you using a translator program?

I used this wrench for dual 38's on the X2. Snap-On 13 mm Metric Four-Way Angle Head Open-End Wrench

Regarding the weather, I thought it was really hot and humid during the summer.
Possibly 100 to 120F (38 to 49C) with very high humidity. Apparently it can get
hotter in California and Arizona, than it does in Cancun or Bacalar. Humidity is
supposed to make a difference but I am not certain if it is enough to warrant
changing the jetting?


Bill M.

Sorry the picture is the wrong size (14mm). I didn't find a picture of a 13mm

Jaja no translator, just bad spelling and big fingers on touchscreen jajaja sorry

It does get pretty hot (up to 35 in the summer) and omg the humidity (70-90%) from June to mid November. Right now we are 30°c with 65% humidity...

Regarding the wrench, what's it for? Where do you use it?

Thanks!

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[wmazz]

Regarding the wrench, what's it for? Where do you use it?

PJS dual 38mm carbs.jpg

[ROTZINGER]

PJS dual 38mm carbs.jpg

Ohhhh I see, I welded a stainless steel manifold for this so I don't use that mounting system anymore, maybe that's the problem... I'll give the carb screws a tightening just to be sure. I'll attach a pic.
The mating surfaces where milled after welding to ensure flatness.

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