Help with Jetting

yamaha415

yamaha415

Well guys i have to mess with a area that scares me. Jetting! My brother bought a 1996 SJ set up to run at about sea level. So here is what its got. ADA head with 33cc domes. Factory type 8 pipe, r&d intake, 44mm buckshot carbs, v-force reeds. We do most of our riding at about 2500ft.
Does anyone have a idea of what size the jets should be? Right now its getting way to much fuel. So if anyone had a idea what size i should start off with that would be great!
 
yamaha415

yamaha415

Hey Mike
Yeah i already checked that, but everyones elevation is from sea level to 700 feet. Thanks you though
 
M

marz831

Location
FL
Well, I hate to state the obvious, but if you KNOW you are getting too much fuel try stepping down both the mains and the pilots 5 points and see if it improves. Or, at least step down the pilots and see if that improves your low end. Unfortunately, carb tuning is nothing more than trial and error (unless the carb/engine builder gives you exact specs). Have you read the mikuni tuning manual? If not, read it. Then read it again.

What is your current jetting?
 
Kaveman

Kaveman

Born in USA(not Kenya)
Location
texas but soon tejas
Altitude and temperature changes necessitate changing usually only the main jet. Change them in the opposite direction you are going. IE higher altitude= lower main jet; lower temperatures=higher. Mikuni has good tuning guide that makes the tuning curve much shorter. I have one at the shop that I can check on Tuesday. Tell me what altitude the boat is set up for and about what temperature along with the main jet size. Also tell me what ambient temperature you will be operating in. Impeller pitch changes and compression changes may also need to be made. Dome changes are the opposite of altitude changes as well. IE higher altitude= lower cc's; lower altitude= higher cc's. Possibly a lower pitch impeller and/or higher compression. RMBC is good at setting his boat from Colorado springs down to sea level and back. :notworthy: Might be a good source of knowledge.
 
SUPERTUNE

SUPERTUNE

Race Gas Rules
Location
Clearwater Fl.
Buckshot carbs are really good as racing carbs under full throttle, but suck as freestyle/freeride carbs as the airspeed signal for the low jet is weakened and will need bigger low speed jets to get them to hit off idle, then that causes them to load up easy in freestyle. Get some stock aftermarket 44's or 46's and you will be a lot better off than those Buckshots, unless your racing wide open all the time...
 
2

2XLR8

X-
That is because they won't function unless they have low pop pressure. That is what causes them to load up. Sea Doos don't mind it but SJs do.
 
yamaha415

yamaha415

well i pulled out the 120 mains and put in some 107's. Just rode it around in my buddies pond for alittle bit, but still seems fat. Taking it out the the lake tomorrow to put it through the paces
 
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