sbn tuning know how.............

[cameron da river rat]

you once told me a formula of how many turns out of the high speed adj =so many up on the main jet? does that make sense? in other words, say you turn your high speed adj out one turn, if you want to turn it in like sea doo carbs, how much more would you have to raise the high speed jet?

and a 1.5n/s, does it flow the max of "what" on the carb? the manual says there is no need to go bigger than a 1.5 except to achieve correct pop off. what exactly is it your flowing? is it the max the fuel pump can pump or the carb can handle, or what?

thanks................

[cameron da river rat]

Re: sbn tuning know how.............

well i found it under the search forums. you said that say a 125 main jet w/high speed adj turned in will flow 100% of whatever a 125 will flow.

if the high speed adj is turned 2.5 turns out then the flow will be approximately 150% or 50% more fuel.

is there a ratio like..................say for every 1/4 turn out is like bumpin the high speed jet up by say 5?

for instance..........................

a 125 main w/high speed adj turned 2.5 turns out flow the same as say a 187.5 but this is just a guess, which is 50% more than a 125 main. so it increases 62.5, or 10, 1/4 turns out.

so mathmaticly, every 1/4 turn out would be 6.25 richer on the main jet?

of coarse we are talking about flow and not math here but this is just a guess? does this sound right? say i have a 107.5 main and the high speed adj turned 1 turn out, i could slap a 127.5 main in and be ok? or does it depend on engine configuration and the such?

the reason i ask is, the leaner i go on the main jet on my modded 550sx, the better it runs, or the more rpm i get. but im worried about siezing a motor. it runs great with a 117.5 pilot, and a 107.5 main w/high speed adj turned 3/4 of a turn out but the rpms will fall off when the motor is hot. they will surge...................like it will get to full rpm, fade off by say 3-500rpm then come back, then fade again, then come back as long as i hold the throttle down. it wont sieze and i've held it down for about 5min.

what ive been doin is increasing highs one step up at a time and decreasing lows one step at a time as well but top speed has suffered tremendously but i have gained some low/mid along the way. i was told to decrease pilot as main is increased or the opposite..................is this true?

[Bill O'Neal2]

Re: sbn tuning know how.............

No, you are way out in left field.

The low jet size detirmines how much fuel CAN flow into the low speed outlet and the by pass holes. So, you cannot flow as much fuel as would be provided by a huge jet such as a 185 just by cranking open the adjuster. The 50% increase is only relevant to how much total fuel the low speed jet CAN allow through and into the circuits.

[cameron da river rat]

Re: sbn tuning know how.............

maybe i confused you with all my jibber jabber.
im not worried about low speed jet or adj. just wanna know how much more fuel per turn of the high speed adj is adding and/or if there was a ratio that i could use to close the high speed adj all the way in (like sea doo carbs) and just put a bigger main jet.


the second question was referring to what the mikuni tuning manual says. it says that a 1.5 n/s flows the most the carb can handle. i was just wondering what flow are they refferring to? total carb carb fuel flow with biggest jets you can go and high turned out 3 turns?

[cameron da river rat]

Re: sbn tuning know how.............

is there a round a bout figure for the high speed adj for like, if you turn your high speed adj out 1/4 turn, you just increased fuel flow by 10%??
or for every 1/4 turn out you can just simply go up 5 on the main jet and get the same flow??? does this make sense? tryin to figure out how much more fuel you get by turning the high speed adj out.

[Bill O'Neal2]

Re: sbn tuning know how.............

I dunno, If you figure it out, let me know.

[Technical Support]

Re: sbn tuning know how.............

I remember some obscure text years ago, something like 3 turns=1 jet size...but don't quote me.

[dsolie]

Re: sbn tuning know how.............

TS,

I have always heard that exact same rule.. 3 turns is one jet size

[Bill O'Neal2]

Re: sbn tuning know how.............

The problem with that is, Mikuni says to never turn a adjuster screw out more than 2-21/2 turns maximum. Beyond that, there is no additional gain in the amount of fuel getting delivered.

[Technical Support]

Re: sbn tuning know how.............

Oh definitely! I'm not saying to use the needle in lieu of rejetting!