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jet sizes .. i never noticed before ...
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Posted by: lee37vernon

i just got to looking down some jets as i'm gonna need to put a carb on my r shortly . the larger the jet number the smaller the diameter the hole ..... !!!
i know i've read it here before however would someone like to explain why you use a smaller jet when up sizing the carb ? i know something to do with air velocity . i never realised tho like i say that the hole got smaller as the number got higher , i would have thought the other way round which is why i'd like to know the theory behind it ..

Posted by: SET THE STAGE

maybe it's just on certain carbs because i'm almost certain the hole on my old blasters mikuni round-slide had a bigger hole with the a larger size jet

Posted by: lee37vernon

mikuni are probably different to keihin then , i know on the mikuni the numbers are way higher for a similar size jet to the keihin .

Posted by: fireburns99

are you sure???I'm almost postive that the size of the hole gets larger as the number does. The air velocity wouldn't have anything to do with the main jet. It just allows the gas to mix with the air. Maybe you have a special carb, and/or jets?

Posted by: GPracer2500

quote:
Originally posted by lee37vernon
i just got to looking down some jets as i'm gonna need to put a carb on my r shortly . the larger the jet number the smaller the diameter the hole ..... !!!
i know i've read it here before however would someone like to explain why you use a smaller jet when up sizing the carb ? i know something to do with air velocity . i never realised tho like i say that the hole got smaller as the number got higher , i would have thought the other way round which is why i'd like to know the theory behind it ..

What jets are you looking at? All the Keihin and Mikuni jets I've ever seen definitely have larger holes for larger jet numbers.

Posted by: 250R_4_ever

the Bigger the number the Bigger the jet hole

see by your self
they are classified from the smallest (152) to the biggest (200)

http://i22.photobucket.com/albums/b332/volks_r_us/jetbox.jpg

Posted by: lee37vernon

well thats bizzare ! ! carb came from a member on this site with spare jets .. did think it was odd when i looked .
dont recall drinking that much last night either

maybe i need glasses but i'll have another look , odd though !!!

Posted by: hang1p

maybe in England thats how it goes Don't you guy's drive on the other side of the road too. Over here in Maine bigger #'s means more fuel or bigger hole

Posted by: lee37vernon

i found out whats going on , i think !!

i have 7 spare jets with this carb , 155 , 162 , 165 , 170 .. you look down these and they are indeed sized as you'd expect ..

its then when you look at the other 4 things get weird , 210 , 220, 230 and 240 ... these are all way smaller than the first three , but bigger than each other in turn .

now i think these last 4 must be mikuni jets , i know that the numbers are way higher . when i think about it the member the carb came from does say he runs a 200+ sumething jet .. wonder if he's got one of those in his R ...

and HANG1UP , i do just what it says on the bottom of my driving license ..... ' TEAR ALONG THE DOTTED LINE '

Posted by: 250R_4_ever

wohhhhhhhhhhh

Bro you are confusing Keihin jets and mikuni which are NOT the Same

it's not because you have 280 mikuni main jet that a 180 Keihin main is gonna be smaller

mikuni and keihin are not gauge the same ways

mikuni will always a bigger number for the same size hole .That's how the rated there jets size

I didn't get first place cuz i didnt notice you where comparing mikuni main VS Keihin Main

btw they are not interchangeble

All 250r came with a keihin 34mm PJ Carb

Posted by: lee37vernon

i know this , this was not what i was saying .
my point was that maybe the jets i had numbered in the 200's which are SMALLER than the ones in the 160's etc are obviously not the correct keihin jets , i assumed maybe they'd be mikuni , as mikuni have a higher numbering system than that of the keihin .
however if they dont interchange then who knows what these jets are ?? they fit keihin but the numbers on them dont figure .maybe their cheap copies with dodgy numbers . anyhow their destined for the bin !!

Posted by: BLACKeR

could be from any jet kit, i way back in the day when i was dumber bought a K&N jet kit the numbering was completely different than what was in my stock carb, yet the jets fit fine.

Posted by: zedicus00

hey lee member when i sold you that i told you the jets over 200 were knock offs and would need to be redrilled if you wanted to use them? most performance shops can do that. though it may be cheeper to buy new jets, just depends on the shop... we get forget full in our old age.

Posted by: lee37vernon

i recall now , bit off on the old sizing though whoever made these were'nt they . lol .

destined for the bin for price of new jets

just threw me when i was looking at them deciding where to start my jetting at . thought i was going mad for a bit

Posted by: zedicus00

i cant vouch for your sanity but yes the jet sizes were a ways off... actually i compared them to some jets in the 140 - 150 range and they were pretty close.

Posted by: peeping TOM

quote:
Originally posted by hang1p
maybe in England thats how it goes Don't you guy's drive on the other side of the road too. Over here in Maine bigger #'s means more fuel or bigger hole

no m8 it's u american's who drive on the other side . ...lee keihin go up to 200 ,,,,,, got u mot yet ??????

Posted by: lee37vernon

waiting for oddments now , thats it . need me a pipe and seat latch and bits so it stays in 1 peice . soon as it turns up and i have it dialled in i'm off up the garage

Posted by: GPracer2500

quote:
Originally posted by peeping TOM
...keihin go up to 200...

Keihin hex head mains actually go up to 230. It's not especially common to see them past 200 though...

Posted by: fireburns99

yea i can't imagine the motor that would take anything more than 200. My stock bore takes a 190, and it's really built.