Main jet brand/size help!

[motomike07]

Hey guys

I’ve got an ’08 pitpro 140xr and I’m going to buy a bigger main jet for my carby (stock 30mm mikuni). I want to buy a 102.5 and 105 main jet, but don’t know what brand to ask for?

I’ve read in similar posts that mikuni and keihin have totally different sizes and I don’t want to end up buying a 102.5 & 105 keihin main jet which would equate to something totally different for the mikuni.

Has anyone bought bigger main jets for their stock carby 140xr before? If so, what brand/size are they?

Any help would be sick as I’m going for a massive ride this weekend

 

[1fifty1wheel]

simple, ask for a mikuni jet, its a mikuni carb so wouldn't it make sense? i don't know of any jets that are interchangeable between brands.
if your ordering a jet the person your dealing with should know what one to get by your description of the carb

 

[motomike07]

yeah but isn't the stock mikuni on the 140xr a fake? that's what i've heard...don't know if it makes any difference if it's fake or not though.

i'm taking the carby apart to night and taking the jet to the moto shop to get a bigger size so no biggie.

 

[DC125]

Good Luck MAn,


I was trying to do the same last weekend to my 140....

Spoke to a specalist and as the Mikuni Parts are hard to come by, best option is it buy a Keihan replica as jets etc are easy to come by and have a wide variety to fine tune.

Thats my suggestion anyway!

if you do manage to get Mikuin Jets and Needles, throw the info my way

 

[motomike07]

No worries man, i'll let u kno

im getting the oko 26mm keihin rep carby next week from maylands so could be in the same boat as you.

 

[DC125]

Yeah thats the best way man!

That then allows you plenty of options!

 

[1fifty1wheel]

a mikuni fakie still uses mikuni jets

 

[themountain]

a mikuni fakie still uses mikuni jets

No , they doesen´t....they use Keihin Mainjets and oldstyle miku pilots!

 

[tormentandglory]

I don't buy jets, I buy drills. You can buy small drills in 0.05mm increments from sutton. A 105 main jet has a 1.05mm hole. A 120 main jet has a 1.2mm hole, and so on. Just drill the suckers to the size u want, and if u end up going to far, solder them up and start again. Easy.

 

[Fiddy@norway]

I don't buy jets, I buy drills. You can buy small drills in 0.05mm increments from sutton. A 105 main jet has a 1.05mm hole. A 120 main jet has a 1.2mm hole, and so on. Just drill the suckers to the size u want, and if u end up going to far, solder them up and start again. Easy.

Drilling and soldering jets is really not the best way to dial in a carb, it's time-consuming if you don't hit the right size the first time and you'll be screwed if you drill or solder your one jet wrong, then you still have to buy a new one. jets aren't that expensive either, take your old jet to a decent shop and they'll hook you up, if not you try another shop.

 

[themountain]

Drilling and soldering jets is really not the best way to dial in a carb, it's time-consuming if you don't hit the right size the first time and you'll be screwed if you drill or solder your one jet wrong, then you still have to buy a new one. jets aren't that expensive either, take your old jet to a decent shop and they'll hook you up, if not you try another shop.

if you are building your own 4valve engine drilling a jet is not an issue for him I think
Problem is that genuine MIkujets have a flownumber instead of diameter....

 

[Fiddy@norway]

if you know your stuff you can do anything, but if you don't got rock-steady hands and only your fathers used and abused drill and not sure on the size of the jet you need, it's best to leave the drill alone and get a few jets and experiment...

 

[Cactus Jack]

The guy's a fitter/machinist/welder/fabricator/engine tinkerer ..... (my trades) ..... He thinks exactly like one too ...... LOL .....

I'll give you guys a hint ... MOST machinery in industry isn't bought ..... it's one off hand fabricated and machined by guys who are trained in the above trades .... and even the bought stuff is made by one off hand fab'd machinery .......


I've talked about drilling your own jets and soldering etc in another post ...... you can buy what's know as number drills ...... they're used extensively by tool makers (fitter/machinists who make punches , dies, molds , roll forming equipment etc) ... The worst a soldered jet could do is put microscopic bits of lead in your fuel as it wears over time ....

You wouldn't try putting a jet sized bit in a big hand drill .... LOL ..... You'd use a cheap small 1.5 volt dremel or pin vise and yes .... it takes a steady hand , the proper lubricant , and the right drill speed ....

 

[Fiddy@norway]

of course you can drill and solder your own jets, and I don't doubt tormentandglory knows his stuff, but the guy posting the initial question might not be so experienced in either machining or tuning carbs, it might not be wise to advice someone not so experienced to go and buy drills, soldering equipment and so on, it's easier and safer to get a couple of different sized jets and swap between until you get it right. just my opinion though...

 

[cass38a]

The part numbers are N100-604 102.5 and N100-604 105 also know as "large round" Mikuni. You can buy them on line for less than $10 each