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jet oriface sizes

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06 WR250 all mods done and more--drilled baffle of exhaust, gray wire on a switch i have done alot of jet changes when i bought the bike new i bought FMF power-up jet at the same time then found this web site and learned about the ais removel bought the gytr kit installed both kits except the gytr main jet the FMF kit uses a main jet adapter and the main jets are dynojet i keep going richer and the bike runs better and better benn told lately that oriface size may be the same but they flow diffrently had the dyno 155 and FMF needle with clip in the fifth groove from the end in bike it was running you better hold on tight GOOD power. now i have gone back to stock type jets they are alot easier to use -hex head- i put the 175 in but haven't gone riding yet and i am sure i will need to adjust the needle being a machinst i use my pin gage sets to check there sizes

jet list and sizes

stock keihin jets main

#165 = .063

#168 = .065

#175 = when i checked it i wrote down snug .089 i think it was .069 not sure

leak jet #70 = .026

#90 from gytr kit in bike didn't check size before installation

dynojet

#138 = .054 snug

#142 = .056 snug

#144 = .056 loose

#150 = .059

#155 = .061 snug

gytr and FMF needles using they are calipers and they are almost identical if there is any differance it is less then .005 anywhere on the needle

the stock needle is alot bigger in diameter

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update

added jet sizes

#170 = smooth .066

#172 = smooth .067

and yes the #175 snug .069

PILOT/slow jets

#40 = .015

#42 = .016

note these are all SAE #'s

PETE

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nice work, i presume the fmf main jets have a smaller orifice size due to the taper being different to the stock needle.

i have the fmf power up kit on my 06 wr 250 and i am curently running a 150 main with the fmf needle 2nd clip from top.

the bottom end seems fine but the midrange is a bit lacking. have tried raising the needle (richen mixture) but it made it worse.

i was thinking of trying the 146 main with the clip on the 4th from top.

anybody have any thoughts.

ps i ride at sea level - 600 feet temp is about 16degrees celcius average

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Jet fuel flow is not just a matter of orifice diameter, it also has to do with chamfer, length of the passage. The only way to compare jets is to flow bench them.

DynoJet uses their own design solely to be proprietary. You have to buy their jets if you use their kit. Yet another reason I would only by a James Dean kit.

If you had a bunch of the same brand jets and were not positive the size of them (say the stamped numbers had been polished off), using drill rod might make figuring out what was what

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William any thoughts on my idea of a smaller jet???

There is some overlap of the needle and main between 7/8's throttle and WOT. However, very few people ever actually run in this range. Once many get over 3/4's, they tend to just go on to WOT.

Normally, when a bike is jetted, first you set up the pilot circuit, then the main. Then you select a needle that works. In this method, to tweak the 7/8's area, you have to fiddle with needle diameter. Once that is right,you work on needle taper to set up the bike between 7/8's and about 1/4. Then you work on the needles straight diameter to deal with 1/4 to just off of idle.

FCRTuningguide.jpg

NeedleEffect.jpg

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William many thanks for the info, i rode the bike home today and found it missing in top gear when holding throttle at steady revs even when going uphill so the engine is under load.

this was not noticable when i had the neelde set at its leanest.

hence my query about dropping a jet size.

but having looked at your graphs it would suggest that the needle diameter could be the issue.

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175 mainjet it was too rich 175 is the stock YZ jet size i dropped down to a 172 main the top end is wow it keeps keeps pulling. the mixture screw was only a 1/4 turn open so i have went down one size on the pilot jet this past weekend after i went riding so i am excited and looking forward to riding this coming weekend the rest of the caqrb settings are as noted in the post i ride in the pheonix area around 1200 elevation

PETE

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well went riding Sun the pilot jet change did the trick to cure the problem with off idle now the problem is with the needle jet going to raise the e-clip two grooves i.e. lowering the needle this past winter i kept going richer and the bike ran better temps where 70 to 80 degrees now that temps are over a100 may be why i have been leanning the system this weekend the temps are to be over 113 that is alittle to hot to ride maybe next weekend again i am excited to go every ride the bike runs better and better after all this work on the bike i have a chance to get a YZ pipe i don't know if i want to start all over again with the jets ?

PETE

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i decided against the yz pipe there is no spark arrester well the neddle is at the third groove from the end done three rides since over 90 miles not tired after the rides the bike is so easy to ride best running bike i have ever had there are no flat spots in the throdle , the power band , very responsive i'm done tuning now adjusting the suspension before every ride and it is getting better it is so much fun riding a good bike

PETE

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there is a myth that a 120/100-18 is too much tire for a wr250

first ride today with new tires

maxxis desert it rear & maxxis si front

i'm in LOVE it was great

i have done a couple more custom mods with parts that i have made

so the bike even running better

my freinds question me after they ride it " thats a wr250 " and i smile "yup"

PETE

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one thing i don't think i have mentioned

rarely have i been in top gear wide open throttle for any length of time

so i don't need all the top end speed that the bike is capible of doing

so i dropped one tooth on the drive chain sproket

after doing that

doing 55mph on clear flat sand and the bike still had alot more

the bike is a blast to ride

PETE

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