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The TTR250 FAQ web pages -> TTR250 -> Carb stuff -> jet sizes yamaha / mikuni
Post Info TOPIC: jet sizes yamaha / mikuni
chrisstdt


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jet sizes yamaha / mikuni
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I have recently enlarged my airbox snorkel ,the bike is now running lean as i have uk standard 147 / 50 jets ,brian has suggested yamaha 150 / 52 but mikuni jats are cheaper and easier for me to get

 

So my question is has anyone got experience of mikuni jets and how they compare to yamaha jets or am i best to stick with genuine ?

 

Thanks



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TT-R250M


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First of all I would suggest to adjust the jet needle clip position to the lowest setting (closest to the sharp end). If that does not solve it then either try a #148 or #150. Bear in mind that if you have not done other mods (exhaust, air filter etc.) the #150 may be too rich for your set-up. If you are you running lean at idle-1/3 throttle a #52 pilot jet may be needed.

Mikuni jets are said to be ten sizes larger than Teikei, so a #138 Mikuni is the equivalent of a #148 Teikei.

I would suggest to find the genuine jets (if possible) as the Mikuni jets will not have the right taper for the needle and will affect performance. They also do not seal as they are a slightly different thread pitch, hence the ''squeaking'' when installed. The other option is 6 Sigma jets which are the same taper, flow rate and thread pitch as genuine but the pilot jet is slightly longer than standard (not a problem in my eyes).

Jarrah



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chrisstdt


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Sorry i should of said the bike has a twin air filter ,fmf power core rear can and needle clip has been lowered one clip ,ive got a trip planned late next week so i may of left it a bit late for this mod but its now running lean

is it worth dropping the clip again or with my mods will this likley not be enough ?

Thanks

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Terrence R


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I think you'll definitely have the go up in jets sizes. I purchased the 6 sigma jet kit from ebay. It came fast. I haven't installed it yet cause I'm in the process of making my ttr street legal, so I'll wait until after the inspection to put the air filter, pipe, and jet kit on.

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TT-R250M


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I would most certainly re-jet. With those mods I would suggest #52/#150.

Running lean can do irreparable damage to the engine as it will overheat causing excessive wear. In the worst case scenario it can burn a hole in the piston (goodbye bottom end). I would suggest that you get it sorted before going for a long ride.

Jarrah  



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chrisstdt


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Cant find the sigma jets over here so il see how quick i can get genuine ones

Thanks for your help

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TTRfan


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Ring Martin at MotoWard to see if he has them in stock, if not, try Fowlers of Bristol

This is what you need: 

JET MAIN (#150)Part Number: 2881432975

JET PILOT (#52)

Part Number: 43F1434226



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chrisstdt


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Tried fowlers and motoward and it would be tight as i need them for next thursday at the latest

My local yamaha agricultural dealer can get them for mid next week and i can collect them in work time !!

£22.50 inc vat not too bad smile



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TTRfan


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Result!  biggrinbiggrinbiggrin



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chrisstdt


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Thanks again for your help brian did the money for the other stuff come through ?

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TTRfan


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Yep - many thanks - just got the "Shopping" TTR through its MOT so will buzz down to the Post Office shortly.

Brian



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chrisstdt


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Great its always good when they pass biggrin



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chrisstdt


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Got the ttr delivered tubes and the new jets yesterday ,got the jets in last night and plugs a nice tan colour now

Almost ready for my weekends offroading in aryshire il try and get some pics

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TT-R250M


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Glad you got it sorted!

Enjoy!

Jarrah

 



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