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Rejetting R1 Carb Info

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    Mini Mad

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Posted 15 December 2008 - 03:13 AM

ok heres a short how to,for removal and rejetting r1 carbs including needle replacement

Step 1 remove carbs from engine and drain out fuel into suitable container via fuel feed pipe, some sort of box with 4 separate compartments is useful at this stage as you dont want to mix parts from each carb as you strip them as they are matched individually. get a tipex pen or something and mark the carb bodies 1-4 and the float lids too so you know which went where. Remove the 3 screws securing the float lids and place them seperately one by one in to your containers .

step2 heres the mainjet in its location ,the stock yamaha mainjets are size 130 which mean they have a 1.3mm hole .
Undo the jets carefully and either drill them to specific size or replace them with a more appropriate bigger mainjet. dont overtighten the mainjets after alteration as they will strip and youll cry. as your there you might want to check out the components inside for condition and integrity. replace the numbered float lids and redo the 3 lid retaining screws carefully.

step3 now one at a time ,remove the 4 black plastic vacuum chamber covers which are each held on with 2 screws. i numberd mine for fun. undo one screw then hold the cover down as you undo the second screw as under each cover is a large spring which just wants to fly out and get lost somewhere. put all the covers and large springs somewhere safe and now youll see the 4 delicate and easily damaged black rubbery piston valves inside each carb body.
youll notice what looks like a little o ring part of the rubber piston valve that sits in a small recess in the carb body,gently using something not sharp prise it out to release the piston valve from the carb body. put your finger inside the carb throat and youll be able to lift the whole piston valve and needle assembly out of the carb body.

step4 now the needles can be removed from the piston valves if your planning to change them or move them to affect the mixture setting. As youll see the piston valve comprises of 3 components its not necessary to remove the individual parts,its just been done here for clarity.
you can just see the grey plastic needle retainer inside the piston valve,using some needle nose pliers carefully pull it it will release itself and allow you to extract the needle assembly. Do this slowly as there is a tiny and anoying spring behing the grey needle retainer which will try to escape if you let it.
Now carefully withdraw the needle and spacer shims and place them down . the order of the spacer washers on the needle body is very important so make a note of what goes where before you remove them .Also notice the grooves on the needle and count them so you know where the circlip needle retainer fits.
IF you put the circlip retainer up a notch or 2 youll in effect lower the needle in to the jet and weaken the mixture ,If you put the circlip retainer down a notch or 2 youll raise the needles taper from the jet and richen the mixture.
I changed my needles over to slightly richer ones which meant i had to remove the circlip and transfer all the space shims over to my new needls so it helps to know what goes where !

carefully put the needle assembly with its shims etc back down the piston valve bore and locate the needle in to its recess. replace the needle spring and the grey needle retainer and push home.
refit the large piston valve spring and the vacuum chamber covers followed by their screws.
check everything moves freely and then relax !

this is only a short guide for further info refer to yamaha's maintenance manual.

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