Question about 2000 Yamaha Xv 250 Virago S
Need to know what others are doing when changing their Yamaha route 66 (250cc) stock 16/45 sprocket to 17/38. Is there a main jet change that's needed? I shimmed the main fuel metering needle. This help with a stronger pull, but top speed fade around 68 mph. The transmission now feel like I have four taller gears instead of four close gears
Well, the trans feels like 4 taller gears because with your sprocket change you changed the gear ration and gave yourself taller gears. 1 tooth up front is like 2.2 in back. effectively you changed about 9 teeth. humongous gearing change. Its a 250 and does not have enough hp to pull hard up top.
You don't change jets for gearing per se'. You jet for motor and exhaust and climate. To see if you need to change jetting up top you do a plug chop. Run WFO throttle at top speed and hit kill switch(pull clutch in) then when you have coasted to a stop remove the plug and look at it. you need to see how the insulator looks. Look down at the base not tip. should be chocolate milk color in a band about 5-7mm. thinner or lighter then bigger main jet. darker or fatter then smaller main jet.
JUST FYI-Shimming the needle only affects 1/3 throttle to about 2/3 throttle.
You should probably try to put the 16 back on it will help the bike pull. Too tall of gearing IMO.
Posted on May 12, 2014
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Posted on Jan 02, 2017
order the part online... you will not be able to get the part from the local bike shop as an in stock part...hope this helps
Posted on May 13, 2009
You can get to 55 with and old Honda 90cc. Your 250cc should do 80 with no problem. Your gearing is backwards. The larger the rear sprocket, the slower you go. You have tried to compensate a loss of engine power with a gear reduction demanding more from the what little power the engine is putting out. Put the 45T sprocket back on and do some work on the cylinder head. Ethanol is famous for corrosion and your valves are proof of it. All your power and gas mileage are going out the exhaust pipe. Pull the cylinder head and re-seat the valves. This should get back the power that is missing. You didn't mention any smoking so the piston rings must still be good. The stock main jet is #110. The higher the number , the richer the mix. Go to a #112 or #115 if you need to but only after the valve job. Right now the main jet is not the problem and changing it will only mean even worse mpg.
I answered this question once but the answer has disappeared into cyberspace. FixYa has a problem with that occasionally. A “very helpful” rating for this answer? Thanks!
Posted on Jun 24, 2009
you should hav check the valve spec before taking off the head. now you have to reassemble it to check it. see if your over or under adn replace with the appropriate shims.
Posted on Oct 22, 2009
SOURCE: Yamaha SR185 1981 carb settings
Righhttt And I need some new brain cells, stock jet size is .075 float level in 17/64ths turn adjustnebt screws in till they bottom out lightly then turn one and a half turns out andthat should get it to run, otherwise go to the nearest library and check out the book for that modle. there is another adjustment for the venturi plates but don't remember the exact proceedure.
Posted on Nov 22, 2009
SOURCE: I need main jet size
The main jet size should be 2 wire drill sizes larger (measure to the closest wire drill size as a starting point) to start for a 4 into 1 exhaust system, There is no one size fits all, you start with drilling it out the 2 wire drill sizes (set is 1-60) and see how it runs. Do not go more than 2 drill sizes larger as a base line. I have done this on at least 5 of my Japanese bikes.
Posted on May 11, 2011
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