yes but no but.

[B B]

CV carbs on motorbikes !  I have just re emerged from two weeks of pure hell, trying to tune My nephews XS650 Mikuni CV carbs to run on individual filters.

  This will be the case on Most probably all  bikes with CV carbs but Yamaha XS2 650 1974 M reg. Straight off if your bike still has its original air box and filter set up my advice is DONT TOUCH IT.  Ok its ugly black and needs hiding but Cv carbs need the air boxes chamber and volume flow to let them function acceptably.

  the bike in question was a pile of parts he bought in a drunken ebay whim back in the winter, He did an ok job of assembling the bike he had a frame stove enamelled and resprayed the tank himself and it looked good Norton style pea shooter exhausts and it bursts into life and ticks over great, but try to ride it and it had big issues.

  He brought it to me with the carbs off and in a cardboard box.

 I set too stripped and cleaned them put them back on and it was no better i changed the pilot jets from 132s main 42 pilots to 135 mains and 45 pilots, ran better but still holding back.

  Seriously difficult to set up on the original filters he had, they were effectively blocking the carb breathers in the mouth of the carbs mikuni BS  38s. 

  Tried some more filters bought off EBAY uk these were better no restriction on the rubbers, and , after trying a couple more jet options i ended up at 135 main and 45 pilots and 2 1/2 screws out and a small shim washer under each needle. Only way i could get it running acceptably.

 If by me posting this i deter any wannabe tuners from chopping up the black airbox then thats is a good thing. I can only describe the faffing around with these carbs as frustrating verging on annoying , Believe me DONT DO IT run it stock on the air filter side cv carbs are a real pain to get running on individual filters.

 

 

[Paddy Galore!]

I've always ran on stock airbox, the air flow through a clean filter in no way impairs performance even when tuning, I had a kz1000j tuned to stage 3 , that's cams and carbs, and it ran well still with the standard filter, hp was up by 50%, to 120hp at the back wheel, it did involve removing the us spec head with the gas recirculation gubbins, changed the wheels to 17"rims the chain pitch, sprockets and gearing were changed to suit, we got 150mph out of her on the rolling road