drilling 5/32" holes in cv carb...details?

2 replies to this topic
  • motometal

Posted August 24, 2002 - 04:39 AM


Ok, I took my carb apart with 5/32" drill in hand, ready to drill holes as I have read about...but I chickened out!

Exactly which holes are supposed to be drilled out? I see two vertical holes with brass inserts, but it looks like it would make a real mess to drill these out...

can someone give me input on what works? Did it help?

I suspect most people also change jets at the same time, so it's not possible to give a true report on how much diference this made.

I'm afraid if the slide opens TOO fast I will get a bog, after all it isn't a pumper carb.

Also, I wish I better understood how this carb works. It appears that positive pressure, rather than vacuum, opens the slide.

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  • Jim_Scheide

Posted August 24, 2002 - 05:28 AM


Moto,if this is a XR650L CV Carb, drill the two holes in the vacum slider adjacent to the center hole where the jet needle slides through. This is in the upper part of the carb. You also raise the jet needle with a washer & go with larger jets (pilot & main).

  • motometal

Posted August 25, 2002 - 02:47 AM


update: I figured that out, it makes a lot more sense than to drill the holes in the carb body. Stock the holes were .113" and I drilled them to .125". I was a bit hesitant to go all the way to 5/32 which is .156"! This would provide almost double the flow, and at some point this non-pumper carb will develope a bog!

I couldn't resist the temptation, while I was in there I replaced the 50s pilot with a 58. I was out of room to adjust the pilot screw with the 50.

Between these two mods the bike barks noticeably harder when I suddenly get on the gas. Even with a street oriented tire on the back, if I have her leaned over in second gear (15/48 gearing) it tries to break the tire loose when I get on it!

How thick is the washer that most people put under the needle? Mine is only .023", I thought about adding another but not sure if it needs it. I know I am getting a lot better and removing and replacing the carb...no big deal now that I learned a few tricks!

[ August 25, 2002, 08:04 PM: Message edited by: motometal ]

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