silly question?

6 replies to this topic
  • thumperjohn

Posted October 02, 2004 - 08:27 AM


2004 XR650L
What carb. is on the bike?
Is it a CV ?

I am ordering jets from sudco and want to be sure...


  • roadcam

Posted October 02, 2004 - 08:59 AM


I wont be much help on this...but the CV stands for Constant Velocity, a carb design Honda has used for years on most of their applications,as far as I know...just phone your Honda dealer parts dept... they will know

  • BWB63

Posted October 02, 2004 - 09:53 AM


Yes, it is a CV Carb. and uses normal Kehin jets that you can get anywhere. Same main and pilot (just not the same size) as the XR650R or any of the othere bigger XR bikes.

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  • MotoChris521

Posted October 02, 2004 - 05:02 PM


Kiehien small round,stock exhaust -start w/158 main-52 pilot.Race exhaust try a 165 main-55 pilot w/needle shimed .040". :cry:

  • smashinz2002

Posted October 02, 2004 - 08:27 PM


The 650L does have a CV carb, which means "constant velocity". The carb has a diaphram on top of it, and a butterfly valve is controlled by the throttle cable. When you open the throttle, the butterfly valve opens, and vacuum from the engine sucks the diaphram up, pulling the carb piston upwards, allowing the fuel/air mixture in.
By contrast, all dirt bikes, such as the 650R, use a direct cable link from the carb piston to the throttle grip. So, when you open the throttle, the carb piston is physically pulled up by the cable and linkage.
I have no idea why street bikes and dual sport bikes use CV carbs, I guess it has something to do with emissions, but I'm not sure. Anyway, I hope this helps!
'00XR650R/uncorked/jetted/street legal
'04KX500/fmf gnarly/jetted/illegal

  • roadcam

Posted October 03, 2004 - 02:08 PM


Honda started the CV constant-velocity carbs in the late '60s, on the old CB450SS humpback street bikes, if memory serves me right ... the idea was to eliminate re-jetting due to altitude changes ... Honda's aim ws to build bikes that could go anywhere on a trip, and still run well ...

  • qadsan

Posted October 03, 2004 - 05:44 PM


the idea was to eliminate re-jetting due to altitude changes

Yep, and it reduces pollution, usually offers better MPG, etc. It's a great idea IMO for some applications, but it's not always the best choice, especially for serious off roading.

Conventional carbs have the throttle slide directly connected to the throttle cable, which connects to your grip. Everytime you twist the grip, the connecting cable raises or lowers the slide in the venturi. The throttle cable on a CV carb is connects to a butterfly valve as opposed to the throttle slide. This butterfly valve varies the volume through the venturi, but unlike a throttle valve, it's the pressure difference from the venturi to the outside atmosphere that moves the throttle slide. This helps out during changes in altitude, but if you were to go off a big jump or hit a section of rough whoops, the spring force holding the throttle slide in position may not be sufficent during these events and as a result the bike will momentarily bog. You may also loose throttle response in some situations such as if you encountered an obsticle where you suddently needed to lift the front wheel because a CV carb would have to wait for enough vacuum to build in the venturi before the throttle slide would fully open where as a conventional carb can open the throttle slide immediately upon twisting your wrist.

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