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Faced with a carb choice: Which would you choose.

  • Thread starter Thread starter FLATout?
  • Start date Start date
While the BS carbs are larger, they give equivalent performance to the VMs

The differences between slide carbs and CV carbs causes the 26 VM/34 BS to give the same performance
 
FLATout? said:
Thanks to you Frank Z, I've been having a hard time identifying the exact model, however there's a chance that none of the parts on my bike came stock. It was kinda a conglomerate of three separate parts bikes, but to what extent I'm not aware.

In terms of the size difference between the VM26 and the BS34CV carbs. I've read that going to bigger carbs increases performance. In the article I'm using as a mod guide, the author says that going with 29mm 'smoothbore' carbs made all the difference. To me it seems that 34mm carbs are almost...too large. Being of a stock selection, will these large carburetors deliver a noticeable power gain over, say the VM26's?
Click to expand...

Don't judge the carbs by the MM size. They operate differently so comparing them on bore size is not applicable.
I would go 34 MM CV and rebuild them carefully. If you have stock exhaust and airbox stick to the published specs but use a 42.5 pilot jet. The float levels need to be precisely set, I had drive-ability issues with mine until I set the floats correctly. I tried the 40 pilot but could not get it to idle properly. The air screws provide a range of adjustment but the pilot dictates the range to start with. With a 40 it just wouldn't settle down.

I'm running a VH street pipe with standard carb settings (except for the pilot jet) and contemplating a move from 115 to 117.5. The only effect will be on WOT above 8000 RPM which I probably shouldn't be spending much time at. This thing cruises at 85 mph around 6000 rpm as it is. I'm going to make a float level tester from clear tubing and an adapter to the fuel bowls to verify the actual levels. Measuring out on the bench is OK but nothing beats actually observing how high the fuel is in the bowls.

CV versus VM threads are like Oil and Tire threads. Ask 8 people and you get 10 opinions.
 
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