I am contemplating a carb switch in my XR650L. The options are going with the 38mm XR600 carb or the 40mm XR650R carb. I don't want to use the Mikuni flat slide as it a two stroke carb and I don't want to spend the money on a pumper carb.
In general, I understand that a larger carb will allow more flow in the upper rpm range. I also understand that a smaller bore will create a faster velocity and possibly more torque at lower rpms. My question is, considering the horsepower of the 650L (which isn't much, 32-35 I think) will I really notice the difference between the two carbs? Will the 38mm allow essentially the same top end speed of the 40mm or the stock 41.5 CV with airbox and exhaust mods only (no cams or porting) or is a 35 hp engine capable of taking advantage of the larger bore? Is there a way to calculate the effect of changing carb bore size?
For comparison purposes, the stock 41.5 has a throttle flap and from what I understand...that effectively reduces it to 40mm.
In my mind, the benefit of using the XR600 carb is the smaller size and better fit in the frame, better access to the jets, the theoretical increase in low end responsiveness, and best of all eliminating the CV carb. I would prefer the XR600 carb unless it will lose top end speed....and I do use it all.
Just thought I'd see what input I could get from Rich or others before resorting to buying both and experimenting.
In general, I understand that a larger carb will allow more flow in the upper rpm range. I also understand that a smaller bore will create a faster velocity and possibly more torque at lower rpms. My question is, considering the horsepower of the 650L (which isn't much, 32-35 I think) will I really notice the difference between the two carbs? Will the 38mm allow essentially the same top end speed of the 40mm or the stock 41.5 CV with airbox and exhaust mods only (no cams or porting) or is a 35 hp engine capable of taking advantage of the larger bore? Is there a way to calculate the effect of changing carb bore size?
For comparison purposes, the stock 41.5 has a throttle flap and from what I understand...that effectively reduces it to 40mm.
In my mind, the benefit of using the XR600 carb is the smaller size and better fit in the frame, better access to the jets, the theoretical increase in low end responsiveness, and best of all eliminating the CV carb. I would prefer the XR600 carb unless it will lose top end speed....and I do use it all.
Just thought I'd see what input I could get from Rich or others before resorting to buying both and experimenting.
