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Old 02-17-2006, 04:48 PM   #1
CFAmD7G OP
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Need help jetting my XR650R

Im sure everyone would agree that in order to make the pig purr, jetting needs to be spot on. Just how does one go about obtaining crisp carburetion?

Not being one to solve every problem that comes along with my MasterCard, I am determined (with your help) to set up my stock Keihin for optimum performance. My research on carburetor jetting in general has failed to yield specific information about how each component contributes to overall performance.

My overall aim here is realize how performance is altered when these three variables are changed.
  • Main jet size
  • Needle clip position
  • Pilot jet size
The Pig Pen site has a great section on choosing baseline carb settings for your altitude, temperature, and performance modifications. http://www.xr650r.us/jetting/
Which should get you close to the crisp responsive carburetion were all after. But how do I coralate what the bike is doing , bogging of idle forinstance, with which component needs adjustment or resizing? The Art of Fine Tuning!

Am I asking the imposibility here? Is someone able to explain the interelationship of jetting changes to rideability characteristics?
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Old 02-17-2006, 05:40 PM   #2
CMWoody
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Good guessing and only changing one thing at a time. I ended up with a 172 main, 70 slow, 3rd clip HRC needle with an opened up HRC style rubber manifold, uncorked airbox and the rear baffle completely removed. E-bay billit power tip btw. I also filled the air valve with RTV silicone to block her up.

Good reading here
For FCR carbs but still a good resource, many of the same principals apply.










I bought an Edelbrock $389
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Old 02-17-2006, 05:49 PM   #3
wickedsprint
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where did you find one for 389?
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Old 02-17-2006, 06:03 PM   #4
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Quote:
Originally Posted by wickedsprint
where did you find one for 389?
Correction $369 + shipping

Also picked up some IMS pro pegs from the same guy, had each in less than a week. Recommended.
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Old 02-17-2006, 08:17 PM   #5
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The stock carb has a little slow response at low rpm. The Edelbrook has a pumpshot adjustment and can be adjusted in place for jetting.
As far as the stock - one thing at a time. Run it rich rather then lean.
It's a great way to get to know the bike. Once your done with the carb you can dial in the suspension - that's what I am working now.
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Old 02-17-2006, 08:32 PM   #6
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Thanks CMWOODYS your link is a good read.

Did you RTV the air screw for extra protection in stream crossings? Why such a mod?
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Old 02-17-2006, 08:47 PM   #7
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Anyone know what jets Honda ships with?
(It's probebly a rich baseline)
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Old 02-17-2006, 09:03 PM   #8
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Quote:
Originally Posted by CFAmD7G
Anyone know what jets Honda ships with?
(It's probebly a rich baseline)
No, it's not. Ships with a 65S (way lean) and a 135 main (to compensate for the intake bungs and exhaust plug).

I settled on 68s, B53e 3rd, and 175 for sea level, or same + 168 at high elevation.
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Old 02-17-2006, 10:05 PM   #9
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NEDURO QUOTE:

I settled on 68s, B53e 3rd, and 175 for sea level, or same + 168 at high elevation.

I,m guessing your fully uncorked, do you run an aftermarket exhaust & or sideplate cutout?
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Old 02-18-2006, 05:26 AM   #10
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Quote:
Originally Posted by CFAmD7G
Thanks CMWOODYS your link is a good read.

Did you RTV the air screw for extra protection in stream crossings? Why such a mod?
Tightens up the engine's decel characteristics and not necessary. Here's another good bit of reading on the subject.

Also note the flapper on the choke plate. Its little springs are known to break, lodge themselves up close to the piston ring and score the crap out of the cylinder wall. Take it off, choke will still work.


See, it makes the Keihin happy.
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Old 02-18-2006, 08:26 AM   #11
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I'm at 6200 feet and I run the stock pilot, a 168 main and the needle clip in the middle position on the stock needle. Bike starts first kick now cold unless it is below about 30 and will ALWAYS start first kick warm, air screw is two turns out. Throttle response off idle is zero lag.
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