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Discussion Starter #1
I've been in the process of setting up my FCR on my '15 XR650L and am having a heck of a time getting the bike to idle right and ride at low throttle inputs. Currently I have a 55 pilot jet and 85 pilot air jet (which is pretty big compared to other bikes with this setup) fuel screw ~3.5 turns, bike has a high flow air filter, and a powercore header/q4 muffler. I'm at 400 feet above sea level.
The idle will hang when revved up and sometimes I get cough back through the carb under 1/8th throttle. On the FCR i bought the TPS was missing, can air leak through the bearing where the throttle shaft sits? I sprayed propane at it when the bike was running and didn't notice any difference but I haven't been able to get a definitive answer on whether this will cause a lean condition.
Outside of the low throttle issues the bike runs like a champ! It'll pull hard anywhere above 1/4 throttle no hesitation, bog, or issues it's just that low speed problem that's got me pulling my hair out.
On the stock CV carb I had a 50 pilot jet in it and it seemed a little on the lean side. Do flatslides require fatter jetting than a CV? I don't have much experience with carburetors, everything else I've messed with has been fuel injected, but I've been dialing in pit bike carbs since I was a little kid.
 

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Sounds like you already know the problem.

The Pilot air Jet is probably too big.

Causing it to run lean, and the idle to hang.
 

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Discussion Starter #3
Sounds like you already know the problem.

The Pilot air Jet is probably too big.

Causing it to run lean, and the idle to hang.
Hey, I appreciated the response! That's what I was thinking. I'm not very familiar with the higher end carburetors or CV carbs, I've only really messed with small engine carburetors before this. The OEM carb didn't have a PAJ so I didn't really have anything to base the new carburetor' s PAJ off of. Originally the FCR had a 100 in it and I put the 85 in it which cleaned up my off idle respond alot.
I've got a 80 coming in the mail along with a 58 pilot jet. I'm gonna start by putting the air jet in and if I'm still having issues I'll throw in the bigger pilot jet.
 

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PAJ meters in AIR... not fuel.

You want a smaller one to richen it up.

Did you look to see what other people are running?
 

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Discussion Starter #5
PAJ meters in AIR... not fuel.

You want a smaller one to richen it up.

Did you look to see what other people are running?
Yea, I'm going down from a 85 paj to an 80. I haven't been able to find much about the air jet, it seems like most people kind of overlook it and just change the pilot jet. But most second hand FCR swaps I've seen come off of CRF 250's which run a 70 PAJ stock. My carb came off of the CRF 450 which comes with a 100 PAJ from the factory which might explain why I'm still having lean issues on a 55 pilot. Does that sound right? The 70 would be 3 sizes down from my current PAJ, most of the FCR swaps I've seen run between a 42 to 50 pilot jet. Would a 70 PAJ compared to an 85 make enough of a difference to step up to such a big pilot jet?
 

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It depends how much air that motor flows.

Some bikes use settings that make no sense at all on another, even with similar HP and displacement sizes.

On the WR450 I had, I disabled the ACV and put in a 100 PAJ, with a 45 Pilot... but with the ACV enabled, you need a 75? PAJ...

Like I said before, find out what others are running with that setup, it will be the easiest way to get it running right.
 
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