Jetting - erratic idle

XR650R uncorcked - stock CV carb

After pulling the carb for fun, then reinstalling it, the bike started to go to a higher idle at the traffic lights for a few seconds and then drop to it's original slower idle speed all ON IT"S OWN. When it goes high, if I blip the throttle it drops again.

I tightened the carb boots and that helped a little.

People say it's lean, and when I installed a more free flowing exhaust tip (leaning it out more) the erratic idle speed got even higher, and dropped less often to the slow idle.

Maybe this is a lean condition and I will wack the richer pilot jet in when I get it.................... Fuel screw has no effect. But if it is lean, then does that mean it should idle erraticaly - like fast for 5 seconds and slow for 3 seconds then fast again, ON IT'S OWN. It never did this before I pulled the carb. + my friend has same bike and setup without the problem.

Ever heard of this before?.....

It's not some crap in the carb blocking somthing up is it. I just think if it's lean then it's lean.............. but shouldn't it be stable.

no change with the fuel screw full in?

Im battling the IDENTICAL problem.. Im not getting any change when adjusting the mixture screw.. Bottomed out or 6 turns out, no change.. Then sometimes the idle will correct itself ?

I have a 68 pilot in the stock CV carb.. K&N filter (coming off asap) and uncorked stock silencer.. What you described are the identical symptoms Im having..

Add another one to the list! My xr has a mikuni flat slide installed, however it's doing the same exact thing. I checked for air leaks using the "spray ether" at the carb boot while running method. No change.

Burned, after an hour of fiddling I eventually got the bike to sound like it's about to stall at 1/2 turns out. And it didn't noticably drop idle at 3 or more turns out but that was at the lowest possible idle, is this the correct way?. So that tells me I could use a larger pilot jet. The trick was to first turn the idle as low as it can possibly go.

At what I'd call normal idle speed, I had mixed results with the idle dropping very slightly at 1 turns out and 2.5-3 turns out. The bike suddenly died a couple of times when going either way BUT died before the idle slowed- might be something else.

At higher idle speeds, the fuel screw didn't really have much effect. I noticed that a very slight turn of the idle speed screw saw the idle jump right up - and blipping the gas, made it drop momentarily.

I ended up setting the idle really low and going to 2 turns out, and then raising the idle back up with the speed screw and stopping before it got to that really sudden jump to fast idle.

Bike seems OK, but I can still feel a little jumpyness in the idle. I've basically lowered the idle to what I could live with - but still a little erratic.

Next to check plug, valves, air boots, carb cleanliness and gaskets, try 68 pilot jet. Any advice Burned.

Noticed that when I got off throttle completely whilst riding, the idle seemed a little lower.

Does the float level have any effect on idle? Does cutaway of slide have much effect. Is erratic idle from jetting or from crap in the carb or air leak?

is it possible that air could be getting through the diaphram due to a badly seated gasket?

My next theory is that it is this http://borynack.com/XR650R/xr650r_caruretor.htm the Air Jet Cutoff Valve(AJCV). Maybe if it is malfunctioning, it would explain the carburetor with a mind of it's own. The idle screw seems to be very touchy. Maybe at certain idle speeds this AJCV has some effect evn when just idling if it is damaged.

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Maybe I burnt a valve or two out ? while fiddling for minutes at a time with the bike at idle........ but I think I got it set pretty sweet for now until I get the larger pilot jet. No surging idle at the lights - but it's still not right.

Another, possibly unrelated, issue is (at some pilot, perhaps idle, settings) when I go full throttle in 4,5 gear at low speeds for 2 seconds, back off completely and then pull in the clutch......the bike's idle drops really low for 2 seconds, and depending on the setting I had, dies (especially if I give it a blip while it's low.) Seems to be better now with the currect setting but that pissed me off.

no,the pilot jet is too rich.

also those are not cv carbs.

i thought if it was twin cable throttle system and it's not a pumper then it's a CV carb.

What type of carb is the stock xr650r one?

I have a 65S pilot and they recommend a 68S after uncorcking. I am at sea level too.

I thought if it's a fuel (pilot)screw and you can't get the idle to drop by turning it out then you need the next size up. do you test the pilot screw at the manual's reccommeded idle speed or do you drop the idle speed right down to test it?

You have it backwards. If the bike still runs with the fuel screw gently bottomed, the pilot is too big, you need to go down a size.

I typically set the idle speed low enough for the bike to run without hopping on the ground and making piston slap sounds. I first see if the bike will stall with the fuel screw closed. Once I am sure I have the right pilot, I slow the idle speed down, then tweak the fuel screw for the fastest, smoothest idle I can get. Sometime, I further slow the idle speed down if needed and re-visit the fuel screw. Once I am satisfied with the fuel screw setting, I increase the idle speed to the recommended idle speed. I then carefully close the fuel screw, making note of exactly how many turns (to the 1/8th) it took. I then rest the screw to this number. Then I go for a ride. If decel popping is excessive, I might open the fuel screw a little more. Never have it more than 2.5 turns. If, during initial fuel screw adjustment, you have to set it more than 2.5 turns, you probably need a larger pilot or your existing one has debris in it and should be cleaned or replaced.

Thanks for the tips.

This from an XR650R website

Make sure your engine is fully warmed up and set the pilot screw to 1.5 turns out. Then with the 68s installed, turn the pilot screw clockwise until the idle slows. Then turn the pilot screw counterclockwise until the idle slows again. Make a mental note of how many turns you made in between the low idle points. Then turn the pilot screw half way between the low idle points to finish the adjustment. If you turn the adjuster counterclockwise and the idle doesn't drop down, then you need a larger pilot jet. If you turn the pilot screw clockwise and the idle doesn't drop down, then you need a smaller pilot jet. After adjusting your pilot circuit, re-adjust your idle speed if necessary.

I think my idle started to drop at about 1 1/4 turns out - it died at 1/2 turn out, and it didn't drop when turned 3 turns out or more.

It all started from pulling the carb and leaning the needle from 3rd clip to 2nd clip. I put the carb back in the bike expecting it to be fine and it began to surge at idle on it's own.

Installed a 65 pilot today and ran the screw at about a half turn before the idle was stable.. May need a 62?? ? Probably be fine when I get a stock filter on it..