carb or cable?


5 replies to this topic
  • redryder03

Posted May 20, 2004 - 12:31 PM

#1

New 04 xr650r uncorked with drilled exhaust, airbox gutted, new carb boot, 172 main and 68s pilot with new comp needle and jet, clip in 3 down form top. I am at 1100' or so and temps in the 70's right now. Everything works great and the bike rocks, the only small niggling thing I have is this just off idle .....sticking!!!!!!!! By that I mean it feels like the slide is stuck closed and all of sudden bang.. too much open. Just kind of a pain when trying to pick your way up a steep boulder covered trail and you have this slow slow slow and then to give it a little more fuel then bang tooo much throttle. I have adjusted the throttle cables to spec (1/16 - 1/4" play) and tried more and less play. Still seems the same. I also have adjusted the fuel screw and there doesn't seem to be any real difference doing that. Hmmmm. Any ideas out there? The plug looks real nice too. The fuel screw going in or out does not seem to be having any effect at all. Whats up with that? Part of the problem or an indicator of wrong jetting. Any ideas?

  • Winkel

Posted May 20, 2004 - 04:14 PM

#2

Remove your tank, disconnect the throttle cables, and actuate the carburator by hand. If you can still feel the 'sticking', then it's in the carb. If not, check for a kink in a cable, or make sure your throttle is not slid too far onto the bar. I've heard that can cause sticking.
Good luck,
Gary :thumbsup:

  • Old_Man_Time

Posted May 21, 2004 - 06:58 AM

#3

Did you install the new jet that the needle slides into upside down. It is possible.

Also when you routed the throttle cables make sure they sit above the tank mount and not below. They easily fall below the tank mount if you don't manually hold them above it while you slipping the tank on.

If the bike rpm does not change when you adjust the fuel/air screw, then your rpm (idle speed) is too high turn it down until the fuel screw does make a difference. Once the fuel screw is set properly you can turn your idle up but be careful not to set it too high or it will not immediately return to idle when you let off the throttle.
:thumbsup:

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  • JetPilot

Posted May 21, 2004 - 08:26 AM

#4

My 1993 XR600R is doing the same thing. When its running and I just try to crack the throttle, it feels like its a little stuck at idle but is free as long as its not right at idle. Strange part about it is it only does this when its running. The throttle totally free and smooth when its not running. I wonder if there is a vacuum that trys to keep the throttle closed at idle and dissapears as soon as its open a bit ?

  • redryder03

Posted May 21, 2004 - 09:36 AM

#5

My 1993 XR600R is doing the same thing. When its running and I just try to crack the throttle, it feels like its a little stuck at idle but is free as long as its not right at idle. Strange part about it is it only does this when its running. The throttle totally free and smooth when its not running. I wonder if there is a vacuum that trys to keep the throttle closed at idle and dissapears as soon as its open a bit ?


Sounds like exactly the same problem. I am leaning toward the vacumn theory too. Cables are routed correctly and everything operates real smooth when its not running. Also, it seems to take a little bit of a ride before I really start to notice it. Again, vacumn building up maybe.

{{Tim Sullivan posted this on another board also: hmmmm
I remember this problem before I switched to the edelbrock. As well as the not coming off idle problem to. I think it has something to do with the vacuum that holds the slide up against the intake side of the carb. Because when it was not running it operated very smooth. Just my2 cents. You can learn to live with it though. It’s not the end of the world. But if you got a spare $400.0 bucks I guarantee you will be happy with the out come

Tim}}}

But I don't want an Edelbrock....just yet anyway. Rather find the problem and fix it. I will check the needle jet to see if its in upside down, but I really can't imagine that happening, but who knows, stranger things have happened to me before.


:thumbsup:

  • heliosstudios

Posted May 23, 2004 - 06:31 PM

#6

Taking a stab in the dark, I'd say it's the way vacuum is used in these sliding-damper carbs. Absolute manifold "vacuum" is most at idle. Combined with the damper being at the most restricted position at idle, maybe the manifold vacuum is great enough to "suck" on the damper and cause it to resist movement. This then disappears as the throttle is opened because the damper moves up and vacuum drops. But it does feel "sticky" to me too ('94, Keihin.) I read somewhere about drilling out the three holes in the damper, but that sounds scary, like operating on yourself with a chainsaw. :awww: :thumbsup:

Pulling my Keihin out for the first time today, I was surprised to see so many vacuum hoses running here and there. (You'd think they could have made an automatic choke with one of those hoses but nooooo!) :lol:





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