Midwest Dualsport Motorcycle Community 

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 #8631  by Joe McBride
 29 Nov 2010 22:26
Hi: I wimped out and am staying off-road for the time being. I snagged a 2001 DRZ400E (electric start non street legal). It has the stock Keihin FCR 39(?). When I am riding and let off the throttle it does not drop down, acting like cruise control. Brake taps, clutch fans or throttle blips bring it down, but this is hairy on trails. I rejetted to correct specs for the Yoshi pipe. I turned up the air screw from (2 1/2 I think (on the bottom of the friggin carb) and it is still doing it. It has new throttle cables and throttle tube. What am I missing?
 #8632  by Savage
 29 Nov 2010 22:51
Does the throttle grip physically stay open?
Or does it snap closed and you have a hanging idle?
 #8633  by safiri
 30 Nov 2010 07:29
First, the screw on the front is a fuel screw. Out is more fuel, in is less fuel. (I read that the rule of thumb is if the screw is on the intake side, it is air and vice versa.) Not being picky, but if thought of as a fuel screw, then out makes more sense being more fuel.

The FCR is the same carb as on the KTM RFS bikes so I imagine any carb issues are common.

First, as Savage stated, check for physical hangups in the throttle tube (hand guard binding?) and cables.

Then:
- is the carb slide hanging up? Pull off the air filter and look in as you twist the throttle. The AP will squirt fuel, so glasses might be a good safety. Perhaps also do this with the bike running. Might need to remove the air filter housing.

- on the early KTM FCRs the throttle slide in the carb could be inserted turned 180o . The vacuum release plate needs to be on the front and a small hole (??) in it near the bottom.
- While there check that the main needle is being held down by an allen screw and that the clip is on the needle and that the grooves in the needle are intact.

- the pilot/idle jet may be dirty and you are actually idleing on the main.

- carefully pull out the idle mix screw (fuel screw) and check that there is a washer, oring, and small spring on the end.

Sudco has a very nice exploded diagram of the carb, as do the online KTM parts fiche at Cyclezone.

http://www.sudco.com/Carburetor01.html
http://www.sudco.com/Diagrams323728/fcr_exp.gif

BTW, a good primer on the FCR / FCRMX is here (Look at the stickied threads up top): http://ktmtalk.com/index.php?showforum=10

here is the link to a 2001 RFS, so the carb might be pretty similar:
http://65.57.254.60/shoponline/catalog/ ... 0310%2Egif
http://173.74.246.25/cyclezone/

http://65.57.254.60/shoponline/catalog/ ... 0310%2Egif
 #8634  by Joe McBride
 30 Nov 2010 18:57
Thanks guys. I will look at the diagrams later on. It is a hanging idle. It snaps back fine with not throttle tube hag up. When the air box was off fuel squirted the slide snapped shut. This was done only with the bike off. The air scew I messed with was on the bottom of the carb, not side. It did this when I first got it. One of the cables was broken and both were replaced with new. They seem to be working fine. The jets are new or cleaned/poked out clear. O-rings etc. were installed correctly. I willinvestigate the throttle slide postion, vacuum release plate and main needle. Thanks
 #8635  by Savage
 30 Nov 2010 19:15
Mine did that at one time. It would hang up for 3-4 seconds at a stoplight. It hasn't done it since I rejetted it. Probably one of the small jets no quite totally clean. I've read where others have cleaned, then just replaced the jet and that took care of their issues.
 #8639  by katbeanz
 02 Dec 2010 18:02
I'm not familiar with the FCR, but thumper carbs do wear out. My Mikuni got so bad it wouldn't idle down, but no visble wear on the slide. It had ten years and about 25k miles on it, so I think I got my money's worth. :mrgreen:
 #8669  by Hayden
 10 Dec 2010 14:21
You sure you don't have an air leak somewhere? Between intake boot and motor. This rubber takes on many heat cycles and becomes hard and Can shrink some. My KLK had a hanging idle that was fixed by adjusting the valves too. This could also be the issue. Check that if you don't know they are right. Spray some WD 40 around some joints on the carb and see if it sucking air somewhere. WD will kill the bike if it's sucking air. Hanging idle is usually a lean fuel issue which could be clogged jets like Mike said or sucking xtra air from somewhere it's not suppose to. This could also intail the choke cable/lever enterence to the carb. Let us know what you find.

Hayden