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Old 06-29-2014, 02:52 PM   #1
docwyte OP
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Choke/idle issue on '06 KTM 640 Adv

I just rebuilt my carb and when we started it up, unless the choke was in the middle position it would just rev up to the moon. So all the way in or all the way out, super high revs.

Fuel screw 2 turns out, idle screw not touching (not engaged), 45 pilot jet, needle in the 3rd slot, 160 main.

Playing with both the fuel screw and idle screw didn't have any effect.

I've put the 145 main (that was in the carb before) back in and re-measured the float height. To my very novice eyes, the float height looks correct, at 14.7mm. I haven't put the carb back into the bike to see if the main jet changed anything.

Before I rebuilt the carb I was having an issue where if the choke was too far out, the bike would have an unstable idle and die.

This is the first time I've ever worked on a carb, I'm sure the bike is telling me what to do, but I don't have the knowledge to understand it.

Any thoughts? Choke cable is free, attached in the middle and I replaced the plastic nut that threads into the carb.
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Old 06-29-2014, 10:27 PM   #2
bmwktmbill
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Doc,
Replied aon the other thread, the key is slack at al the cables and careful tank replacement, especially slack on that choke cable.

There are inner cable threaded adjustments if needed.

bill
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Old 07-01-2014, 08:17 PM   #3
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Hey Bill,

So I adjusted the choke cable and the throttle cables carefully to insure proper slack. Of course that was with the tank off.

Choke plastic nut is carefully snugged down with a wrench. I've inspected both carb boots and they're fine, no rips/tears. I've taken the carb apart and put it back together again.

Still the same phenomenon with the choke. All the way on it works as it should. At about the mid point pushing it off the idle drops down to where it should be. If I continue to push the choke off, the idle will rise again.

I've verified that the throttle is all the way closed and against the stop with the throttle cables attached.

I'm also getting a lazy return to idle if I crack the throttle WOT.

Beginning to get a little frustrated...
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Old 07-01-2014, 09:30 PM   #4
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Doc, are you positive the jet needle on the slide is assembled correctly?

If you flip the tank around setting it on the frame backwards and to the rear on the frame with the seat off and connect a long piece of fuel line you can run the engine the machine with the tank 'off'.

That might help you see something.

bill

Beginning to get a little frustrated...[/QUOTE]
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'02 KTM 640 Adventure-lowered
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Cormack McCarthy-The Crossing

The faster it goes the faster it breaks.
And high performance=high maintenance.
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Old 07-01-2014, 09:59 PM   #5
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You mean the main needle with the clip on it? Yeah, pretty sure I put it back together like in the DIY Laramie wrote up.

Easy enough for me to check tho
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Old 07-01-2014, 11:01 PM   #6
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From what your describing, your engine for some reason has a lean condition at low throttle... The 2 indicators to this is that when your choke/enricher piston is partly on {making it richer} it will idle and the second is the rev hangup you describe when the throttle is dropped...

Now did the bike start doing this on it's own or was it something recent after you tinkered with the carb?

Several things come to mind that could cause this... - A blockage in the pilot circuit- Miss adjusted float height making for a low fuel level in the float bowl... An air leak into the carb/intake manifold from a poor seal or fitting...
Is the tip of your pilot fuel screw ok? With the screw out try blowing compressed air through the screw port to make sure it is clear through the pilot passageways..Try going from 2.25 turns to 3 on the screw to see if any difference is noticed... Make sure the hose from the fuel pump to the manifold is sealing properly, I once had a similar issue as you and it turned out to be causes from a poorly sealing pump to manifold bung vacuum hose...

You can run a clear piece of hose up beside the carb from the float bowl drain, crack the drain screw and see if the fuel level comes up near the bowl gasket level... Try a running test and see if the level in the tube changes much... If it is considerably lower than the gasket surface then something is amiss, either the float is set too low or something else

gunnerbuck screwed with this post 07-01-2014 at 11:11 PM
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Old 07-02-2014, 07:29 AM   #7
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Thanks for the tips Gunner! The bike has done this ever since I bought it, so nothing new. The fuel screw is new, I bought an extended one from Motolab when I rebuilt the carb. I didn't blow out the hole there tho, so I'll try that. Have a pic of the hose you're talking about?

The good news is the bike runs MUCH better with the 160 main jet vs the 145 that was in there before. Way more power, I easily hit 92mph on the freeway on ramp today and the bike was still pulling. So that's heartening as I felt the bike was always underperforming before.

Now if I can just figure out this choke/idle issue...
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Old 07-02-2014, 07:36 AM   #8
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Quote:
Originally Posted by docwyte View Post
Thanks for the tips Gunner! The bike has done this ever since I bought it, so nothing new. The fuel screw is new, I bought an extended one from Motolab when I rebuilt the carb. I didn't blow out the hole there tho, so I'll try that. Have a pic of the hose you're talking about?

The good news is the bike runs MUCH better with the 160 main jet vs the 145 that was in there before. Way more power, I easily hit 92mph on the freeway on ramp today and the bike was still pulling. So that's heartening as I felt the bike was always underperforming before.

Now if I can just figure out this choke/idle issue...
Just follow the hose from the fuel pump that runs to the side of the head, it slips onto a fitting on the right side of the engine head..
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Old 07-02-2014, 03:44 PM   #9
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Ok, I see it. Runs pretty close to the header. Looks a little crunchy, I'll check it out once the bike has cooled.

In a new development now it just wants to rev at 4000 rpm all the time. In between almost dying on me on the ride home from work. Awesome!
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Old 07-02-2014, 05:13 PM   #10
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Think you nailed it Gunner. Found a nice hole in the hose from the fuel pump to the head. I'll replace it tonite, hopefully that's the sole cause of this issue.
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Old 07-02-2014, 06:53 PM   #11
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If you cross the fuel pump to tank hose {white in picture} with the fuel pump to manifold block hose{black in picture} it will help hold it away from the exhaust...
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Old 07-02-2014, 10:41 PM   #12
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The Man

Hey everyone,

ROUND OF APPLAUSE FOR GUNNER!!

bill
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'02 KTM 640 Adventure-lowered
"On the road there are no special cases."
Cormack McCarthy-The Crossing

The faster it goes the faster it breaks.
And high performance=high maintenance.
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Old 07-03-2014, 11:15 AM   #13
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So there was a hole in that hose, then I found a hole in the other hose from the fuel pump that goes to the carb. Then I found the hose from the rocker cover to the frame had almost popped off the frame. Then I noticed a small oil leak from the hose from the frame down aft of the fuel pump and fixed it.

I replaced most of the hoses I could with new line and routed them away from heat.

Result! Bike happily idles at 1800 rpm with the choke completely off now. Took it for a quick spin around the neighborhood and it's running well.

Just need to dial in the jetting and fuel/idle screws now....
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Old 07-03-2014, 12:41 PM   #14
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Very cool !
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Old 07-03-2014, 03:26 PM   #15
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Oh yeah, I also cleaned up my GPS wiring, rerouted it to look cleaner, then I messed with the throttle grip, trimmed it up so the throttle snaps shut more cleanly and attempted to glue the grip on so it wouldn't rotate.

Kinda failed with the glue, I have to add more. Just waiting for my low fuel level sensor to arrive, then everything on the bike should be pretty good.

Gotta put some time into jetting tho...
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