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Old 04-10-2014, 05:14 PM   #1
bryantjt OP
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Location: Far Upstate NY
Oddometer: 1,081
2006 450 EXC Idle Issues

I posted this on KTMTalk as well but I believe there's more traffic here so:

My 06 450 EXC ran great last year when I put it away but it has 5200 miles and 180 hours so I decided it should be freshened up a bit. At the end of the season I was running the following:
OCEMP #5
42 Pilot
165 Main
Original Main holder
Original fuel screw with slightly stiff/dry o-ring

Over the winter I performed the following:
Replaced Baja Designs wiring harness and controls with Tusk/Sicass units (mainly to make more room on the bars and to replace corroded connections)

New main jet holder-Seems recommended to replace them around 200 hours?

New R&D Flex Jet remote adjustable fuel screw, came with new o-ring, spring and washer

Replaced the 165 main with a 162 main to see if I can rein in the fuel consumption a bit (high of 40mpg, low of 25mpg)

Potentially unrelated but the suspension was rebuilt by KTM World, all chassis bearings were greased, new throttle tube, new Motion Pro throttle cables, repacked the OEM muffler with Lexx premium packing.


Last fall it had a nice steady idle and ran well. Now, the idle can be set, by ear, to be a bit higher than what a Japanese model would require and it will purr along fine for 5-10 seconds then it will burble/change pitch for a second and then go back idling fine, it essentially misfires once and then runs fine for a few seconds.

I noticed this before and after repacking the exhaust and started with the fuel screw out 2 turns. I just went for a 15 mile ride and halfway through I stopped and tried adjusting the fuel screw to even it out and turning it in helped some but I had it fully closed at one point and it was still idling, but faster, with a hesitation every once in a while.

I thought that it should kill the bike if I turned the fuel screw all the way in?

It runs great everywhere except idle so I'm thinking that the fuel screw or the pilot jet is the issue. So either the idle screw tip is too short, or my 42 pilot that worked great last season (potentially leaky oem fuel screw/oring?) is now too rich and I need to drop to a 40?

I only guess that it is too rich since it never idled down when I closed the fuel screw, it only idled faster and never quit. Opening the fuel screw more than 1 turn made the idle drop and would lower the farther I turned the screw.


On another, potentially related note, I find that I have gas coming out the overflow if I lean the bike over much farther than what the kickstand angle allows. I stopped on a ride to clear brush last fall and leaned it against a berm and it was a full flow out the overflow tube.

Could my float height being off mess with the idle circuit?
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Old 04-10-2014, 10:36 PM   #2
gatorgrizz27
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Carbs on these bikes are very fickle, and most of the RFS bikes don't have a silky smooth idle. I would start by putting a new plug in it and clipping off a bit of the spark plug wire, cleaning any corrosion out of it and the boot. Does it start easily with e start and the kicker? Does it need the choke to start, and for how long before it stays running without it? Have the valves been checked recently? Is your idle set high enough that the decompressor isn't activating? Enough free play in the throttle cable? Is it responsive when you snap the throttle when warm or does it hesitate or bog a bit? Lots of little things to diagnose.
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Old 04-11-2014, 05:05 AM   #3
v303x
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Pilot jet.

You can try to clean it with a thin strand of wire and carb cleaner. I recommend you get a new one.

Cheers,

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Old 04-11-2014, 05:46 AM   #4
bryantjt OP
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If it was the pilot it would be too lean, I fully closed the fuel screw which would lean it out further and it didn't kill it.
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Old 04-11-2014, 06:29 AM   #5
bryantjt OP
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Not upset that the thread was moved, but I thought "The Garage" was the appropriate forum? Just curious.


Quote:
Carbs on these bikes are very fickle, and most of the RFS bikes don't have a silky smooth idle. I would start by putting a new plug in it and clipping off a bit of the spark plug wire, cleaning any corrosion out of it and the boot.

New plug at the beginning of last season. I will look at it today though.

Does it start easily with e start and the kicker?

First start of the season it didn't want to start, but then again I also forgot to turn on the ignition Since then, yes easy starts via my leg or electric leg.

Does it need the choke to start, and for how long before it stays running without it?

Given the tiny battery (my rc cars have more capacity) I always set the choke when it's cold but I can turn it off almost immediately and it will stay running.


Have the valves been checked recently?

I'm due for a valve check (will do later today). I adjusted them when I got it at 111 hours and checked them periodically over the next 30 hours and they didn't move. I'm at 40 hours since the last check though.


Is your idle set high enough that the decompressor isn't activating?

I have the idle pretty high, with 14/50 gearing it won't go any slower than 8mph at idle. I don't have a tachometer though to know where it is for sure but it sounds like it's up near MX bike idle territory


Enough free play in the throttle cable?

I believe so, I have free play with the bars in any position, lock to lock and it takes a bit of a turn to make the rpm increase.

Is it responsive when you snap the throttle when warm or does it hesitate or bog a bit? Lots of little things to diagnose.

At idle, a quick twist will snap the rpm up about as fast as you can turn the throttle.
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Old 04-11-2014, 06:36 AM   #6
RideFreak
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Quote:
Originally Posted by bryantjt View Post
If it was the pilot it would be too lean, I fully closed the fuel screw which would lean it out further and it didn't kill it.
That's a little strange, it should stall the motor when fully turned in unless the idle is so high it's already well into the pilot jets range of operation.
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Old 04-11-2014, 06:38 AM   #7
bryantjt OP
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I didn't think about that, I'll have to see how high my slide is sitting when I get out there.
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Old 04-11-2014, 09:26 AM   #8
bryantjt OP
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Taking a lunch break from tinkering but here's where I'm at so far:

Intake valves had tightened but I could still rock them, adjusted them out to 0.005", Exhaust valves hadn't moved from the last time, still at 0.005".

Valve adjustment screw on the right intake valve had 2.25 turns of adjustment from touching the valve, to touching the rocker, or 2.08 turns of adjustment left when proper clearance is set.

Fuel level is about 2-3mm shy of the pen mark, which I'm told is the factory float height setting, see photo below:




Not sure what you can tell from the plug since I shut the fuel off before I get home and let it run dry typically but here's the plug:

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Old 04-11-2014, 10:24 AM   #9
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I just measured that pen mark and it's actually 16 millimeters not 8 millimeters from the bowl gasket, looks like the float height is quite high.
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Old 04-11-2014, 12:19 PM   #10
bryantjt OP
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So, I found the float was set about 4mm too high and the idle opening was about 3xs the 0.048" recommended base point. I reset the float height by blowing through the fuel line and watching where the float was when the air stopped. This got the float parting line to be parallel with the carb body/bowl joint.

I set the fuel screw (verifying first the correct position of o-ring, washer, and spring) to 1.5 turns out and reassembled everything.

I needed the choke to start it, but it's 50 degrees so that was expected. I was able to turn the choke off after firing and it idled on its own. I kept the idle up with the throttle until the radiators were warm. It was idling a bit low and I could hear a clacking sound so I slowly increased the idle with the idle screw until the clacking went away, less than a full turn.

I turned the fuel screw a half turn in either direction and I couldn't hear a difference so I went back to 1.5 turns and left it. It's back to purring like a big orange kitten again.

I did not ride it but I suspect that there may be a difference at large throttle openings considering my float height was so high?
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Old 04-13-2014, 06:52 AM   #11
bryantjt OP
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Took a 100 mile ride yesterday, mostly paved as the trails are still snowed in. It runs and pulls better than ever. It gets up to speed faster and sounds better doing it. Even with lots of heavy throttle acceleration and running 65mph +, my first tank returned 53mpg. On the return leg I was taking all back roads so I could stand most of the way (that seat is killer) and kept it mostly under 55mph so I'm curious to see what this tank will yield.

Thanks for the help in diagnosing fellas!
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Old 05-07-2015, 05:14 PM   #12
falcn
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Hmmm.

I think I will probably have to check my float height. Just off idle seems rich (like just cracking the throttle and trying to ride 10 mph in 1st), but everywhere else seems good after I rejetted and replaced the worn emulsion tube. Idle screw all the way in acting the same as yours was - not killing it when it is warmed up.
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