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Old 06-27-2013, 02:10 PM   #1
D0dja OP
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Joined: Feb 2003
Location: South Africa
Oddometer: 36
Cry A little advice please - carburettion problem KTM 640 Adv w Dellorto PHM 40

I'm mystified, and this freaking bike and its mystifying problems are REALLY getting on my nerves.

After lots of niggly problems on my 02 640 Adventure, I finally solved two big problems... leaking water pump seal, and then a cracked head.

While the head was (probably) cracked, I'd ordered in a bunch of jets from the UK, and got the bike jetted pretty well (I'm in Johannesburg, which is at 1750m/5500ft). But that crack in the head was not good. I s'pose.

Finally sourced a new one, and rebuilt the top end last weekend. Bike fired right up, first press. No oil leaks anywhere, water level steady... but the carburettion had gone out. I assumed it was because of the coolant getting where it shouldn't, but I just can't get it right.

It starts pretty well, idles fine. But as soon as you crack the throttle hard at low revs it just disappears -- no bang at all. Close the throttle again and it picks up right away. If you wind it up slowly you can get to full throttle - a bit down on power and hesitant.

I started with 45 idle jet (I think, little bastard fell out when I was changing it and vanished). I tried a 38, and a 34. The 34 I guess is right, because with the others the fuel screw did nothing.

I moved from the 72DR emulsion tube to a 68, no improvement.

I moved from 140 main to 138 main jet, no improvement. This size is weird -- for a 640 with a PHM 40 even at altitude this seems very small. I then tried a 158, and now it won't start at all. Which is weird, since it starts on the starting jet (a 60) and maybe the idle jet, the main jet should not come into it at all. I even tried bump starting it several times downhill.

So, masters of the thumper -- any advice?

I've pulled the carb apart, checked float level, everything looks reasonable inside, needle&seat is sealing properly, vents are clear, etc.
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Old 06-28-2013, 01:06 AM   #2
D0dja OP
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Oh great. Just for whatzit I checked spark... and there's none.

Either I bumped something putting the tank on, or something new has packed up.

-48V at the blue/white wire.

I get a spark jumping on the HT lead if I scratch a wire from the battery against the blue/white wire. Resistance through the primary appears to be around o.4 ohm, the secondary 16k ohm.

Please tell me the CDI is not packed up :(

I just want to cry now.
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Old 06-28-2013, 10:29 AM   #3
D0dja OP
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Relax everyone. It was just a connector I knocked loose. Ignition is fine.

* continues monologue *
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Old 06-28-2013, 10:47 AM   #4
gravityisnotmyfriend
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Location: ((kg*m)/s^2), IA, USA
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I have a 620 with the PHM 40 carb and my bike would miss at high throttle when I dropped from a 195 MJ to a 170.

Now, I'm 4000' lower than you, so my bike needs to be a bit richer, but yeah, a 145 seems really small.

I'd leave the 158 in there now that you've got your ignition issues sorted. That main jet isn't going to do anything to your ability to start since it's not dumping fuel at idle.
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Old 07-01-2013, 08:24 AM   #5
D0dja OP
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So the ignition problem was just the connector from pulser knocked loose. Phew.

Happy to say the bike is going like a beast. Whatever the weird problems I fixed, they fixed something but good. My bike was jetted at sea level on a dyno with a 140 main. Pretty sure it's because the useless mech did not pick up that the pulser coil was getting dodgy.

It's now on a 162 main, and pulling strongly.

Starting well, idling smooth, going like stink. Went for a couple hours ride on and off road on the weekend... no leaks, no oozes, no drips.

Still needs more tuning ... the idle jet is being weird. Gone from a 38 to a 34 because the fuel screw was doing nothing... now if I turn it out even slightly it dies, suggesting it's too rich. But it pops a hell of a lot on the overrun until it's really warm, suggesting it's too lean.

But baby steps :)
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