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Old 05-28-2009, 01:50 AM   #76
bmwktmbill
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Thai,
Sounds like you still have an issue with the carb. Look carefully at the arrangement of the parts on the main jet needle, there is a series of washers and clips that need to be correct. Make sure the idle jet isn't plugged, make sure the idle fuel screw has a spring and an o-ring.

All these parts are small and easily lost or misunderstood.

You can set the float height by attatching an old piece of fuel line to the fuel inlet and blowing on the hose, Flip the carb upside down and use your thumb to hold the float cage down square, blow on the hose and work the float up and down with your other finger. When the air stops and the floats are level you are set correctly. This sounds hard but it is really easy and exact.
bill
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Old 05-28-2009, 06:37 AM   #77
laramie LC4 OP
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Quote:
Originally Posted by bmwktmbill
You can set the float height by attaching an old piece of fuel line to the fuel inlet and blowing on the hose, Flip the carb upside down and use your thumb to hold the float cage down square, blow on the hose and work the float up and down with your other finger. When the air stops and the floats are level you are set correctly. This sounds hard but it is really easy and exact.
bill
never thought of that before. way to think outside the box!

i also think that he put something back in wrong, it happens when you first start doing this kind of stuff, it's called "learning".

laramie
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Old 05-28-2009, 10:04 AM   #78
stephano
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Quote:
Originally Posted by laramie LC4
never thought of that before. way to think outside the box!

i also think that he put something back in wrong, it happens when you first start doing this kind of stuff, it's called "learning".

laramie
I used that process too. Works great. I think it gives a more accurate idea of where the float level is.
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Old 05-29-2009, 12:22 AM   #79
bmwktmbill
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Step,
Yes the blow job works well on any motorcycle. The older airhead BMW's had twin carbs and you could set the floats without removing the carbs using that technique.

With my adventure I drain the gas out of the bowl, then loosen the carb connections and rip the rubber boot out and up between the frame rails and pull the carb up and through the same way with the cables still attached. I plug the intake manifold with paper towel and brush the loose dirt off the carb dirt with an old paint brush, throw an old bath towel under everything.

Easy to open the carb and service it now. But is there an easier way?
bill
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The faster it goes the faster it breaks.
And high performance=high maintenance.
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Old 05-29-2009, 05:43 AM   #80
laramie LC4 OP
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if you do that, you have to be careful not to fuck up the cables for the choke. be careful and i suppose this is an easy, quick way to access the carb. i wouldnt try and do any major work like this though, only emergency trail side stuff....

my $.02,

laramie
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Old 05-29-2009, 02:19 PM   #81
stephano
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Quote:
Originally Posted by bmwktmbill
Yes the blow job works well on any motorcycle.
I'll never look at my carb the same again.
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Old 05-31-2009, 09:25 AM   #82
Super Spook
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Hi guys,

New guy here. I have a 2001 Duke II that sat for over a year. Since it had constant throttle fueling issues when I put it away and had sat full of gas for so long, I figured now would be a good time to pull the carb apart to clean and start messing with jetting and such. I ordered some jets, a new airbox boot to replace the disintegrating one on the bike, and dug in using the info in this thread (very helpful BTW). Aside from the incredible pain in the ass that removing and reinstalling the carb is on these bikes, it all went pretty well. With one exception. Being the unfortunate combination of noob and dumbass that I am, I tossed the float weight in the containter of carb cleaner to soak with the rest of the jets.



The results were predictable. The little rubber conical tip kind of melted and deformed. I figured I'd put it all back in the bike anyway to see how it acted. Bike started right up with the new battery that I bought, and idled and revved great. Then started pissing gas out of the float overflow. So it looks like I need a new float weight. But I don't feel like paying $50 for the entire needle valve assembly. Does anyone have a source where the float weight can be purchased separately? Once I get one, I'll recheck my float level too, to make sure that isn't contributing to the problem. Any help would be greatly appreciated. Thanks guys.
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Old 05-31-2009, 01:43 PM   #83
Mike Figielski
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Working on jetting a '97 620 RXC with the stock BST40 carb. Waiting on main jets but today I drilled the slide holes to .125, set the needle clip to the 4th position from the top and adjusted the fuel/air screw to 2.5 turns out. Bike did not need much choke and the idle was too low. Adjusted the idle screw to compensate, I am assuming that is the correct thing to do.
The bike seemed more responsive and wheelied in 1st easier than before and pretty easily in 2nd which was more of an effort before the changes. Seems to be hunting (surging) a little at steady throttle at lower revs, not sure what that is - any ideas?
The fuel/air screw was at 2 turns and I went to 2.5. Does that make a drastic difference? I am assuming that is what effected the idle. It is hard to tell if the needle is better in the 4th position because the 142.5 main is definitely too lean. Ordering 150 thru 160 mains tomorrow so we'll see. Have the airbox modded and the stock Supertrapp that has been cored and has 8 discs. Any feedback would be greatly appreciated. thanks,
Mike
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Old 05-31-2009, 07:43 PM   #84
thaiseli
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One last question

So everthing seems to be going great, almost. Bike starts and runs with no gas leak, however I still get idling problems...not all the time but about half the time the bike dies in idle. It also seems not as peppy as it used to. The bike also starts easier when the choke is off, which seems odd to me. I'm 100 percent sure all the parts are in order. The only thing that isn't where it used to be is there was a washer on top of the throttle valve spring that popped out and I couldn't get back in. The washer seemed to compress the spring more and from looking at your bible you clip your spring so I figured I accomplished the same on accident. Any suggestions on getting it not to die in idle?
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Old 05-31-2009, 11:07 PM   #85
bmwktmbill
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Quote:
Originally Posted by thaiseli
So everthing seems to be going great, almost. Bike starts and runs with no gas leak, however I still get idling problems...not all the time but about half the time the bike dies in idle. It also seems not as peppy as it used to. The bike also starts easier when the choke is off, which seems odd to me. I'm 100 percent sure all the parts are in order. The only thing that isn't where it used to be is there was a washer on top of the throttle valve spring that popped out and I couldn't get back in. The washer seemed to compress the spring more and from looking at your bible you clip your spring so I figured I accomplished the same on accident. Any suggestions on getting it not to die in idle?
The important parts order is at the jet needle, washer and clip arrangement so that the needle hangs at the right length, also please double check that you tightened the rubber boot that holds the carb to the engine. Adjust the idle speed screw so that the engine idles at 1500 rpm, now adjust the idle fuel screw for fastest idle(around 2.5 turns open), now reset the idle to 1500 rpm. Ride.

If this doesn't work check the valves.
Stock jets should run perfectly at idle and through the range with the needle in the 4th position from the top.
b
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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 06-01-2009, 03:55 AM   #86
laramie LC4 OP
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Quote:
Does anyone have a source where the float weight can be purchased separately?
sorry. not that i know of but you may try some the larger carb suply shops like sudco or carbparts.com

what kind of solvent where you using to clean?

good luck,

laramie
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Old 06-01-2009, 02:18 PM   #87
Sparrowhawk
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Quote:
Originally Posted by laramie LC4
what kind of solvent where you using to clean?
Most of the bucket dip type carburetor and parts cleaners contain combinations of methylen chloride, cresols, xylenes, and ethyl benzene. Almost any type of rubber or plastic used in a carb will be weakened or destroyed by at least one of these ingredients. If you make the mistake of dipping a float bowl, rubber tipped float needle, o-ring, or gasket in this stuff you are probably best off going for a replacement part. After the swelling goes down, the part may look OK but it won't last long.

There are two ways to avoid the probem. 1) Be real careful not to dip your rubber tipped parts in places where it could get injured , or 2) move to California where the helpful bureaucrats ensure the carb dips you can buy are harmless to you, your rubbers, and mother earth.
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Old 06-02-2009, 06:29 AM   #88
meat popsicle
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Quote:
Originally Posted by Sparrowhawk
... or 2) move to California where the helpful bureaucrats ensure the carb dips you can buy are harmless to you, your rubbers, and mother earth.
trying to control the population here bub...
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Old 06-06-2009, 11:44 AM   #89
Mike Figielski
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Quote:
Originally Posted by Mike Figielski
Working on jetting a '97 620 RXC with the stock BST40 carb. Waiting on main jets but today I drilled the slide holes to .125, set the needle clip to the 4th position from the top and adjusted the fuel/air screw to 2.5 turns out. Bike did not need much choke and the idle was too low. Adjusted the idle screw to compensate, I am assuming that is the correct thing to do.
The bike seemed more responsive and wheelied in 1st easier than before and pretty easily in 2nd which was more of an effort before the changes. Seems to be hunting (surging) a little at steady throttle at lower revs, not sure what that is - any ideas?
The fuel/air screw was at 2 turns and I went to 2.5. Does that make a drastic difference? I am assuming that is what effected the idle. It is hard to tell if the needle is better in the 4th position because the 142.5 main is definitely too lean. Ordering 150 thru 160 mains tomorrow so we'll see. Have the airbox modded and the stock Supertrapp that has been cored and has 8 discs. Any feedback would be greatly appreciated. thanks,
Mike
Got my main jets and tried the 155 first. Definite improvement there. Also checked my needle and realized that the plastic spacer was not snapped right up against the clip so fixed that. Next went to a 157.5 main and put spacers under the stock airbox lid and adjusted the fuel/air screw to 2.5 turns out. Idle was better and popping on decel is almost gone. With 16/40 gearing it wheelies instantly in 1st gear and easily in 2nd gear. 3rd gear takes a lot of effort but the bike rips now. May try the 160 main but want to get it in the woods first. If I can find a needle shim I may try the clip at 3 1/2 instead of 4. Thanks to everyone who gave feedback and all of the long time members who contributed to the index and thanks to Laramie for creating the BST bible!. I ended up at almost the exact same set up as many others with similar mods have. great to have the combined knowledge and experience of so many riders. THANKS!
Mike
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Old 06-15-2009, 11:12 AM   #90
666
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So, where do I get replacement needle? Stock is the only option we have?

If I go to high elevation (WMRS) should I go back to 3 clip position? I run 4th at sea level.
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