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Old 11-08-2012, 09:17 AM   #1156
motolab
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Quote:
Originally Posted by SuperPivis View Post
Hi thanks again for answer. I've been playing with the bike yesterday , put it back to 2.5 turns and had the test ride and it pulls well.
The pilot screw should only be used to tune the idle mixture. Anything that is not idle is the responsibility of other components. Correspondences on CV carbs:

Low rpm all throttle positions: float height, needle base diameter, emulsion tube outlet size
WOT operation overall: main jet
WOT operation between HP peak and red line: main air corrector
WOT operation below red line: jet needle shape
1/4 throttle opening: jet needle clip position
1/8 throttle opening: pilot jet size
1/16 throttle opening: pilot jet size
idle: mixture screw adjustment
Quote:
Did not try stock settings (2.25) because I think it would be too lean. I know u said that I should not go by the color of spark plug ,, but even the spark plug is getting to right color, it's not white anymore..So I think it is adjusted good now..
Again, procedure for adjusting the idle mixture:

Lower the idle speed a little bit (this increases the sensitivity, so you can more easily notice the effects of your adjustment). Adjust the fuel screw in until you notice it is running worse, then adjust out to the point where the idle is the strongest, and then no more than 1/8-1/4 turn further. Adjust the idle speed back to normal.

Regards,

Derek
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Old 11-08-2012, 10:18 AM   #1157
SuperPivis
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Hi ,,
I've been adjusting it as you saying all the time ,, but I would say that idle was strongest on 2.25 to 2.50 . so I left it on 2.50
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Old 11-29-2012, 07:52 AM   #1158
air0n
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Great post! Hopefully someone can enlighten me. I picked up a bike that is not running. When I broke down the carb, three of the four idle jets had a plug. I have searched the web heavily and have yet to find any info about this plug. In fact, any pics I see of these carbs do not have the plug. Is this required?



Thanks in advance!
Aaron
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Old 11-29-2012, 09:35 AM   #1159
motolab
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Quote:
Originally Posted by air0n View Post
Great post! Hopefully someone can enlighten me. I picked up a bike that is not running. When I broke down the carb, three of the four idle jets had a plug. I have searched the web heavily and have yet to find any info about this plug. In fact, any pics I see of these carbs do not have the plug. Is this required?



Thanks in advance!
Aaron
Hello Aaron,

The carburetor pictured is not a BST40.

Regards,

Derek
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Old 11-29-2012, 12:13 PM   #1160
air0n
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Quote:
Originally Posted by motolab View Post
Hello Aaron,

The carburetor pictured is not a BST40.

Regards,

Derek
haha That would explain a lot! I will keep digging. Thanks for the reply!

Aaron
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Old 12-04-2012, 12:14 PM   #1161
xam
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Hey Friends,

i just bought a LC4 640 Sixdays with 4.440km in an excellent state.

I'm very happy with it, and there is nothing i would like to change if i don't have to.
Then last Sunday i went out with a friend to ride some enduro and we passed a few ditches, knolls and stuff like that.
Shortly after the KTM came back in a straight position, the engine idle got very slow and it died completely.
The starter took a while to get it back to life.

I think it has to be a carb problem, i heard the BST-40 should be not a good choice at difficult offroad sections und deeper bumbs. Is there any chance to get this problem fixed, i don't want to buy a new carb, i don't have the money for this, too.

I hope you can help me with this problem.

cheers
Toby
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Old 12-04-2012, 02:21 PM   #1162
gunnerbuck
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Quote:
Originally Posted by xam View Post
Hey Friends,

i just bought a LC4 640 Sixdays with 4.440km in an excellent state.

I'm very happy with it, and there is nothing i would like to change if i don't have to.
Then last Sunday i went out with a friend to ride some enduro and we passed a few ditches, knolls and stuff like that.
Shortly after the KTM came back in a straight position, the engine idle got very slow and it died completely.
The starter took a while to get it back to life.

I think it has to be a carb problem, i heard the BST-40 should be not a good choice at difficult offroad sections und deeper bumbs. Is there any chance to get this problem fixed, i don't want to buy a new carb, i don't have the money for this, too.

I hope you can help me with this problem.

cheers
Toby
When the 640 dies in the bumps and whoops it usually means the fuel level in the float bowl is off... I would check your float height setting, the float needle and related float valve O-rings... If the bike is more than a few years old the float needle tip and the needle seat o-ring rubber may be decomposed and should be replaced as they will not properly shut the fuel flow off as the float rises....

- IF the float height is too far off from the ideal setting {too high or too low} the fuel in the float bowl when jostled by the bumps may do the following: If the fuel level is too high then too much fuel gets through the jets causing richness, engine flooding and stalling ... If the fuel level is too low then bumpy ground will cause not enough fuel into the jets and make the engine bog and cut out...
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Old 12-04-2012, 04:26 PM   #1163
bisbonian
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Quote:
Originally Posted by laramie LC4 View Post
-you should now have the slide support and needle jet sitting on your workspace.



-while you are looking at your slide support, check to make sure that their is an O-ring seated at the topside, if not it is still in the carb and needs to be pulled out. mine likes to stick so I usually end up fishing it out...


I just took my carb apart for a bit of a cleaning up and found that the o-ring mentioned here came out in pieces.

I'm pretty sure that's not right.

Anyway, should the local hardware store have a replacement?

What sort of issues could I expect to see with this o-ring torn in half (if any)?
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Old 12-05-2012, 12:57 AM   #1164
xam
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Quote:
Originally Posted by gunnerbuck View Post
When the 640 dies in the bumps and whoops it usually means the fuel level in the float bowl is off... I would check your float height setting, the float needle and related float valve O-rings... If the bike is more than a few years old the float needle tip and the needle seat o-ring rubber may be decomposed and should be replaced as they will not properly shut the fuel flow off as the float rises....

- IF the float height is too far off from the ideal setting {too high or too low} the fuel in the float bowl when jostled by the bumps may do the following: If the fuel level is too high then too much fuel gets through the jets causing richness, engine flooding and stalling ... If the fuel level is too low then bumpy ground will cause not enough fuel into the jets and make the engine bog and cut out...
I will check this, thanks!
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Old 12-06-2012, 11:56 AM   #1165
faustinoeldelbarrio
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I've been trying to carb properly my 640 adventure (2006) for quite a while, however during the last 3 months I couldnīt work much on it, and now that I got the time i am sensing it's not running quite well. I have read a fair amount on forums and other internet places to understand the principles of how a CV carb works but the roots of the misbehavior don't seem obvious.
At high rpm's the bike has good power and response at all throttle openings for what I have tested; however as the rpm's lower, the performance also goes down. The feel is as if something held the bike. The response is really slow and thereīs no much power there. When the rpm's reach about 5K then the beast becomes alive and pulls like a real 640. This problem at mid and low range is common to all throttle positions, the bike just feels like it only had 200 cc (am I being clear?). There is also a point around 4.5K rpms when at WOT the bike loses all power for a second or two and then gets the boost again.
The lack of power at medium and low range is really annoying since there's where I like to stay when riding off road or in traffic jams.
The setup of my bike is :

Pilot jet: 47.5
Main Jet: 157.5
Needle clip in the second notch (counting from the top)
Drilled slide (considering to buy a new one and leaving it alone)
Snorkel Removed
Full Akra system (with DB killer )

The bike has around 17k kms (around 11k miles)
I ride at 2600 m (around 8600 ft)

the air filter was cleaned and oiled about 2 months ago so that shouldn't be the problem.

Thanks in advance !
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Old 12-06-2012, 01:15 PM   #1166
motolab
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Quote:
Originally Posted by faustinoeldelbarrio View Post
At high rpm's the bike has good power and response at all throttle openings for what I have tested; however as the rpm's lower, the performance also goes down. The feel is as if something held the bike. The response is really slow and thereīs no much power there. When the rpm's reach about 5K then the beast becomes alive and pulls like a real 640. This problem at mid and low range is common to all throttle positions, the bike just feels like it only had 200 cc (am I being clear?).
Does the problem get worse or improve as the engine warms up? How about when the cold start enrichment circuit is active vs. when not?

Regards,

Derek
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Old 12-06-2012, 07:19 PM   #1167
bmwktmbill
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You could rejet and clip it to OEM settings and run it for a proper personlal baseline since like most of us you don't have a dyno.
At least you would know one thing for sure.

Have you set the valves and tightened the carb to the engine?

Have you tried a run without the air cleaner in place?

Is the needle stock?

Is the cam stock?
bill
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The faster it goes the faster it breaks.
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Old 12-07-2012, 04:42 AM   #1168
laramie LC4 OP
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Quote:
Originally Posted by bisbonian View Post
I just took my carb apart for a bit of a cleaning up and found that the o-ring mentioned here came out in pieces.

I'm pretty sure that's not right.

Anyway, should the local hardware store have a replacement?

What sort of issues could I expect to see with this o-ring torn in half (if any)?
i used one out of a fuel resistant o-ring kit that i had. worked fine. just find one that is the right size. should be pretty cheap >$1.

laramie
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Old 12-07-2012, 09:20 AM   #1169
faustinoeldelbarrio
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Quote:
Originally Posted by motolab View Post
Does the problem get worse or improve as the engine warms up? How about when the cold start enrichment circuit is active vs. when not?

Regards,

Derek

Hi Derek,

The problem seems to get worse when the engine warms up, specially at that point when the bike starts moving while one releases the clutch (very common situation in traffic jams) which points out a rich mixture, however this change is not very noticeable with the change in temperature.
When starting up the bike the enrichment circuit helps. Once the bike is warm the enrichment circuit does nothing but mess more the performance.
As for the valves they havenīt been set, and i run an original cam.
The carb is properly tightened to the boots.
Today I took the db killer out and found that it was covered in black powder (don't really know the term in English for That CO2 accumulation).
The only things that occur to me right now is that i have a worn emulsion tube, or an incorrect float height ( not really probable since about a year ago i changed the float valve and checked the height about 3 months ago and everything seemed to be in place).
I What other things can cause this problem?, and btw which is the standard main jet for lc4's with high flow heads?

Thanks
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Old 12-07-2012, 06:38 PM   #1170
gunnerbuck
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Quote:
Originally Posted by faustinoeldelbarrio View Post
Hi Derek,

The problem seems to get worse when the engine warms up, specially at that point when the bike starts moving while one releases the clutch (very common situation in traffic jams) which points out a rich mixture, however this change is not very noticeable with the change in temperature.
When starting up the bike the enrichment circuit helps. Once the bike is warm the enrichment circuit does nothing but mess more the performance.
As for the valves they havenīt been set, and i run an original cam.
The carb is properly tightened to the boots.
Today I took the db killer out and found that it was covered in black powder (don't really know the term in English for That CO2 accumulation).
The only things that occur to me right now is that i have a worn emulsion tube, or an incorrect float height ( not really probable since about a year ago i changed the float valve and checked the height about 3 months ago and everything seemed to be in place).
I What other things can cause this problem?, and btw which is the standard main jet for lc4's with high flow heads?

Thanks
The standard jets are:
main - 152.5
Pilot - 45
Needle - 3rd clip {middle}
Float - Parallel with gasket surface

In trying a 47.5 pilot on both of my 640s I found it too rich and ended up going back to the 45, this is at sea level... You may want to try a smaller pilot for your application...

A worn needle jet/emulsion tube will very much cause your bike to run like crap... A big noticeable performance increase comes with the replacement of the worn parts... You may want to check the wear indicators on the slide and slide guide to see if they are also worn...
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