ADVrider

Go Back   ADVrider > Bikes > Thumpers
User Name
Password
Register Inmates Photos Site Rules Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
Old 02-17-2005, 05:49 AM   #1
j0ney3 OP
Gnarly Adventurer
 
j0ney3's Avatar
 
Joined: Feb 2004
Location: South Fl0rida
Oddometer: 315
lc4 enduro bogging after jumps?

Hey, I just got a 2001 lc4 enduro w/ 1000 miles on it. Stock everything, I think. Anyway, whenever I hit a jump, large bump, or some whoopdies, my bike bogs down like it's gonna die, sometimes it does die. If it doesn't die, it takes about 30 seconds of throttle fussing to bring it back to normal(throttle fussing=not riding, just keepin the bike running). The only thing I could think of was maybe the PO chopped those springs inside the carb, but I haven't taken that thing apart yet. Any ideas?
j0ney3 is offline   Reply With Quote
Old 02-17-2005, 06:29 AM   #2
cjflyfisher
cjflyfisher
 
Joined: Jun 2004
Location: colorado springs CO
Oddometer: 414
Sounds like all the fuel is leaving the bowl on a jump. I'd pull the bowl off and see if everything looks normal first. Maybe your missing a splash gaurd or similar gadget.

Need 640 carb specialist to chime in here
cjflyfisher is offline   Reply With Quote
Old 02-17-2005, 06:57 AM   #3
j0ney3 OP
Gnarly Adventurer
 
j0ney3's Avatar
 
Joined: Feb 2004
Location: South Fl0rida
Oddometer: 315
hrm, wouldn't know what I was looking for...paging Dr. Creeper...
j0ney3 is offline   Reply With Quote
Old 02-17-2005, 07:01 AM   #4
ChrisC
Molon Labe
 
ChrisC's Avatar
 
Joined: Feb 2003
Location: Prescott, Arizona USA Earth
Oddometer: 6,302
Quote:
Originally Posted by j0ney3
hrm, wouldn't know what I was looking for...paging Dr. Creeper...
Creep's still in bed...

This sounds like more than the dreaded BST "slide bounce", that is unless the previous owner really overdid the spring trimming.

Does the bike ever manifest the bad behaviour at other times, or is it a whoop/jump deal exclusively?

CC
__________________
Chris
'03 KTM Adventure 640
'43 BSA M20WD
ChrisC is offline   Reply With Quote
Old 02-17-2005, 07:04 AM   #5
j0ney3 OP
Gnarly Adventurer
 
j0ney3's Avatar
 
Joined: Feb 2004
Location: South Fl0rida
Oddometer: 315
Well, it doesn't really like to be bogged down in heavy sand, but it clears out as soon as i can get the revs up. But, no , it only happens on big whoops and jumps.
j0ney3 is offline   Reply With Quote
Old 02-17-2005, 07:08 AM   #6
ChrisC
Molon Labe
 
ChrisC's Avatar
 
Joined: Feb 2003
Location: Prescott, Arizona USA Earth
Oddometer: 6,302
Quote:
Originally Posted by j0ney3
Well, it doesn't really like to be bogged down in heavy sand, but it clears out as soon as i can get the revs up. But, no , it only happens on big whoops and jumps.
It shouldn't load up in that situation either. Maybe a good first step would be to take the 17 mm plug out of the bottom of the float bowl. Then pull the main jet (don't lose the little brass collar that surrounds it). The OEM jet was a 142.5. If it's bigger, that'll be a hint if the carb has been diddled with, and you can also check for contamination of the fuel...

CC
__________________
Chris
'03 KTM Adventure 640
'43 BSA M20WD
ChrisC is offline   Reply With Quote
Old 02-17-2005, 07:11 AM   #7
ChrisC
Molon Labe
 
ChrisC's Avatar
 
Joined: Feb 2003
Location: Prescott, Arizona USA Earth
Oddometer: 6,302
Oh....and as an aside, when it's "bogged out", if you pull the enrichening (choke) lever does it get better or worse?

If it gets better you're likely looking at a restriction in fuel flow.

If it gets worse then it's too fat....maybe a float issue?
__________________
Chris
'03 KTM Adventure 640
'43 BSA M20WD
ChrisC is offline   Reply With Quote
Old 02-17-2005, 07:13 AM   #8
j0ney3 OP
Gnarly Adventurer
 
j0ney3's Avatar
 
Joined: Feb 2004
Location: South Fl0rida
Oddometer: 315
sweet, i'll check tomorrow...is there anywhere i can find some pics of this BST thing that everyone keeps talking about?

awesome, i'll try that choke manuver this weekend. This whole "carb" thing is messin me up(just sold my r11gs)
j0ney3 is offline   Reply With Quote
Old 02-17-2005, 07:21 AM   #9
ChrisC
Molon Labe
 
ChrisC's Avatar
 
Joined: Feb 2003
Location: Prescott, Arizona USA Earth
Oddometer: 6,302
Try this:

BST parts

It's from H&H's (Georgia) parts department (online). Really helpful site...check it out

CC

p.s. you can now consider yourself a noviciate in the Cult of the BST...
__________________
Chris
'03 KTM Adventure 640
'43 BSA M20WD
ChrisC is offline   Reply With Quote
Old 02-17-2005, 07:31 AM   #10
cbob
Gnarly Adventurer
 
cbob's Avatar
 
Joined: Oct 2004
Location: Buford, GA
Oddometer: 205
Check the needle clip position. Stock is middle, some recommend moving to 4th from top (richer). If you move it one more position you emulate the Factory Pro needle. This should not be a problem with whoops and jumps.


Check to see if the slide has been drilled. I don't know original size holes, but the recommendation is to drill them to 1/8". This would cause the slide to respond faster to change, like sudden weight changes (G outs) to the slide. Flanny cautioned that drilling the slide can cause bogging in whoops and jump landings. Your condition sounds severe if it takes 30 sec to clear out. If the slide is drilled you can epoxy one hole and drill a small hole next to it. Remember, the other hole is still 1/8" so you need a total area equal to the original holes (which I don't have size info for).

There is no dampening with the carb slide, so the carb could be flooding after the slide spring rebounds (tops out after bottoming out). With a weaker spring (2 or 4 coils being clipped) it would not push down on the slide as much.

Like Chris C says, float bowl should probably be checked.

Let us know what you find, for the sake of the BST cult following.

- c
__________________
Dream House Family Fun Ride - May 3, 2009
Dream House 500 Adventure Ride - October 3, 2009

to benefit the Dream House for Medically Fragile Children
www.dreamhouseforkids.org
cbob is offline   Reply With Quote
Old 02-17-2005, 12:40 PM   #11
neduro
Addict
 
neduro's Avatar
 
Joined: Jul 2003
Location: Colorado Springs, CO
Oddometer: 11,703
I am not an expert with that particular carb, but have had a similar experience from two different causes:

1) Float height too high, or lower limit to float travel too low. If there's too much fuel in the bowl, and then the force of the landing pulls the floats down and lets more in, that can explain it- lower the float height. Also, on XR carbs, you can limit how far down the floats are able to travel- if they can go all the way to the bottom of the bowl, you can get bad carburation even with proper float height.

2) Insufficient carb venting- try putting a "T" in on the breathers, as close to the carb as practical, and running the new line straight up to under the tank. If the breather is filled with fuel, the bowl can't breath and you'll get a weird vacuum situation. Can't explain the physics but can tell you it matters to get it right.
__________________
Doubletake Mirrors- Folding D/S mirror that is both useful and indestructible.

Dual Sport Riding Techniques DVDs: Clear instructional DVDs to improve off-road skills.
neduro is offline   Reply With Quote
Old 02-17-2005, 01:16 PM   #12
creeper
Still alive...
 
creeper's Avatar
 
Joined: Dec 2003
Location: Puget Sound
Oddometer: 10,718
Quote:
Originally Posted by j0ney3
sweet, i'll check tomorrow...is there anywhere i can find some pics of this BST thing that everyone keeps talking about?

awesome, i'll try that choke manuver this weekend. This whole "carb" thing is messin me up(just sold my r11gs)
Before any armchair (computer desk) diagnostics, it would be good to know what you have for jetting and modifications if any.

For some unknown reason, I have yet to measure the free length of a vacuum piston spring, so I don't have a reference for you there. You can look to see if it has been unceremoniously snipped however, as opposed to a clean machine made end.

Next is jetting and needle clip position, followed by measuring the size of the transfer ports in the slide, found on either side of the hole the needle goes thru.
While your there, check:
The order of the various washers and spacers on the needle, when compared to an exploded drawing.
The condition of the vacuum diaphragm. Holes, pinch marks and the like.

The vents previously mentioned by my fellow armchair carb experts, and the vent under the diaphragm as well (see item circled)



Has the snorkle atop the airbox been removed?
Is there a high flow side cover?
Does fuel flow well from the petcock?

And last but not least, I was given a spec for a float level wet test of 0 to 2mm below the center of the float bowl gasket surface at the center of the float bowl.
I have not tested this to compare it to a known correct float level... so it could an inaccurate figure.

How to perform a "wet test" you ask
Replace the black bowl drain hose with a clear one and tape it to the carburetor so that it is centered on the bowl at the bowl / carb body gasket surface.
Level your bike, open the drain screw (see item circled) You should see your bowl fuel level in the hose. You can also start your bike and watch the "running" fuel level.

Thats all fer' now
Chris
__________________
So... how's tricks?
creeper is offline   Reply With Quote
Old 02-17-2005, 01:56 PM   #13
ChrisC
Molon Labe
 
ChrisC's Avatar
 
Joined: Feb 2003
Location: Prescott, Arizona USA Earth
Oddometer: 6,302
Quote:
Originally Posted by creeper

The vents previously mentioned by my fellow armchair carb experts, and the vent under the diaphragm as well (see item circled)


Has the snorkle atop the airbox been removed?
Is there a high flow side cover?
Does fuel flow well from the petcock?


Thats all fer' now
Chris
'Bout time you got out of bed. And why do you have a Pet Cock?
__________________
Chris
'03 KTM Adventure 640
'43 BSA M20WD
ChrisC is offline   Reply With Quote
Old 02-17-2005, 02:41 PM   #14
creeper
Still alive...
 
creeper's Avatar
 
Joined: Dec 2003
Location: Puget Sound
Oddometer: 10,718
Quote:
Originally Posted by ChrisC
And why do you have a Pet Cock?
That all you got? Man, you is slippin' down the long hill to...
__________________
So... how's tricks?
creeper is offline   Reply With Quote
Old 02-17-2005, 06:26 PM   #15
j0ney3 OP
Gnarly Adventurer
 
j0ney3's Avatar
 
Joined: Feb 2004
Location: South Fl0rida
Oddometer: 315
Quote:
Originally Posted by creeper

Has the snorkle atop the airbox been removed?
Is there a high flow side cover?
Does fuel flow well from the petcock?
yes.
no.
I don't know what flowing well should be.

BST cult, holy shit, is there anyone who rides an LC4 who is even remotely sane? Is the LC4 the culprit of said insanity, is the BST? I guess I'll rip apart the BST this weekend and take some pics...what have I done?
j0ney3 is offline   Reply With Quote
Reply

Share

Thread Tools Search this Thread
Search this Thread:

.
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


Times are GMT -7.   It's 09:55 AM.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2014