lc4 enduro bogging after jumps?

[ChrisC]

Originally Posted by cbob

Move the circlip 1 position (your choice) then fling the bike over a jump, being sure to pancake it for style points . Now land . Does the engine dying get better? Does it get worse? If worse, remove the needle, move the clip 2 positions the other way (you did remember to bring the extra circlips with you, right?), and repeat.

Conventional wisdom says that the movement of the needle's circlip up or down can effect your mixture between 1/4 and 3/4 throttle (rich/lean). How it might somehow have a positive effect on the inertia closing of the vaccum operated slide during a high-G whoop is news to me...

[DirtyVFR]

Originally Posted by j0ney3

Not tryin to start shit but, can someone honestly say that I can fix these bogging problems with the BST(or any CV carb for that matter)? Or am I looking at -$ for a pumper? I'm not talkin about 75ft gap jumps, just barely catching air does it. Same w/ the whoopdies, these are not jeep swallowers, just small ones.

J0ney3,

I think your question has been answered. If you change to a pumper carb, it will fix the problem.

If you insist on keeping the CV carb, there are a bunch of twiddles to attempt. You could pioneer a solution. But if there was a definitive, guaranteed CV mod, everyone would have done it. It may be that the bone stock settings of your CV (including all the emissions equip) was as good an all round compromise as possible.

Originally Posted by meat popsicle

ps - I think flanny could answer this question the best as he set up his BST very well, then went to a TM-40, and I think he ended up with an FCR.

I saw enough people do this that I decided I just wanted to be DONE with the carb thing. The only arguments against the FCR is an attempt to save money. But if you include TIME into the equation, doing your carb multiple times is the most expensive option.

I also recognize there are people who have lots of time but very little cash budget for the bike. Also, some people actually like to fiddle with the bike more than ride it, or they don't have the opportunity to ride, so working on the bike is the next best thing.

So I think that's the whole formula. You need to decide where you are on the TIME-MONEY-RIDING-TWEAKING matrix and choose appropriately.

[creeper]

I really wanted to avoid this topic, rather just read the various posts and see where it goes.
But… I guess I can toss in a few cents worth by offering up what I know, or think I know.
If I’ve repeated something someone else has already said, or thought or may think of tomorrow… sorry.

CV slides don’t “bounce� around as much as you might think. I’ve observed the slides in operation on Kehien carbs, on Harleys, on the dyno.
At idle, they, for lack of a better term, “flutter� or pulse with the operation of the engine. They rise slightly during the intake stroke and lower slightly during the other remaining events.

When you open the throttle, the slide rises a split second behind the movement of the throttle plate, and if the throttle is held, stabilizes and goes into its fluttering act, but the up and down movements are shorter… the slide almost stationary.
When you chop the throttle, the slide lowers, not an instantaneous drop… or molasses slow, but rather in an immediate, yet damped fashion.

I’ve reached in and manipulated slides to see what effect it has and found that the pressures applied to them are not easily overcome. Several ounces of force are required to manually move a slide up or down. They are held in balance between negative and positive pressures.
When they are manipulated, and released, they return to their original position… immediately.
I have done this with both the stock alloy slides as used by Harley and with the Dynojet plastic slides as used in their performance carb hop-up kits.
If anything, the plastic slides are even more difficult to manipulate as they have less mass.

Air is a fluid, and as long as the engine is running, that fluid is moving thru the carburetor, creating the pressures previously mentioned and holding the slide in a balance.
Drilling holes in the slide alters that balance, clipping coils from a spring alters that balance.
Enlarging the transfer ports alters the slides response time, and that modification by itself may alter the mixture strength during transition from one throttle position to another. Under steady throttle it has no effect on mixture strength, as once the slide stabilizes to the throttle position it would be neither higher nor lower in the venturi.
Clipping spring coils has a similar effect, except that, in addition, assuming the springs tension has a bearing on the slides final location for a given throttle position, the slide will stabilize at a location higher in it’s bore, increasing the venturi opening.

What happens if we enlarging the transfer ports “too much�? I believe we are looking at a peaked line graph, and our shade tree rocket science 3mm drilled slides are on the leading surface, slightly below the peak. With a bit of experimentation, we could probably locate that exact peak and have near “FCR like� throttle response. In exchange we would loose some, if not all of the smooth response CV carbs are known for, and would in all likelihood need an accelerator pump to compensate for the temporary lean condition we will have created.

Based on what I’ve learned, I have a hard time believing that a slide will rise or fall dramatically due to the relatively minor effects of variable geography. I do believe however that a CV throttle can be manipulated quickly enough (on purpose or inadvertently) that the slide can be “in the wrong place at the wrong time�.

CV carbs are popular with manufacturers because they work well when jetted emissions lean and with only one “market driven� exception I am aware of, do not require an accelerator pump. Can they be made to perform as well as a slide carburetor? Sometimes close… but never “as well�.

FCR and similar carbs are popular with riders because they can, when set up properly, offer near instantaneous throttle response and in some cases more top end power due to the “cleaner� venturi throat. The fact that they require and accelerator pump to compensate for the temporary poor vacuum signal that occurs when the slide is whacked open, is no doubt of small consequence to legion of happy owners.

OK. That all said, I run a CV because I am a cheap bastard, an obstinate and contrary cheap bastard, I get a kick out of trying to turn a emissions carb into a semi-performance carb for next to nothing and… I am an old, obstinate, contrary and cheap bastard.

Would I buy and FCR? No. Only because it’s just too damn easy.

[dagwood]

jeez what a grump.

Hey Creeper I'm thinkin I can get a deal on a Weber. think we can get it to work? not one of them cheapass Holley webers but A real side draft 44.
space would be an issue but I can ditch the airbox and hang it out the side with a pair O'big velocity stacks.


























I'm tighter than you are creeper on top of being poor

[ChrisC]

Originally Posted by creeper

CV slides don’t “bounce� around as much as you might think.
Based on what I’ve learned, I have a hard time believing that a slide will rise or fall dramatically due to the relatively minor effects of variable geography. I do believe however that a CV throttle can be manipulated quickly enough (on purpose or inadvertently) that the slide can be “in the wrong place at the wrong time�....

So, all that being said, you don't attribute the alleged flat spot to slide inertia but rather to some obscure "wrong place/wrong time" analogy...?

Mind you, I've never experienced the complaint being both way too old and way too slow....not to mention waaaay too cheap to admit it

[creeper]

I know where there are a whole bunch of Amal monoblocks.

[ChrisC]

Originally Posted by creeper

I know where there are a whole bunch of Amal monoblocks.

Sorry, only the Concentric version will do...

[creeper]

Originally Posted by ChrisC

So, all that being said, you don't attribute the alleged flat spot to slide inertia but rather to some obscure "wrong place/wrong time" analogy...?

Yep PFM. Really, I've got a few hours in watching and poking at CV slides in operation, which is prolly a few hours more than anyone else 'round here. So, short of a "from the airbox" video of slide movement, or at least a sensor and oscilloscope rig... I ain't havin' it.

Go ride you bike in some dirt, and rapidly open and close your throttle while under a medium load... treat it like it was an FCR... no rolling, just snap that sucker open and close a few times under load.

See what happens? Air can transit from one direction to another quickly... fuel? not so much.

[DirtyVFR]

Originally Posted by creeper

CV slides don’t “bounce� around as much as you might think.
Based on what I’ve learned, I have a hard time believing that a slide will rise or fall dramatically due to the relatively minor effects of variable geography. I do believe however that a CV throttle can be manipulated quickly enough (on purpose or inadvertently) that the slide can be “in the wrong place at the wrong time�....

Creeper,

I can fully accept the mechanism explaining CV "Bounce" could be an Old Dirt Tale. But not the symptom itself. I was told it would happen, I experienced it happening, my mechanic reiterated "that's why it happened", and now the problem under discussion is the same.

So we KNOW it happens. The bike stutters or stalls off jumps.

Putting on a pumper carb fixed the problem for me and countless others. HOWEVER -

I could also accept "as the BST ages, deposits accumulate"...thus the "wrong place/wrong time effect" happens when you go off jumps... OR it's, "the springs get weak over time", or "small holes let air leak"... or whatever. It doesn't have to be "Slide inertia." Any "wrong place/wrong time" theory works as long as "thus the engine stalls when going over jumps" is the accepted outcome.

If I had been offered that a $100 rebuild would fix the problem for another 7,000 miles I probably would have gone for that. If a rebuild fixed the problem for only 1,000 miles, I'd still have picked the FCR.

But do we know of anyone who can take this symptom, mod the BST, and make it go away (even for a while)? I think that's what the poster is after.

(Plus, now I'm curious.)

[creeper]

Originally Posted by DirtyVFR

But do we know of anyone who can take this symptom, mod the BST, and make it go away (even for a while)? I think that's what the poster is after.

(Plus, now I'm curious.)

I'm sure the symptom you and others describe exists, but I have no first hand experience with it... riding under similar circumstances and terrain that you and others have described, it has never happened to me.

Maybe one of these days I will experience it, and with a little luck learn what the cause is. Until then, for those that it seems to affect, the guaranteed cure appears to be an FCR.

Creep

[meat popsicle]

Originally Posted by creeper

I'm sure the symptom you and others describe exists, but I have no first hand experience with it... riding under similar circumstances and terrain that you and others have described, it has never happened to me.

Maybe one of these days I will experience it, and with a little luck learn what the cause is. Until then, for those that it seems to affect, the guaranteed cure appears to be an FCR.

Creep

or a Mikuni TM at half the price

where's the flannimal? what's the up and downside of that pumper?

[dagwood]

Originally Posted by meat popsicle

or a Mikuni TM at half the price

where's the flannimal? what's the up and downside of that pumper?

adapting the cables ...other than that none. read his report on tuning it.
look up his site in orange crush. thats his playground now.

I see we're still at it here, eh? Creeper, when I was considering mods to my diaphram carb on my 640LC4, I briefly considered modifing the slide and cover to accept a cable to manipulate the slide directly, eliminating the vacuum dependant diaphram set-up. My experience with my bsts were that force would overcome vacuum and the engine would have to build it back up before the throttle would respond, sometimes stalling the engine or putting it into a rough idle for up to 30 seconds or so, similar to running out of fuel. This, I assumed would also eliminate the lag this carb seems to suffer from. My DellOrtos never suffered from bogging that I had read about from big singles without a fuel pumper carb, 620SX, 640D/S and Duke 11. Any thoughts. P.S., if this is the BST breakthrough of the century, we can skip our race bet, the coffee is on you my friend, if not, there is still a money back garantee on all free advise, LOL, Jim.

[meat popsicle]

Originally Posted by dagwood

adapting the cables ...other than that none. read his report on tuning it.
look up his site in orange crush. thats his playground now.

i have seen the guide and read his posts where he reconsiders the whole pursuit of power with the LC4 Adv. as u recollect it sounds like the bike might loose it's manners. sure the Rallye uses the FCR but its setup for desert screaming right? not my ball game. I would rather use the 3-500 bucks on other things.

i know when i my bike is cold and i hit the brakes hard enough to make the front dive deep it will stall - but it never happens when its warm. and i am bottoming out the front forks to trigger the traffic light pads (damn them - setup for cars...). sure I look like an idiot but I FEEL like an idiot when I wait a few light cycles until a car pulls up behind me and triggers the pad... so I can't imagine that anything I could do in the dirt would be "rougher" on the slide action or whatever those gurus are discussing than that.

[dagwood]

Originally Posted by meat popsicle

i have seen the guide and read his posts where he reconsiders the whole pursuit of power with the LC4 Adv. as u recollect it sounds like the bike might loose it's manners. sure the Rallye uses the FCR but its setup for desert screaming right? not my ball game. I would rather use the 3-500 bucks on other things.

i know when i my bike is cold and i hit the brakes hard enough to make the front dive deep it will stall - but it never happens when its warm. and i am bottoming out the front forks to trigger the traffic light pads (damn them - setup for cars...). sure I look like an idiot but I FEEL like an idiot when I wait a few light cycles until a car pulls up behind me and triggers the pad... so I can't imagine that anything I could do in the dirt would be "rougher" on the slide action or whatever those gurus are discussing than that.

That the impression I got too. to much to soon and your at the limit of traction anyway. it's not like we can run Paddle tires. Controled response not an off/on switch...works for me..
ps I've pancaked hard enough to wrack my nuts and turn my eyes yellow and my bike didn' stall or spudder. I did but thats a normal response to getting kicked in the nuts.