lc4 enduro bogging after jumps?

[dagwood]

Originally Posted by creeper

Akcholee... I'd like to screw around with a Mikuni TMR41 (the one with the TPS they used on last years Huskyvarnishes) just for fun.

Husky couldn't get 'em to work, Husky owners couldn't get 'em to work... which makes 'em perfect for a pokity poker to pokity poke at.

Any '04 Husky owners that bought FCRs wana' donate their POS Mikuni TMR?

I've heard nothing but good things about the TMR. it's the squirt time and nozzle people had trouble with.. Way to long and fat and it would bog badly. TPS could go away too for that matter unless it' an 04 and up bike that might need it but it's easy enough to disable I hear. two screws and a wire?
at just over half the price of an FCR41
when you get one send me your bst slide. mine is still sticking :bludda

Yes I'm that tight. I'll take cheap and used anyday

[creeper]

Originally Posted by dagwood

I've heard nothing but good things about the TMR. it's the squirt time and nozzle people had trouble with.. Way to long and fat and it would bog badly. TPS could go away too for that matter unless it' an 04 and up bike that might need it but it's easy enough to disable I hear. two screws and a wire?
at just over half the price of an FCR41
when you get one send me your bst slide. mine is still sticking :bludda

Yes I'm that tight. I'll take cheap and used anyday

As soon as someone gives me a TMR... and I have it working well... you can "borrow" my slide.

How is it that your slide is sticking and you can't fix it?

[dagwood]

Originally Posted by creeper

As soon as someone gives me a TMR... and I have it working well... you can "borrow" my slide.

How is it that your slide is sticking and you can't fix it?

gummed up. poor maintenence, wore groves in the slide. only sticks when cold out or I need it to move right now. other than that it works fine.
just off idle sticks on the bottom end when it's cold out. tried everything else so I'm still thinking sticking slide. 11k of daily grime does that I guess. wish I would have moved the vent line sooner . Du'h.
whats a new slid anyway $35.00?
something else to add to the list.
If you sell my compessor I can get my "List" taken care of

[Esteban]

Originally Posted by ChrisC

The owners of replacement FCR's are so much faster 'cause their wallets are so much lighter...

Actually Chris that is not exactly true. A BST and five C notes still weighs less than one Kehein FCR 41. Now if you're a rich SOB like me and got the special order solid 24 kt gold model FCR you really have a weight disadvantage. That suckers weighs 8 pounds but man does it look good all shiny and golden. : )

SG in CO - who does like his FCR even if it was real expensive.

[meat popsicle]

Originally Posted by creeper

Akcholee... I'd like to screw around with a Mikuni TMR41 (the one with the TPS they used on last years Huskyvarnishes) just for fun.

Husky couldn't get 'em to work, Husky owners couldn't get 'em to work... which makes 'em perfect for a pokity poker to pokity poke at.

Any '04 Husky owners that bought FCRs wana' donate their POS Mikuni TMR?

Don't have the TMR in my punchcard file... is it anything like the TMS38?

my files say that was an interestin carb, evolution of the TMX, with a new flatside throttle and the cutaway is replaced by an internal chamber and two metering orifices (). No pilot jet - now metered by the jet needle. And, add a special needle (kit includes 5 needles for tuning) and you can simply remove the main jet (). The needle supposedly mixes the air and fuel more consistently than the main jet...

that leaves one screw for adjustments - but it says its for small two-strokers

[ChrisC]

Originally Posted by Esteban

Actually Chris that is not exactly true. A BST and five C notes still weighs less than one Kehein FCR 41. Now if you're a rich SOB like me and got the special order solid 24 kt gold model FCR you really have a weight disadvantage. That suckers weighs 8 pounds but man does it look good all shiny and golden. : )

SG in CO - who does like his FCR even if it was real expensive.

Steve....I'm old, slow, and cheap. Perfect candidate for the BST.

[d0gWateR]

Preface: Lotsa words here, no pictures. I am mechanically inclined, and technical by nature. Have rebuilt many engines over the years, but I have NOT spent much time tinkering with bikes. I have rebuilt a CR250R from a box of parts and a shop manual, so I'm no retard, but that's like following a recipe - no real knowledge required, just attention to detail. I love my LC4 and I am keen to learn more.

I'm in the cult of the LC4.

My setup: 2003 LC4 adv, Have the BST, raised needle one position, one size MJ up from 152.5 to 157.5 snorkel in. Have 82dB factory SM silencer fitted, not opened up. Quiet, works well, no power wheelies in any gear but first.

I ride single track insane junk with my pals on their 2 strokes, CRFs and such. My bike BOGS in the whoops. It doesn't stall for half a minute, but as long as I'm in whoops or large bumps at speed, it's like I hit the kill switch.

After my last ride: jumping water bars as we climbed a coastal mountain trail, my bike seemed to shut off just for second after each jump. Now, I will add that once I got home I saw that the fork seals had brushed the dust down to the very bottom of the stroke of the forks. They were bottoming (stock springs, rebound +2 clicks).

Also, on some "babies-head-boulder" trail climbs that were threatening to snake bite a tube, I didn't really have power delivery problems - very dangerous, very steep. Only 2 of us even attempted it.

So it would seem it's the larger amplitude hits that cause the problems, not "repetitive small amplitude bumpies".

In these conditions, my current carb setup is not adequate. But would a pumper be the answer, or can a CV cut it?

I'm watching this thread to see if I have an adjustment to make, or a carb to replace. I had a Mikuni pumper on my DR350 and didn't have this problem. I know the boys with CV carbs on their thumpers have been habitual complainers about CV carbs and bumps. The cure has always been, "Get a pumper!" Based in fact? Dunno.

If this is just something related to a "T-Vent" or float level, I'll be happy as a pig in shit. If the guys that run a BST can tell me that rush a set of whoops like they think they're RC on his new Suzuki and have no response problems from their carb I'm feeling good about checking float level or other carb problems. Otherwise, level with me, for serious offroading, is a pumper required?

Also, what about the FCR-39 vs 41?

I'm still trying to prove the only dumb question is the one left unasked.

Good tip with the clear hose for determing float level! Thanks!


Cheers, and thanks for all the heaps of good info over the last year lads. Keep posting!

[cbob]

DISCLAIMER: I'm just armchair wrenchin here, so upfront I apologize if I give misinformation (here's your cue, Creeper). I've only had 2 CV carbs apart in the last 5 years and I'm doing this from memory and carb diagrams, so there might be some error but the basic theories still hold (I think).

So, let's think about why a CV carb might be a problem . . . .

A CV carb has 2 vacuum chambers or "areas at work" (ok, more than 2, but 2 for this discussion). There is the chamber above the slide, separated from the rest of the carb by a diaphram and the chamber on the intake side of the slide. Don't forget the spring pushing the slide (and needle) closed. All the time. The only way to open the slide, raise the needle and allow air and fuel to reach the motor is to suck it open. Thus, throttle position, slide vacuum and spring tension must all be in harmony. PFM they call it (figure it out, one of the words is "freakin").

1.) Cutting the spring raises the slide for a given vacuum, letting more air and fuel to reach the motor for the same throttle position. Cutting the spring does not change the air / fuel mixture whereas raising the needle does. Or does it? Cutting the spring changes the air velocity past the needle jet. Remember, the throttle isn't as open as it was before, so although the slide air / fuel mix is set right, we might still be rich because the throttle is not letting as much air through. Want to cut your spring without cutting your spring? Try tying a few coils together with dental floss. Keep in mind the diameter of the coil, so 3 coils tied might equal 2 coils cut.

2.) Raising the needle (putting circlip on a needle position closer to the main jet) richens the mix. I suspect BST carbs were designed with a perfect 14:1 ratio to keep the CARB people happy. That would be CA Air Research Board or some stupid acronym, but they are the people behind establishing federal standards in keeping our combustible air clean, eliminating 2-strokes and leaning our performance motors. Somewhere around 12:1 is where the power is, and people like James Dean and Factory Pro can get you pretty close with a few $3 parts (which they sell for $70 - including "engineering" fees). BTW, raising a stock needle one notch (richer) is a cheap man's Factory Pro Ti needle. So, at the tip (3/4 throttle), a stock needle at #4 is the same as a Factory Pro at #3. At the fat end (1/4 throttle), the stock needle is very similar to the Factory Pro. Using Sudco's 6DH2,3,&7 needles (recommended in other discussions) goes 4 - 5 positions richer throughout the range. This may or may not be smart. No one has provided feedback on these needles. I have an Excel spreadsheet comparing needles if anyone wants it - just PM me with your email address.

3.) Drilling the slide opens the passage between the diaphram chamber above the slide and the carb intake chamber. Drilling the slide does not change the position of the slide or change the mixture, but makes the slide respond faster to changes in throttle position. Ah, finally - the elusive THROTTLE RESPONSE! But what goes up, also goes down. With larger holes the slide responds to changes in gravity faster, so a whoop or a jump landing can generate enough G force to lower the slide and, through slide position, essentially "chop" the throttle at a most inopportune time. With significant throttle position we now create a huge intake vacuum at the needle jet. But what goes down also goes up: As the slide maxes out and returns back up, it overshoots it's normal position and dumps raw fuel down the throat of the motor. I'm guessing lots of it if there's enough to kill motor power for 15 - 30 sec (or anything past a second). For anyone familiar with system control theory, there can be several oscillations until the slide returns to it's normal position again. Ever ride a bike with zero oil in the forks? What we need is a CV shock absorber!

I've been thinking a one way valve on the slide holes or some sort of miniature White Brothers cartridge fork inside the slide would fix both the throttle response and whoop problem, but there are a few obstacles . . . . Anyone who can make a cartridge fork at 1/10th scale in their home garage for less than $20 bucks is non-existent. Well, maybe McGiver could do it . . .

So let's explore the pneumatic approach: A simple one way valve made with a thin flap from feeler gauge stock and fastened with a screw would have to reside on the bottom, or intake side of the slide. I don't know about you, but screws or a broken flap in the intake passage scare me. We, collectively like the Borg, could make some sort of spring loaded ball (ball bearing?) drilled from the top side of the slide. Air pushing down bypasses the ball. Air pushing up seals the ball against a seat. The passage with the ball could be huge to allow large amounts of air through for increases in throttle position. With decreased throttle position, the slide can return normally. With whoops and jump landings the oscillations would be cut in half resulting in a more stable slide.

Anyone want to volunteer as a BST guinea pig? I might try the ball valve if somebody wants to donate a trashed (ie holes overdrilled) slide. I will admit, however, my tuning skills are maximized if the motor runs at all.

As a side note, my LC4-E did not die on whoops and hard landings (suspension severely bottomed out) while playing on an mx track, but everything was stock with needle at #3. I've not had a chance to really work with the carb, other than raising the needle to #4, and I'm still searching for that elusive throttle response. This week I'll be raising the stock needle to #5 and see what that does (along with a fatter main, prob 157.5). The biggest obstacle is I'd rather be on the 200!

Hopefully this discussion will generate some insight and more discussion in how a BST really works, it's limitations, how to maximize it and maybe try some new things.

Best,
- c bob

[meat popsicle]

Originally Posted by d0gWateR

If this is just something related to a "T-Vent" or float level, I'll be happy as a pig in shit. If the guys that run a BST can tell me that rush a set of whoops like they think they're RC on his new Suzuki and have no response problems from their carb I'm feeling good about checking float level or other carb problems. Otherwise, level with me, for serious offroading, is a pumper required?

I can shoot my keyboard off on a few of these things, but carb theory is not one of my knowledge bases. carb fellas, why is it that the CV carbs are more sensitive to big whoops?

Originally Posted by d0gWateR

Also, what about the FCR-39 vs 41?

They say the 39 gives more low end and the 41 more top end. lots of discussion hidden here and there. Ask flanny about that one for more info. Also ask him about the Mikuni TM-40 and pumper at half the price of the FCR...

[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.

[ChrisC]

Originally Posted by meat popsicle

I can shoot my keyboard off on a few of these things, but carb theory is not one of my knowledge bases. carb fellas, why is it that the CV carbs are more sensitive to big whoops?

"Slide bounce"....it's an inertia thing since the mass of the slide isn't hooked to anything (except unterdruck...)

[meat popsicle]

Originally Posted by ChrisC

"Slide bounce"....it's an inertia thing since the mass of the slide isn't hooked to anything (except unterdruck...)

so the pumper has a return spring to keep the slide more stable?

[ChrisC]

Originally Posted by meat popsicle

so the pumper has a return spring to keep the slide more stable?

The CV has a vacuum responsive slide with a throttle plate tie to the throttle cable.

The FCR style carb has the flat slide tied directly to the throttle cable.

So, the CV slide is at the mercy of airflow beneath it and the up and down motion of the whole bike. The flat slide carb throttle stays precisely where your left wrist places it....

[gybeman]

Originally Posted by meat popsicle

so the pumper has a return spring to keep the slide more stable?

In the pumper the slide is directly connected to your right wrist via the throttle cable.

[cbob]

Originally Posted by j0ney3

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.

We thought you would volunteer as our tester . . . .

Seriously, take your needle out, take it to the hardware store and pick up 2 or 3 extra circlips. See if the slide is drilled - 2 holes either side of needle, some people drill them to 1/8", easily measured with drill bits (originals are metric). I don't know what stock is. Do NOT drill the slide. 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.

Report back to the group.

Best,
- c bob