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Discussion Starter #1
Just wondering whether it would be wiser for me to do the 22 Cent Mod or go the KLX Needle and new jets route. Currently my 2017 is surging (slightly but noticably) while cruising, and popping through the exhaust (again, slightly) when engine braking from cruising RPMs. I basically just want it to work right, but of course a bit more power would be welcome. The .22 mod seems like a good choice, well tested etc., and has the bonus quality of using mostly stock parts. Also, I'm concerned that if I start messing with the jets, it will be lot more trial and error << this wouldn't be all bad, but I'm curious to hear from the group: Are there any advantages to putting in the new needle and jet, if I'm sticking with stock exhaust? If I start re-jetting, am I going to also want to do the L mod, again, considering the stock exhaust?
 

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Both are tried and true, both work, but the KLX is the way to go. The 22 cent mod will richen things just a tad, enough to get rid of the lean surge. The needle is the same, though, with the stupid-rich full throttle. The KLX has a completely different taper and richens things up more properly. It also has tunability into the future if you decide to mod things up a bit.

There is no experimenting required, either. It's like making Tollhouse cookies with the recipe on the bag. Buy the kit, follow the directions for what you have on your bike and it will work.

It's $50 vs 22 cents, but most people think it worthwhile.

You can do it to a completely stock bike. It will give you a more responsive throttle, The bike will be peppier with more vim, vigor, and vitality, but don't expect to do roll-on wheelies. KLRs don't do roll-on wheelies.
 

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Discussion Starter #3
Awesome, I'll go ahead and order up the KLX kit from Eagle Mike. Besides the allen screws for the carb, is there anything else I should think about putting on at the same time? I was poking around yesterday and found some mention of a metal replacement for that little plastic knuckle that the choke cable goes through — the one that breaks so easily — but I can't find the page again…
 

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If you haven't done the balancer lever you ought to. Just get the lever kit if you like; you can swing by here and use my tools.

The choke piece you're thinking of is by Stead Engineering. It's here.
 

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Discussion Starter #5 (Edited)
I will take you up on that, Tom. As long you're not a serial murderer using KLRForum to lure unsuspecting victims and their motorbikes to your lair… Could it be, this is the true meaning of the shed of horrors?? :surprise:
 

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Then . . . there's the knurled-knob fuel screw, or my preference: The T-handled fuel screw from Kouban!

Unnecessary, in my view, albeit convenient, the one time the fuel screw is adjusted (unless you're splitting time between Puerto Vallarto, Mexico, and the Nepal Himalayan Base Camp).

:)
 

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well, I was going to comment but Tom said everything that needed to be said. ......somehow I still managed to post though! LOL


Dave
 

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I suggest that Dave & Tom both forgot to say that the 22cent mod works fine on a stock air box or stock box minus snorkel.

But the KLX needle & main jet work best with the snorkel removed & 4 one inch holes or the complete "L" mod performed to the top of the air box.
Partly because the original dirt model KLX650 which these parts are borrowed from breathes thru a 6 x 6 opening in the top of the air box.
 

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good point about the airflow Paul though "fine" to me means "not as good as the KLX needle" Yes you need to remove the snorkle with the KLX kit but the data I've seen suggests that the KLX kit is better than the 22 cent mod even without the L mod or equivalent for the reasons Tom mentioned

Dave
 

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Discussion Starter #10
Yes you need to remove the snorkle with the KLX kit but the data I've seen suggests that the KLX kit is better than the 22 cent mod even without the L mod or equivalent for the reasons Tom mentioned
Thanks for the clarification. So it sounds like if I go with the kit, I'll definitely need to remove the snorkel, and there's more to be gained if I do the L mod as well, but the latter is optional. Right?
 

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Nothing about drilling the slide (or is that procedure considered part of the 22-cent mod)?

And . . . no one want to talk about a handy-dandy externally-adjustable fuel screw?

Or . . . did I perform the mods for NO VALUE AT ALL?????????

:)

I jest; I convinced myself the vacuum port enlargement in the slide is worthwhile (Samuel might profit from some discussion, pro and con); as I mentioned above, the conveniently-adjustable fuel screw makes sense (in my opinion) for the persistent tuner, or the rider of high relief (as in, thousands of feet) roads and trails. Otherwise, set it and forget it with an offset screwdriver or just a small flat-blade (again, my opinion only).
 

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Discussion Starter #12
When I first read your reply about the T-handle I was like, "what the farkle is that" but thinking about it today, I can see where this is pretty likely to be handy. It's on the list!

I was wondering how it works though… Does it just replace the bottom part of the jet, extending the driver out to where fingers can maneuver it without changing the position of the carb?

…and actually I would be into hearing the pros and cons for drilling the slide. I like the idea of "reversible," so my impulse would be against.
 

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1. Either the knobbed or the T-handled fuel screw works as you imagine; simply replaces the existing stock component (but mind all the tiny ADDITIONAL parts clinging to the stock item; save 'em and use 'em on the new screw). Again, you might never adjust this part more than ONCE; might fit into the, "nice but not necessary" box.

2. Drilling the slide IS reversible; through the magic of epoxy (e.g., "JB Weld," etc.) and a drill bit of the preferred size. Stand by for advice and analysis from other forum inmates on the merit/downside of slide drilling. BTW, drilling the slide does NOT affect air/fuel ratio; its promise: Improved/enhanced throttle response. Through custom and usage, slide drilling has become a no-cost component of the 22-cent mod for many; YMMV!
 

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The CVK40's slide is not directly controlled by the bike's throttle. The throttle cables open a butterfly valve. When the butterfly valve is opened the slide is subjected to the vacuum in the intake tract that is caused by the pistoned's downward stroke.

The hole in question allows the air that is above the slide to be sucked out, raising the slide by creating a vacuum above the slide. There is a long spring above the slide the resists its upward motion. The more the butterfly is opened, the larger the vacuum, so the higher the slide rises against the spring.

The size of this hole matters. Let's use an analysis of extremes. If the hole is tiny, say .001" in diameter, very little air can be sucked out from the area above the slide, so it cannot rise.

If the hole is huge, say the same diameter as the bottom of the slide, lots of air can be sucked out, but there is nothing for the resulting vacuum to act against and raise the slide.

Therefore, there must be a point where the hole has been enlarged as much as possible to speed up the rise of the slide (and thus throttle response) and making that hole larger would tend to make the slide rise slower because of the amount of area for the vacuum to act against has been reduced.

It would seem that Keihin have figured out a safe size that allows the slide to reliably rise at an acceptable rate, yet there is never any danger of the slide not rising at that rate or rising erratically. The tinkerers, on the other hand, have figured out that it can be opened slightly, to 7/64", and it will make the slide rise faster.

The pros are simply that throttle response is improved. As mentioned, the throttle is not connected to the slide, yet it is the slide the rises, opening the venturi and allowing more air/fuel into the intake. That's what makes horsepower. The KLR has a feeling of throttle lag. We optimists refer to it as 'turbo-lag'...

The downside is that, rarely, opening the hole can be a bit too much for that particular bike/engine/carb and rather than increasing throttle response the slide will flutter as it rises. That's not good as it has a rather negative effect on performance and feels like a dog poopin' tacks. As Damocles mentioned, the fix is to simply JB the hole and re-drill it to the OEM size.
 

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No doubt I'm mistaken, but I see no real benefit in THIS particular engine to speeding up how fast the slide rises. The whole purpose of the CV carb as I understand it was to keep intake velocity at the optimum level. If the slide opens too early and the engine hasn't already spun up enough, you lose velocity and get a lag in actual "engine" response.. I think some people equate throttle response to engine response and the two are different.
This is why those guys that put the 850 Holley on their 350 Chevys got beat off the line by the guy with the smaller cfm carb.. It's all about the velocity in the venturi. The higher the intake velocity, the more efficient it will be.
Has anyone ever done a dyno comparison drilled to not? Not just in HP but time taken to spool up from idle..
 

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iam hearing you Paddy, in my youth blokes used to junk Rochester Quadrajets and replace em with 350 Holleys, little did they know that by defeating the vacuum acceleration the humble Quadie could deliver a staggering 750 cf/m!
 

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No doubt I'm mistaken, but I see no real benefit in THIS particular engine to speeding up how fast the slide rises. The whole purpose of the CV carb as I understand it was to keep intake velocity at the optimum level. If the slide opens too early and the engine hasn't already spun up enough, you lose velocity and get a lag in actual "engine" response.. I think some people equate throttle response to engine response and the two are different.
This is why those guys that put the 850 Holley on their 350 Chevys got beat off the line by the guy with the smaller cfm carb.. It's all about the velocity in the venturi. The higher the intake velocity, the more efficient it will be.
Has anyone ever done a dyno comparison drilled to not? Not just in HP but time taken to spool up from idle..
Comparing the trick-carbureted (and sometime, OVER-carbureted), go-drive-fast engines of yesteryear, with the CVK40 of the KLR650, isn't entirely relevant, IMHO!

The problem with the GREAT BIG CARBURETORS was, insufficient venturi air velocity (and corresponding lame Bernoulli effect) to extract and properly "atomize" fuel, because of the too-large venturi cross-sectional area.

The PRIMARY venturis of most 4-barrel carbs were mechanically-controlled; the SECONDARY venturis controlled by intake manifold "vacuum." This mechanism remains a far cry from the CV (Constant Vacuum, or Continuous Velocity)-only CVK40.

An INHERENT DELAY in engine response to throttle opening resides in CV carburetors. REDUCING the time interval between the time the handgrip throttle barrel is rotated OPEN and the time the slide rises (permitting additional air/fuel mixture into the engine) remains the goal of HOGGING OUT the VACUUM PORT in the CVK40. The venturi pressure differential (or, "vacuum," if you will) may be transferred sooner to the mixing chamber above the diaphragm, consequently raising the slide sooner, if the vacuum port be enlarged.

Our Harley Brethren, some who use the similar CV40 carburetors, typically drill their vacuum ports to 1/8" diameter (perhaps their larger-displacement V-twins accommodate a vacuum port larger than is advisable on a KLR650). Additionally, some CV40 carburetors have ACCELERATOR PUMPS, whose function is to pump raw fuel into the venturi when the handgrip throttle barrel is suddenly opened; the raw fuel provides an instant fuel-rich air/fuel ratio, compensating for the consequences of a fast-rising slide permitting an air-rich mixture at the instant of throttle opening.

SLIDE carburetors (slides mechanically lifted) offer instant slide response to handgrip throttle opening, but . . . unless a calibrated accelerator pump accompanies the design, a "stumble" may occur when the throttle (handgrip throttle barrel) is opened suddenly. (BTW, just incidentally, the four-barrel automobile engine previously mentioned almost universally featured accelerator pumps.)

As to TESTING, performance with and without slide drilling, a somewhat complex proposition. First, I'd see NO DIFFERENCE IN STEADY-STATE DYNAMOMETER TESTING, because: Drilling the slide does not affect steady-state air/fuel ratio. As to COMPARATIVE RESPONSE TIME MEASUREMENT, a scheme of motion sensors and timing events would be required, seems to me. Worth it? Probably not!

Beyond the convoluted text above, I would suggest:

If a KLR650 rider is SATISFIED with his stock throttle response, and he willingly accommodates the inherent delay between opening the handgrip throttle barrel and engine reaction, LEAVE IT ALONE! On the other hand, if one feels enlarging the vacuum port REDUCES the delay just mentioned, GO FOR IT! Try it, but don't like it? As posted above, fully reversible.

REFERENCES:

Care and Feeding of the CVK40
Motorcycle Carburetor Manual, Shoemark, Haynes
Motorcycle Fuel Systems Handbook, Robinson, Haynes
And . . . most of all, LISTENING to men who know more about making engines run right, and go fast, than I will in a dozen lifetimes, in the shop and at the track!
 

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Interesting discussion. I'll try a different tact; brevity!

- drilling the slide affects throttle response not jetting so they don't have to go hand-in-hand.....many people do at the same time because thier jet kit instructions say so or because they already have their carb apart.....but they are separate things.

- If you're going to drill the slide, 7/64ths is recommended. 1/8" drilling was in the instructions for one of the jet kits (DJ?) but people have reported bogging at 1/8" hence the recommendation for 7/64ths


Me? I have the KLX kit on one KLR and a DJ needle with the same jetting on the other; both slides are undrilled as I didn't feel throttle response was a big problem for me.


2 cents,
Dave
 

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good point about the airflow Paul though "fine" to me means "not as good as the KLX needle" Yes you need to remove the snorkle with the KLX kit but the data I've seen suggests that the KLX kit is better than the 22 cent mod even without the L mod or equivalent for the reasons Tom mentioned

Dave
Thanks for the clarification. So it sounds like if I go with the kit, I'll definitely need to remove the snorkel, and there's more to be gained if I do the L mod as well, but the latter is optional. Right?
Yes & Yes.

I had hoped that my posting would suggest that if one is going to add more fuel to the mid-range with the KLX jet set, one should try to add as much air as possible to breath more freely like the non-EPA KLX dirt bike had, to get as much bang for the buck as possible.

I'll suggest that one needs to be extremely careful to get the thin rubber diaphragm sealing rib tucked into its groove when reinstalling the top cap. This usually the biggest error with this type of carb.
 
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Interesting discussion. I'll try a different tact; brevity!
BREVITY in post length, Dave? Hope I didn't challenge your ATTENTION SPAN, above! :)
Me? I have the KLX kit on one KLR and a DJ needle with the same jetting on the other; both slides are undrilled as I didn't feel throttle response was a big problem for me.
Dave
Makes sense! Truth be told, throttle response beyond OEM (stock) throttle response "brevity" would seem important, ONLY in COMPETITION, seems to me.

As in, geting the jump on your competitor when you power up coming out of a tight turn . . . don't think many wheel-to-wheel purpose-built competition motorcycle use CV carbs; no data nor reference, just my impression; contradictions, clarifications, and corrections always welcomed! :)
 
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