gas mileage change - Kawasaki KLR 650 Forum
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post #1 of 24 Old 03-11-2010, 03:30 PM Thread Starter
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Question gas mileage change

Just wondering, anyone know how much of a change in gas mileage after doing the L box mod,.22 cent mod and pilot screw adjust ?
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post #2 of 24 Old 03-11-2010, 03:42 PM
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If you tune it properly and ride the same, none.

Efficiency is a good thing. More efficient breathing lets the engine spin easier. Less energy is consumed moving air within the engine itself, less mechanical effort is required to produce a certain amount of power.

Less mechanical effort means less air must be burned, requiring less fuel to burn it. Cruising at a steady speed will take very slightly less fuel than it did to cruise at the same speed previously, with all the restrictions. To realize this gain the carburetor must be tuned perfectly, unfortunately few are.

Most folks will argue this, as they lost mileage when they did the mod. Usually by trying one or two main jets, feeling more power and calling it good, setting the screw at some arbitrary number someone else used, and taking whatever fuel flow change happens from whichever size washer they happened to put on the jet needle. Most riders really don't understand the intricacies of carburetion, some don't even grasp the basic concepts of the different carburetor circuits. And of course there's the wrist factor, nobody does performance mods to a bike to ride exactly the same speed and use the same acceleration as they did before.

If hours and hours of experimentation (days and weeks really for those of us without a dyno) is done to get everything as close to perfect as possible, jets, needles, screw positions, slide cutouts, etc. your mileage could even improve, as the bike is tuned for emissions from the factory, not for maximum gas mileage. They are not the same.

Realistically your mileage will drop just a little bit, as even with all this perfection, if you choose to put forth that effort, in the end there is still the wrist factor.

Last edited by tkent02; 03-11-2010 at 08:17 PM.
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post #3 of 24 Old 03-11-2010, 04:17 PM Thread Starter
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thanks tkent02, I don't ride agressively, but do a lot of hiway, so I should be happy with some mods like these.
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post #4 of 24 Old 03-11-2010, 06:07 PM
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tkent02,

Spot on and very well put.

Tom

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post #5 of 24 Old 03-11-2010, 08:12 PM
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What Tkent and Tom said.
I've done all the mods and get 50 mpg when not hard on the main. (I used a 150)
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post #6 of 24 Old 03-11-2010, 10:05 PM
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L Box Mod

Can someone tell me what these mods are?
Thanks
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post #7 of 24 Old 03-11-2010, 10:20 PM
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L mod opens up the airbox intake, 22 cent mod uses 22 cent washers to raise the jet needle, adjusting the idle screw lets you tweak the idle and low power circuit in the carb. These mods, if done correctly basically let the engine run as well as it would if the EPA had no say in it.
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post #8 of 24 Old 03-13-2010, 07:37 PM
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.22 cent mod

Does anyone know if there is a posting where someone has done all of this airbox and carb mod and done pictures along the way to make it easier for us newbies? Also, where the heck is the snorkle located on these beasts?
Thanks
Intotheabis
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post #9 of 24 Old 03-13-2010, 09:45 PM
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Does anyone know if there is a posting where someone has done all of this air box and carb mod and done pictures along the way to make it easier for us newbies? Also, where the heck is the snorkle located on these beasts?
Thanks
Intotheabis
Not that I'm aware of.

The snorkel is way at the back of the air box on the left side. If you remove the left side panel you'll see it at the back, on the top of the air box. It can be a real sumbitch to get out.

The L-mod looks like this, and when done this way is easily reversed with 1" plugs:



You could also just cut an L-shaped hole instead of poking the holes. That hose next to the battery terminal has been plugged with a large vacuum cap. It was part of the CA evap system.

There are some pictures out on the 'net of the 22cent mod, I just can't remember where I saw them. Perhaps someone else will know.

Tom

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“The kid poured him another straight rye and I think he doctored it with water down behind the bar because when he came up with it he looked as guilty as if he'd kicked his grandmother.” -Philip Marlowe

“'Why' and 'How' are words so important they cannot be too often used.” -Napoleon Bonaparte

Sting like a butterfly.
Noli Timere Messorem

Last edited by Tom Schmitz; 03-13-2010 at 09:47 PM.
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post #10 of 24 Old 03-13-2010, 11:59 PM
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This subject is on my mind quite a bit as of late since I can't give a fact based
scientific explanation of the mpg's after the mods. One of the guys here on the forum
pm'ed me and wants to do a full tank side by side comparison ride/ hangout type thing.
Sounds like a great time actually and we may do it this summer.

It's just plain weird that in the early 90's the Geo Metro was advertising 58 highway
mpg, my Harleys both got 50 mpg's one with the 1200 engine, and the twin cam
hadda 1450 cc block. Those Geos had to be between two and three thousand pounds
yet we get the same 50 or slightly better mpg's with the KLR's when tuned carefully
for elevation and taking it easy on the throttle hand.

Why???

By doing the pcv mods I lost a LOT of engine braking under closed throttle
deceleration. That tells me the engine isn't working against itself so hard anymore.
With the intake and exhaust opened up the engine breathes easier, but requires
richening to compensate or risk detonating itself to death by holing the piston.

My engine is slightly richer on AFR, but revs freer and gets the same or better
mpg's. Then again, that wacky Metro is a cage and got the same mileage.
Why is our mpg the same after fattening the mix, and why can't we get closer
to 100 mpg's with our water cooled engines?

I'm obviously no rocket scientist, but intelligent enuff to understand basic
principles. It would be nice to have ammo for discussions like this.
Instead, I halfta say, "I dunno, it just runs better and doesn't use any more
gas than before." The 150 main is because the Great Lakes where I live is not
too far above sea level. (Maybe I should go down to 145.)

CheapMark
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