New question, the Air box - Kawasaki KLR 650 Forum
2008+ KLR650 Wrenching & Mod Questions For repair, maintaining or modifying discussions related to the newly updated 2008 and beyond, Generation 2 KLR650 Motorcycle.

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post #1 of 41 Old 07-29-2019, 11:03 PM Thread Starter
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New question, the Air box

I had posted in my thread regarding the oil bolt that my airbox has a hole burned on the bottom. I repaired the hole with high temp plastic epoxy. One of the issues I was having was a slight pop on deceleration. Now that I have filled the hole, I am getting even worse popping, loud popping.
There are no mods to the airbox but the snorkel removed.
It’s been a few years since I’ve tinkered with the air/carb on a KLR. But my recollection is that when I increased the jetting, I opened up the airbox by drilling with a hole saw in the top of the box increasing air flow.
I’m thinking I plugged up the airbox by fixing the hole and creating a more lean condition? Thoughts?
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post #2 of 41 Old 07-29-2019, 11:12 PM Thread Starter
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I guess I should mention, the bike has and aftermarket FMF exhaust, PO said it was jetted for the exhaust. I guess I’ll open the carb tomorrow and see what the jetting is.
I also noted that when I used the enricher the popping became almost unnoticeable, so I don’t know, I’m tired and maybe just need to walk away and collect my thoughts and start again tomorrow.

Last edited by Niteryder; 07-29-2019 at 11:32 PM. Reason: Add text
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post #3 of 41 Old 07-30-2019, 11:25 AM
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As you are probably aware, the Gen2 KLR has an AIS system that pops on decel as a function of it's design. An aftermarket exhaust makes the pops much louder and I suppose chaning the airbox configuration could affect things as well.

removing the snorkle is a "bare minimum" mod for rejetting (as recommended by Eaglemike) but there is no real downside to doing the "L-mod" or 4 1" holes in the top of the airbox (dirty side only!).

Since you don't know what jetting or needle you have, I'd suggest you are on the right track by starting there.

Cheers,
Dave
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post #4 of 41 Old 07-30-2019, 08:23 PM
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A quieter muffler will dampen the popping. A louder muffler will Amplify the popping.

Richer LOW speed / Pilot jetting will reduce the popping, at the expense of fuel economy and possibly actual performance. You might ought to check the little de-celleration anti-afterfire Diaphragm on the LH side of the carb (air cut-off valve). A tiny pin-hole will cause decreased effectiveness.

Many V-Twin riders apparently prefer performance to go with their NOISE.

pdwestman
Modify at "YOUR OWN RISK"!

Still riding my 1987 KL650-A1. 84,000+ miles & counting
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post #5 of 41 Old 07-31-2019, 04:56 AM
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Generally speaking, anything fuel-weakening the mixture exacerbates (makes worse) deceleration popping. Hacking up the air box and/or installing a less-restrictive muffler fuel-weakens the mixture.

Kawasaki provides an OEM (stock) countermeasure, the air cut valve/coasting enricher/backfire preventer mentioned above. Intake manifold vacuum acts on this device's diaphragm, consequently fuel-enriching the mixture during deceleration. (q.v., Care and Feeding of the CVK40.)

Also, turning the idle mixture screw counterclockwise, fuel-enriching the idle mixture, may reduce the popping on deceleration.

All-in-all, some popping on deceleration ain't necessarily no thang, IMHO.

BONUS DISCUSSION QUESTION: Can anyone quantify (by actual measurement) the performance effect of hacking up the air box?

ADDITIONAL DISCUSSION QUESTION: Same as above, but . . . with "pod" air filters?

Just askin'!

“You better put down that gun. You got two ways to go, put it down or use it. Even if you tie me, you’re gonna be dead.” "John Russell" (Paul Newman), Hombre
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post #6 of 41 Old 07-31-2019, 10:13 AM
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Quote:
Originally Posted by Damocles View Post
BONUS DISCUSSION QUESTION: Can anyone quantify (by actual measurement) the performance effect of hacking up the air box?

ADDITIONAL DISCUSSION QUESTION: Same as above, but . . . with "pod" air filters?

Just askin'!
From KLRCary;


A lot of missunderstanding with airbox issues.

First, the screen. Airflow gains are not linear. Removing the screen with an otherwise stock KLR airbox will only gain you 2 cfm. The engine won't know the differance. However, with a heavily modified airbox, the gain from removing the screen is 8 cfm. Depending on what else is done to the engine, you may make more power. I doubt that you'll feel it, but a dyno will show it. Butt-dyno's can detect very small low rpm changes, but don't detect higher rpm changes very well at all. You'll likely not detect it, but that does not mean it's not there.

Comparing screen removal to other models is wrong, particularly with the newer sportbikes. With them, the screen often serves another purpose as well. Air distribution in a 4 cyl sportbike can be a real problem, particularly with "ram air". Removing the screen on them can cause very real losses, depending on the model. That does NOT apply to the KLR.

Same thing with air filters. There is only about 2 cfm differance from the best filter (UNI), to the worst (K&N). With a modified airbox, that differance grows to 9 cfm.

Here is the flow chart:

Completely stock - 64.8cfm
Same - Remove snorkle - 74cfm
Same - With UNI filter - 76.2cfm
Same - Remove screen - 78.6cfm
Same - Small "L" cut - 85.1cfm
Same - Large "L" cut, open snorkle area further - 92.4
Same - Remove door - 103.2

Alternate - UNI filter, No snorkle, With screen, No door, No "L" cut - 95.4

All at 2" of water, tested at 1 1/2" and 3" and averaged to 2"

To answer the larger question, how much air can the KLR really use?
....................
A stock KLR about 70-80cfm. With a good pipe about 75-90cfm. A modified motor about 90-100cfm. Having a bit more capacity than you you need will not hurt anything. The effects are not linear though. Going from 65cfm to 75cfm you will likely notice, but going from 75 to 85 cfm you likely won't.

Part of the confusion might be due to the effects of the carb shimming. Since that mod is for a stock needle, the snorkle removal serves not just to add air, but to lean out the top end. The stock KLR till 07 is rich on the top. ( The 08 has a smaller main jet.) Airbox mods have much more effect on top end mixture, so, with the stock needle it also helps straighten out the fuel curve.

Finally the airbox door. You've got to carefull there. You don't have clean air there. It's flowing past that door when riding. You can easily create a partial low pressure area there, depending on wind direction, and where you place your leg!

Cary"


I do not recommend removing the backfire screen (PITA) or running without the airbox door for reasons that should be obvious.

Though a KLR isn't going to have a bunch more power no matter what you do, a KLX kit combined with the snorkle-ectomy and L mod or 4 - 1" holes will have it running properly. don't bother with the little 1" foam filters if you drill the holes - they are useless.

Cheers,
Dave


From KLR Chris (note that the testing methods differ so the actual numbers aren't comparable to Cary's work but the results are basically the same) https://www.klrchris.com/kawasaki-klr650-airbox-mod/


I've never bothered investigating a Pod filter because using one destroys the ability to use the bike as an actual dual sport so it has no interest for me.....plus it would appear that the L mod, snorkle-ectomy and Uni-Filter can support the amount of airflow required for a healthy KLR with jetting, silencer, 685, etc.


Dave
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post #7 of 41 Old 07-31-2019, 12:03 PM
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Thanks for sharing KLRCary's data and comments, Dave!

(A footnote: "willys," a one time poster on this website, claimed to have KLRCary's notes, but with no provenance nor examples shared. Other sources indicate Cary's notes were provided to Eagle Mike after Cary's death.)

You mention KLRChris. KLRChris claims, with a bone-stock (no big-bore kit, no trick cam, no porting, stock valves, etc.) KLR650, he achieves (on his dynamometer) a 20 % gain in rear wheel horsepower by the modest and inexpensive modifications of: a KLX needle, 142 main jet, air box mod with 2/3 door removed, FMF Power Bomb and PowerCore4.

I struggle, grasping for the operational mechanisms enabling this profound increase in horsepower, with the economical and simple modifications performed.

If the Law of Conservation of Energy applies, power generated remains a function of the quantity of fuel processed per unit time. Thus, I fail envisioning 20 % more fuel flowing through a main jet whose diameter is smaller than stock configuration. The air box mod and aftermarket muffler reduce flow restriction; the needle fuel-enriches mid-range operation; and . . . looks like the smaller main jet would fuel-lean wide-open throttle operation, to me, but . . . I may be overlooking factors obvious to experienced tuners.

Again, thanks for sharing the enlightening discussion about the air box!

“You better put down that gun. You got two ways to go, put it down or use it. Even if you tie me, you’re gonna be dead.” "John Russell" (Paul Newman), Hombre
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post #8 of 41 Old 07-31-2019, 02:18 PM
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Originally Posted by Damocles View Post
Thanks for sharing KLRCary's data and comments, Dave!

(A footnote: "willys," a one time poster on this website, claimed to have KLRCary's notes, but with no provenance nor examples shared. Other sources indicate Cary's notes were provided to Eagle Mike after Cary's death.)

You mention KLRChris. KLRChris claims, with a bone-stock (no big-bore kit, no trick cam, no porting, stock valves, etc.) KLR650, he achieves (on his dynamometer) a 20 % gain in rear wheel horsepower by the modest and inexpensive modifications of: a KLX needle, 142 main jet, air box mod with 2/3 door removed, FMF Power Bomb and PowerCore4.

I struggle, grasping for the operational mechanisms enabling this profound increase in horsepower, with the economical and simple modifications performed.

If the Law of Conservation of Energy applies, power generated remains a function of the quantity of fuel processed per unit time. Thus, I fail envisioning 20 % more fuel flowing through a main jet whose diameter is smaller than stock configuration. The air box mod and aftermarket muffler reduce flow restriction; the needle fuel-enriches mid-range operation; and . . . looks like the smaller main jet would fuel-lean wide-open throttle operation, to me, but . . . I may be overlooking factors obvious to experienced tuners.

Again, thanks for sharing the enlightening discussion about the air box!
No Problem. Comments;

- yes, Mike told me he has Cary's notes.

- I've thought that KLR Chris' results were much better than expected (I'd have guessed 3-4hp) but he seems to know what he's doing and has gone to the trouble of testing everything so I'm going to take it at face value.

- the main jet may be smaller but the needle is richer as is the overall jetting (despite the smaller numbered main). Keep in mind that the jet and needle work together and you cannot compare jet size without considering the needle used. To put it another way, the KLX needle is thinner (for the most part) and that means it allows more fuel through the same jet as the stock needle would.

edit; I tried posting pics of the needles but it wouldn't show for some reason.


2 cents,
Dave

Last edited by DPelletier; 07-31-2019 at 02:21 PM.
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post #9 of 41 Old 07-31-2019, 03:51 PM
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Originally Posted by Niteryder View Post
I’m thinking I plugged up the airbox by fixing the hole and creating a more lean condition? Thoughts?
No, plugging the hole in your airbox did not create a more lean condition.

So, when did the popping on deceleration first start? What's the position of your pilot/slow/idle jet needle? Mine is about 1-3/4 turns out from lightly seated. Anything less than 1-3/4 turns may cause popping upon deceleration.

Jason
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post #10 of 41 Old 07-31-2019, 04:52 PM
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Quote:
Originally Posted by DPelletier View Post

- the main jet may be smaller but the needle is richer as is the overall jetting (despite the smaller numbered main). Keep in mind that the jet and needle work together and you cannot compare jet size without considering the needle used. To put it another way, the KLX needle is thinner (for the most part) and that means it allows more fuel through the same jet as the stock needle would.
Good points, but . . . I thought the needle was essentially retracted completely from the main jet at wide-open throttle, where maximum horsepower readings register.

If the needle extends into the main jet at that point, I stand corrected, and understand how the entire needle profile affects mixture (even though the "Care and Feeding" diagram shows the main jet dominating mixture at higher throttle openings).

(I'd post the diagram (Again! ) but I'm into what I hope is momentary computer problems.)

“You better put down that gun. You got two ways to go, put it down or use it. Even if you tie me, you’re gonna be dead.” "John Russell" (Paul Newman), Hombre
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