Kawasaki KLR Forum banner

New question, the Air box

15K views 41 replies 8 participants last post by  Grant S 
#1 ·
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?
 
#2 · (Edited)
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.
 
#3 ·
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
 
#4 ·
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.
 
#5 ·
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'! :)
 
#6 ·
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
 
#7 ·
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!
 
#8 · (Edited)
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
 
#9 ·
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
 
#12 ·
Something I have wanted to ask for a while. Does the L-mod require a clip position change?
Specifically I have a 2016 (Gen 2) with Std exhaust De-snorkeled KLX needle with clip in 2nd groove & the jet to go with it. If I do the L-Mod should I change the clip position?

Thanks
Grant
 
#14 ·
It is my understanding that the taper of the needle and the size of the needle jet are DONE by 7/8ths throttle.

So the Main Jet has full control by 7/8th throttle and if the main jet is TOO Rich it feels like the engine pulls harder if one 'Backs-Off' the throttle "just a hair", when revving to near Red-line. This drops the taper of the needle back into the Active 7/8ths zone.
 
#15 ·
It's my understanding that popping through exhaust is caused by a lean condition, but a rich condition can result in its more violent cousin, backfiring. Not sure if this can — or does — happen with the KLR, given that most of them run super lean, and then many lean them out more by opening up the intake and exhaust, but it's perhaps worth a mention because in closing up the hole in your airbox you restricted the airflow, and less air flow = richer mixture. If you're way, way rich on the jetting, perhaps that could be related. I'd be curious to hear:

• What pilot jet you have
•*Your idle fuel mixture screw setting
• What needle you have
• What main jet you have
• Whether your carb is clean (what's the recent driving history? Consistent driving with good performance and this just cropped up?)
• How does your bike run in general? Does it feel powerful/smooth/responsive?
- Does it idle at the same speed always or does that move around?
- How does the bike react when it's warm and you open the "choke?"

I will say that I recently experienced a super rich condition when taking my "tuned for power and smoothness at sea level (i.e. damn rich)" bike to 7000+ ft. I don't recall getting backfiring, but did have a host of other symptoms (bike dying at idle, laggy feel on the accelerator, general rough running, super smelly exhaust) that I addressed by lowering my KLR needle and stepping the pilot jet down. I would suggest taking inventory of other factors like these — are there any other changes in how the bike is running overall?

Here's my favorite tip to keep in mind when thinking about fuel mixture. Temperature of the engine has a huge impact on how the carb works. Obviously, OK. Well for me it was news to learn the reason engines need an enricher circuit: because fuel evaporation is a big part of carb operation, and because fuel in a hot environment dissipates into smaller particles more readily than in a cold one. Increased dissipation allows a given volume of fuel to burn more readily, owing to increased surface area of the fuel itself when it's spread out amongst a bunch of small droplets as compared to larger ones. This is why we have to dump extra fuel in a cold engine to get it to start, because the normal amount doesn't burn as well due to the fact that it's "clumped up" — i.e., because the mixture is effectively lean.

Alright skip all that and consider this: At startup, because it's cold, your engine is effectively running lean. Then as it gets warm, the mixture effectively enrichens. As it gets hot, the mixture gets effectively richer still. So, if you're wondering about jetting and where you are compared to where you want to be, you can get valuable clues by taking note of how the bike runs as it warms up. If it's running better (by your judgement, whether "better" means more power, less popping, smoother operation, etc.) cold, it's likely that your jetting is rich because your engine is effectively running lean when cold. Same vice versa: If your bike runs better in stop-and-go traffic, your jetting might be lean, because the bike is effectively running rich. I say "might" because, surely, there are other things that go into how the engine is running at different temperatures (things I really don't know about), but I personally found this to be a very handy way of working with carb settings (and not blurring the picture by messing with more than one thing at a time).

The same thing applies to air temperature. Good cold days can indicate that the jetting is rich. Good super hot days can indicate that the jetting is lean (if the goal is to run well on "normal" temperature days, anyway). Altitude and humidity also go into it. For all three of these factors (temperature, altitude, humidity), "higher" results in "effectively richer."
 
#16 ·
I'll suggest probably NOT.
Unless you are normally at less than 500m above sea-level (go 1 shim richer) or more than 2000m above sea-level (go #1 groove + 1 shim, leaner) .
Actually my bike lives about 2m above sea level and most of my riding is less than 100m above sea level, so I will keep this in mind when I get around to doing my first non-reversable mod. (cutting 4 one inch holes in the air box lid) Non reversable in the sense that every other mod I have done so far I have the original parts to put back in should I desire.
 
#17 ·
I appreciate all the input and information, I just haven’t had the time to even get close to the bike in the past couple of days. I’m sending my daughter off to college in less than two weeks, lots to do, a place to live, car, and everything else she needs to get out on her way. She’s my youngest child and this is really taking a toll on me, this is so much more difficult than I ever imagined it would be. She thinks she is so grown up, and all I see is that little girl running around in a diaper carrying her bottle and old beat up teddy bear.
Anyway I’m hoping to be able to dig into the carb this weekend and hopefully can provide some useful information.
 
#21 ·
"don't bother with the little 1" foam filters if you drill the holes - they are useless. "

Great information. I won't argue that the little 1" foam filters have any performance benefit at all, but the ones I have used in the past have a plastic cross hatch in front of the foam that serve as an effective mouse barrier. If you live in the country you have mice, that's just a fact of life. Every available hole in your bike is a potential invitation for them to come in a build a nest and feast on your wires and other tasty bits like your foam filter etc. I even keep a plug in my exhaust when the bike is parked in my shop and have sonic pest repellents in a few of my electrical outlets as well as various traps and other deterrents. Mostly the mice just mock me by leaving the occasional well placed turd on my tail rack so that I know they are watching me.
 

Attachments

#22 ·
good point; luckily I've managed to avoid mouse problems......but they could just as easily crawl through the much larger snorkle opening unless you plug or put screen over that too.

The reason I say the 1" foam filters have no benefit is because they block off at least half of the airflow you are trying to add......when they are clean. When they are dirty, I suspect that they have very little airflow through them at all which basically negates the reason for cutting the holes in the first place. Your main air filter is all that is required from a filtration perspective so IMO, adding those liitle filters undoes most of the work to add them and adds additional maintenance for no reason. If the mouse thing was a big concern for me, I'd use a hot glue gun and add some 1/4" x 1/4" screen over the 1" holes and the snorkle opening.

2 cents,
Dave
 
#23 ·
To update, I haven’t touched the bike for several days now. Too many other things going on right now. I did, however, order several items. I ordered and received from Eagle Mike the Doohickey and torsion spring, KLX needle kit and carb screw upgrade. I also ordered a new Shinko 705 front tire, Uni air filter, 1” handlebar risers, right and left hand levers, clutch cable, throttle cables, bought a new hard case for the tail rack, new handgrips, new chain and sprockets, oh and new screw insert kit for the front shield. I have a #42 slow jet on it way, also from Eagle Mike. Once everything arrives I plan to spend next weekend with the bike in my garage. I’d like to do it this weekend, but I’ve got to finish getting my daughter moved. I figure concentrating on the bike for a few days next weekend will help me forget about my empty nest depression.
 
#29 ·
Yep, the DRZ would be my next choice if I was to take one more step towards the dirt.... I spent some time riding one in Baja when they first came out, switching back and forth between a stock-ish 1992 KLR; the DRZ was a much nicer ride up the dried out arroyos. Tried one a few times since and I still like 'em.

Cheers,
Dave
 
#30 ·
I had a chance to do a little work to the bike this morning. I drilled and tapped the oil drain hole and put in a 1/2“ plug with a new crush washer. Nice and snug, and no leaks. Second I put in a new freshly oiled Uni filter, rode the bike for about 20 minutes, and the popping has been nearly eliminated. I only noticed one time I had a slight pop on deceleration, no more loud popping as before.
Next up is the KLX needle kit, hopefully this weekend, then the Doohickey, again hopefully this weekend. Probably should have done it when I drained the oil and tapped the drain hole, but I had very limited time today.
My plan is to complete everything I want to finish this weekend, then ride over to the Central Coast to visit my daughter. The upper 70’s will be a nice change from the 107 it’s supposed to be tomorrow.
 
#31 · (Edited)
I opened up the carb this morning to install the KLX kit from Eagle Mike. I found a #140 main jet, stock needle, that was shimmed with one washer, a #40 slow jet, and the mixture screw was turned out 3 turns from seated. I followed the recommendations from EM that came with the kit and put in a #42 slow jet, a #142 main jet, turned out the mixture screw 2 turns from seated and installed the KLX needle with the clip 3rd from the top and one shim. I also put in the Allen head screw kit from EM. I also put in a new plug while I had the tank off.
I buttoned everything back up and fired her up. She fired right up with no choke, I could tell the difference right away. Crisp throttle response, and the popping on decel is now gone, I couldn't get any popping on decel at all no matter how hard I tried. I am very pleased with this mod. I was hoping to put in the Doohickey and torsion spring this past weekend, but life got in the way and that didn't happen, unfortunately this next weekend is not looking good either. Once that is done, I have a new front tire to put on and a set of pannier racks to install and I'm ready to ride.
My wife thinks I'm crazy, and I might be. She says to me last night, you had a perfectly good bike that you rode everyday, then you sell it to get a bike that you have spent the past month working on all the time, why? I tried to explain to her, but she doesn't get it. I've owned more bikes than I can remember over the past 40+ years from Hondas, Yamahas, Harleys, Triumphs, even an Indian. But of all the bikes I've owned the 2004 KLR was my favorite. I sold it after my back surgery and have regretted it ever since. It wasn't the fastest, the or most comfortable but it took me on more adventures than any other bike I've ever had. I've had several since I sold the KLR, but have never been satisfied with any of them, they just didn't give me that feeling I got when I rode my KLR. So now I'm taking my time getting the bike just the way I want it and expect it will be with me for many years to come.
 
#32 ·
A question on the slow jet. Looks like I might have missed something when I installed the KLX needle.
I did the main jet change to 142 but did not touch the slow jet. As I am in Australia I did not get an Eagle mike kit. I got the needle & main jet by ordering from the local dealer.
Does not changing the slow jet explain the slight miss/hesitation I am experiencing at cosntant speed around 3200-3400 rpm. ?
Otherwise I am very happy, it is now a completely different bike to ride compared to the LAMS approved bike it started out as.
 
#37 ·
A question on the slow jet. Looks like I might have missed something when I installed the KLX needle.
I did the main jet change to 142 but did not touch the slow jet. As I am in Australia I did not get an Eagle mike kit. I got the needle & main jet by ordering from the local dealer.
.
Certainly some bikes will run better with the 42 pilot but you didn't miss anything and the KLX kit doesn't come with a new pilot jet. Both my KLR's are running the KLX kit with the stock pilot (142 main, 2nd clip position - no shims, 2 turns on the fuel screw). Mine have aftermarket silencers, snorkle-ectomy's, 4-1" holes in airbox top and Uni-filters.

Dave
 
#34 ·
IMHO, The pilot jet/slow jet DOES control the low speed mixture thru the 3 tiny holes at the bottom lip of the throttle plate, at the low rpm Cruising speed you are suggesting.
Are you 100% certain that those 3 tiny holes are 100% clean? They get 100% of their fuel from the pilot jet/slow jet as does the externally adjustable low speed mixture screw.

I close the low speed mixture screw in-order to view the aerosol carb cleaner sprayed up thru the pilot jet tower (jet removed). We need to see 3 nice round streams of fluid coming thru those 3 low speed transition openings. If clean, try a #42 pilot jet. Readjust idle mixture screw a little leaner.
 
#35 ·
Are you 100% certain that those 3 tiny holes are 100% clean?
I think they are clean which is not the same as following your instructions for checking. So thank you I will check.
Should I need the # 42 pilot jet.
For the idle mixture adjustment, I always get confused as to whether it is air or fuel that is is primarily affecting. Is leaner in?
Thanks.
 
#38 ·
Thanks Dave, good to know.
I am leaning towards making up a tool to adjust the mixture screw & trying it slightly richer. If nothing else it will save having to explain to my wife why I need to pull apart my nearly new bike again.
As this condition only appeared after I fitted the KLX needle & is still there now that I have added 4 7/8th inch. (because that is the size of the hole saw I had) holes in the air box lid, I don't think it is a blockage of the 3 holes in the btm of the throttle plate. But if a slight increase in richness of the mixture does not fix it, that will be my 1st check.
 
#39 ·
Hard concept to convey, but . . . the idle mixture screw dominates mixture only at idle and up to maybe 1/8 throttle opening, although--some insist the idle mixture screw remains critical up to wide-open-throttle redline. Maybe they're right, despite the, "Where The Parts Do Their Part" diagram! :)
 
#40 ·
Damocles,
It is definitely happening at one of the 2 main transition points. It is fairly low throttle opening. I have not had not had much time to ride lately to fully sort out the specifics, between wet windy weather & other time constraints. Weather report is looking OK for tomorrow so hopefully I will get some time to narrow down if not solve the issue.
 
#42 ·
Thanks Dave,
Found it is available in Aust. cost $45 including delivery.(ouch)It arrived yesterday, I will not be fitting it for a while.
Interesting the instruction on your link describes how to know if you need a bigger pilot jet. So that answered that question.

I adjusted the idle mixture screw from the 1-5/8 turns to 2 turns & finally got to take it for a ride last weekend. Hesitation pretty much gone.
Damocles - correction to my previously incorrect description. Problem was around 1/8 throttle just over 2000 rpm.

Unfortunately it looks like no more riding for me this year as I grabbed too much frt brake ( stupid error / bad technique) hit the bitumen hard & dislocated my shoulder.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top