K & N filter

db · Post by db » Fri Aug 03, 2007 2:10 pm

Anyone know if there is a K & N air filter that will fit the buddy and/or if it would improve performance?

ThisDude · Post by **ThisDude** » Sat Aug 04, 2007 12:41 am

You can do better. I hate k&n's so do all my dirt bike buddies. Contrary to their claims it lets the most dirt in your engine of any filter I've seen. You'll never see a professional dirt biker with one, in fact all my friends who put them in their sportbikes when I went to clean their filters I showed them this, I wiped the inside of their intake tubes and out came dirty fingers! BAD for the engine that dirt got in and that's for EVERY k&n install I've ever seen. Instead get a decent high flow foam filter like this from mrp

http://www.mrp-speed.com/store/product. ... 260&page=1

This flow lots of air and if you oil it right won't let any dust through and it costs less. One thing though is that high performance air filters make your scooter more sensitive to altitude changes and you will definitely have to rejet, it's not just bolt on and go. And theydon't offer much improvement if you're not at sea level. I learned this a while back from talking to the 50cc guys at urbanscootin. Turns out everyone who did an intake mod in like colorado or utah or other elevated areas didn't see any appreciable difference in power but coastal people did. Plus when I did intake stuff and went into the mountains at altitude I had less power than a stock airbox. Carburetors are just that senstive and those airboxes were designed that way for a reason plus you won't be getting all that much more power anyway.

Keys · Post by **Keys** » Sat Aug 04, 2007 1:48 am

However, as I've posted several times here, the Buddy uses a CV carburetor that is operated by the vacuum generated by the intake system. ANY change to that system, ie; the air filter, will result in a change in those vacuum characteristics. A change in those characteristics will equal a change in the operation of your carburetor. It will no longer be suited to either your intake system or your performance requirements.

Unless you are a carburetion guru, my suggestion would be to leave well enough alone. You could probably bypass that by using a slide throttle type of carb, but you would lose the performance benefits of the CV carb and would more than likely end up gaining nothing.

Changes to the exhaust system will not noticably alter your vacuum characteristics, which is why we can get away with that upgrade.

--Keys

ThisDude · Post by **ThisDude** » Sat Aug 04, 2007 3:04 am

A lot of people use uni filters on gy6 cv carbs, all you have to do is find the correct jetting and it'll work all right for pretty much one altitude. A CV carburetor doesn't work on the principle of vacuum, they use the vacuum to minimize altitude and temperature variances. The carb meters fuel on the principle of bernoulli's effect, regardless of vacuum. You can even supercharge a cv carburetor as long as you also give the same pressurized air through the slide assembly's intake, meaning you completely eliminate vacuum but it'll still regulate fuel all you'd have to do is find the correct jet to maintain the fuel air mixture across the needle. People put performance filters all the time on honda metropolitan 50cc engines with cv carbs without adversely affecting it's operation. But again getting the jetting right is what's gonna take up most of your time usually a good day of running and taking your carb apart to change jets. I'm all for adding power, I just don't need to on the buddy plus I take mine on mountainous canyon routes where a new low restriction filter would kill my power because of the change in altitude.

ThisDude · Post by **ThisDude** » Sat Aug 04, 2007 3:21 am

Oh one more thing that keeps me from changing the intake, it'll completely invalidate any warranties that cover my engine. Now that it's in for a bad crankcase seal I'm glad I didn't change it because I ran for like a week on less than half my oil, only 400cc's when I went to change it. I let it settle and I found no metal in it or any in the oil filter so I'm hoping for the best. I'll ride it lots of miles when it gets back just in case something went wrong when it ran low on oil, hopefully my engine doesn't blow up. And yes I analyze my used oil under a microscope if anything worries me or for break ins, just in case, so I can spot any potential problems.

KidDynomite · Post by **KidDynomite** » Sat Aug 04, 2007 3:52 pm

OK, I do not pretend to be a mechanic. I can certainly turn nuts and bolts, but I've never studied the why's of it all.

However, I am a bartender at an airport bar. I was talking to the personal airplane mechanic of a Major League Baseball team while they were in KC a few weeks back. I was talking about my buddy and he said he used to work for Honda before his current career. Said the test rides were too scary at 170-180 MPH.

I was initially asking him about changing my rollers while I replace my belt and he didn't recommend it, stating I'd just be robbing power from one area to move it to another.

Instead, he recommended a pipe, intake, and rejetting.

I told him about the Prima pipe and he said perfect. Get that but that it won't really make any difference unless I give it more air and eventually rejet.

He said this would give me more power throughout the power band and not only give better accelleration, but more top end as well.

I was on the verge of doing this until I read this thread.

I WANT MORE POWER!!! Not a lot, just about 10%.

Seriously.....if I'm in Kansas City elevation 700-900 ft.--depending on where in town you are--shouldn't I be able to gain with these mods?

Isn't the Prima pipe a worthless performance mod if more air flow isn't added on the front end?

db · Post by db » Sat Aug 04, 2007 4:51 pm

thanks for the info, what is "rejet" and how do you do that. Is that adjusting the amount of gas getting put in?

ThisDude · Post by **ThisDude** » Sun Aug 05, 2007 9:39 am

Oh all those bolt ons will only give maybe 4-7 mph on the top end acceleration will improve noticeably if, and this is a big if, you can get everything dialed in perfectly. When you change the intake and exhaust you change the powerband of the engine. You broaden the area "under the curve" as dyno guys will say meaning you'll get more acceleration but no real difference top end wise. This will take a lot of experimentation. Plan on buying all the main jets up about 120, stock is 90. And also buy several sets of different roller weights. As for rejetting it is simply taking the carb off opening it up and unscrewing the brass plug that is the jet and putting another different one in. Not as simple as it sounds though. Since with all the mods broadening the area under the curve, you'll most likely have to shim the carb needle, which can affect your main jet selection and the reverse is true also. I make shims out of aluminum soda cans. When you do that it can affect your jetting. You need a really good butt dyno and a knowledge of how a lean or rich engine sounds and even smells and a feal for fine tuning to get the jetting right or you'll either run lean (bad) or you won't get maximum power and your stop and go fuel economy will suffer from a rich midrange. All that work for a few mph isn't worth it for most people, plus the hit you'll take on altitude versatility. But if you wanna squeeze dem ponies ya gotta do what ya gotta do.

ThisDude · Post by **ThisDude** » Sun Aug 05, 2007 9:44 am

In the simplest terms jetting does affect how much gas goes in. But in a cv carb it's more about proportions since the amount of air will determine how much gas will be let in. The proportions can change though especially if you mess with the vacuum the intake is designed with. The exhaust won't really affect your intake vacuum and most people don't need to rejet with the prima exhaust even though it flows more. Maybe if you do extended high speed running or live in low altitudes you may need to rejet with just a pipe.

KidDynomite · Post by **KidDynomite** » Sun Aug 05, 2007 4:50 pm

ThisDude wrote:you won't get maximum power and your stop and go fuel economy will suffer from a rich midrange. All that work for a few mph isn't worth it for most people, plus the hit you'll take on altitude versatility. But if you wanna squeeze dem ponies ya gotta do what ya gotta do.

Yeah, I wanna "squeeze 'dem ponies." I could care less about stop and go fuel economy. I wanna get Buddyesque fuel economy while being able to get from the 'burbs into the city with power to spare or feeling like I have enough power for those old country highways.

Like I said, whatever I can do to get 4-7mph on the cheap is my goal.

Let me see if I understand this thread. I am in Kansas City, approx 800 ft. of elevation. I want to add the Prima exhaust and some sort of high flow intake.

I'll need to run it a bit WOT then do a spark plug check? Durring this process, I should also be checking sound and smell so that I can recognize lean vs rich in the future. I should be prepared to "jet up" until I find the sweet spot. I should expect the jetting process to be the hardest part of the process. For the most part, the Buddy's carb type should make this easier than some have said.

Please tell me where I'm wrong or off. If you are a make-believe expert, please don't comment. I want to hear from those who are truely in the know.

BlueMark · Post by **BlueMark** » Sun Aug 05, 2007 7:32 pm

well I'm not even a 'make believe expert' when it comes to carbs, but one sure way to add 5mph to your top end without having to touch the engine is to add a windscreen, even a small one. Aerodynamics baby!

ThisDude · Post by **ThisDude** » Mon Aug 06, 2007 2:39 am

Absolutely true windsreen will give you the most speed bang for the buck than anything. I've worked on modifying people's bikes, from engines as small as 23cc 2-strokes, all the way up to one liter superbikes. Not to metion helping some ricers squeeze ponies out of their cars. I've never seen a more ignorant superstitious bunch than those guys, I try to explain exhaust scavenging and intake velocity and vacuum to them, but they'll still insist on bolting on the wrong stuff like 2.5 inch tube headers (because they flow more) and small off brand "K&N" (they're trying to save some bucks, and it's got to be good if the box is covered in japanese writing, for all they know it could say "this filter sucks but I know you're still gonna buy it you stupid american bastard") airfilter instead of an oversize paper filter which flows more. And they'll wonder why their engine runs like crap. But all rants aside. You're pretty much right if you don't mind losing about 5 miles per gallon for stop and go traffic, to rejet all you'll do is put in the new jet and take off full throttle to top speed if you're engine bogs you're lean. When you get to the point where you have full acceleration you're close. Then what you want to do is go up one size and do a top speed test. When you do you should lose about a couple miles an hour off the top end compared to the previous jet but still have smooth accelration. When you get that, then you're running slightly rich. Back down one jet size and you'll be good, it may be slightly lean but these engines are designed to be run in a "lean of peak" mode for emissions and efficiency, plus when you're airfilter starts to clog you won't run excessively rich and end up losing more power. Then do some extended high speed running for about 15 minutes to let the plug color, when you pull it it should be light brown like the color of coffee with one cream, then you're good.

Now comes shimming the needle which is optional since it won't give power but only give back some efficiency, this is when you've got to be "one with you're bike" because you need to do quite a bit of low to mid level runs. When you do the mid-throttle running and you already jetted you may notice that when you stop you smell a faint hint of gasoline in your exhaust, if you want to confirm this have someone rev the engine mid throttle and press the rear brake to put a load on the engine (unless you've got a dyno, then use that) while the bike is on it's centerstand, then when he lets go of the throttle you should be able to smell the gas in the exhaust. Don't breathe too deep though lol. If you smell too much gas as in it's strong you need to shim the needle down and go up one main jet size. If it smells burnt like a barbeque that just got started on it's lighter fluid (that's the best I can describe it), you're running lean in the midrange and you need to shim the needle up and go down one jet size. After needle shimming you do another full speed run for 15 minutes and confirm that you're running good on the top end again, and doing one final rejet if needed. Again shimming the needle and, for the most advanced old school carburetor junkies reprofiling the needle, this doesn't get you any more power just regains some lost efficiency after power tuning.

It's a myth that whenever you add power you subtract efficiency. With a more powerful engine of the same size you don't strain the engine as much for any given power output and that means ideally it should be more efficient, in reality you just shouldn't lose efficiency. That was true of my metropolitan, no moped guys in my group could touch my speeds and those guys only got about 70 mpg while I cruised by at 110 and was still faster.