Hey everyone, This winter while my bike was off the road I decided to have a crack at a Mod a mate of a mate said to me a while back. The idea was to directly attach 4 pod filters to the tops of the carbs, getting rid of the ugly airbox and making the beast sound a little bit louder. I looked into K&N's but they were way to expensive at $80 each ($320 total) but I eventually settled on a 4 pack of DNA Oval Unifilters for 200 bucks. The filters are washable, are pretty much just like K&N's and look the ****. After this the rejetting saga began. Now my original jetting combo was... Size 10 Pilot Jets all cylinders Size 100 main jet Cylinders 1 & 4, Size 97.5 Cylinders 2 & 3 Jet Needles 5CT9 all clips set to center height. Stock Float heights IAW bike manual Stock airbox with stock Yamaha airfilter After about two dozen jet and needle height combinations I still had now joy in getting anything perfect. Every time I thought I had it almost perfect I would tweak something else and it would throw it right out. 1/4 throttle was very good, 2/4 & 3/4 was shocking, it was always to slightly lean or slightly rich and would never reach over 14,000rpm out of first gear. Full throttle still went hard but it was very rare that it would kick in out of 1st gear. The best jet combo I could manage was... Size 12.5 Pilot Jets all cylinders Size 102.5 Cylinders 1 & 4, Size 100 Cylinders 2 & 3 Jet Needles 5CT9 clips set to Center on Cylinders 1 & 4, 2nd highest clip on Cylinders 2 & 3 Stock Float heights x4 DNA Oval Unifilters Again, the midrange was very **** and a major frustration and letdown with this mod. The 3ln carbs seem to be ultra sensitive to air and really don't like it when you try to introduce more air into the system. Engine temperature from what I observed stayed normal for the most part. Iv'e never had the radiator fan activate on me since i've owned it though. I eventually gave up on the mod as it was just to frustrating and time consuming. I'm gonna have another crack at it next winter though, determined to get it working. I would seriously like to hear from anyone who has attempted this mod and succeeded. I have my doubts that its even possible now that I have had a decent attempt at it. Ideas regarding the matter would greatly be appreciated too. I had an idea of swapping the carbs out with FZR400 ones, is this possible and has anybody on here successfully implemented it on their bike? By the way when the Oval filters were on the bike it sounded MEANNNNNN. Might post some pics up, Ive got a running video as well if anybody is interested
First, from what I've read on the 400/600s, replacing the carb intake boots with pod filters does Bad Things, as the tract is now too short and you have resonance and anti-resonance issues. Adding a short piece of PVC pipe to increase the length back to stock often gives relief. Second, you went from stock airbox to individual pod filters and the best jetting was up ONE main jet size?! WTF did you use to oil these things - roofing tar?? <!-- s:-? --><img src="{SMILIES_PATH}/icon_Eyecrazy.gif" alt=":-?" title="Eye Crazy" /><!-- s:-? --> The filters should have just enough oil in them that nothing drips when you wring it; wet filters are useless. Check your notes, maybe try again...
I agree with dontz, you must have been running pretty friggin lean only going up one jet size. But I'd say the main issue is some weird resonance thing going on. The engineers at Yamaha would have spent some time getting the volumes and lengths of the airbox and intakes all good to make the engine breathe right. You just have to do the same. I bet it did sound pretty awesome though. I had my can off the other day and it sounded so sweet. Shame that riding it would mean melting my boot. Anyway, there will be a way to do it. You will just have to try different things. The fixed length tube could be a good option to try and get some sort of resonance going on in the intake. Good luck.
Im gonna go out on a limb here and tell you that replacing your your airbox with pod filters is impossible to tune. The reasons i say this are- 1. I worked in the 3rd largest bike shop in the country (New Zealand) for the better part of 7years and never saw/heard of/rode/came across ANY motorbikes that had done what you have done and been tuned perfectly. Even GSXR750/1100s, etc have a big flat spot that you just cant get rid of. 2. Ive never met a mechanic that has recommended this. 3. The smaller the engine, the more finely tuned and delicately balanced the tuned systems are. 250's are about as finely balanced (in terms of tuning) as it gets in the motorbike world. EVERYTHING is the way it is to make the bike run as well as it can. Cams, exhaust length/diameter/shape, airbox depth/shape/position, carb intake size/length/shape, valves, pistons, cylinders, head, absolutely everything is specifically the way it is to make the bike run awesome. Change one thing and you throw the whole lot out of whack. I agree that what Dontz says sounds like quite a logical way to overcome the airbox resonance issue, but i have very strong doubts that his idea will allow you to tune the bike. Basically, if you want poddys and all the "coolness" that goes with them (sound, kudos, whatever) then you're going to have to accept the negatives that go with it too (poor performance).
When i started modifying my FZR i wanted to do the same thing. Ditch the box and rock the poddys. I didnt for all the performance reasons. Instead i swapped out my crappy standard paper filter for a high-flow foam oiled filter (such as the hi-flo one which is awesome) and left the airbox lid off. Doing so upped my airflow and increased induction noise. Basically the bike goes harder and sounds better <!-- s --><img src="{SMILIES_PATH}/icon_biggrin.gif" alt="" title="Very Happy" /><!-- s --> I really highly recommend you try that instead. It works.
As Don says, the air ducts are designed to deliver a smooth air flow over the rev range that the bike runs at. Look at the latest YZF R1. They have an intake ram tube that is motorised so that it changes length to stay in the sweet spot. I believe this all happens inside the air box..
This is established wisdom for the larger bikes; I don't disagree that the little Fizzer is far more highly tuned (and thus twitchy), but it's a quick, cheap and easy correction to attempt.
As i think it has been made fairly clear, your problem is that you have removed your airbox. Your bike needs it, go put it back on and see what happens. Perhaps you could run the 4 pods into the box. Ive had a good read of a motorcycle performance book and it had very in depth explanations to airbox resonance and the like. It mentioned there was a fad when everyone ditched their airboxes in favour of pod filters, and then they all cried becuase the bikes were slower and ran like ****. The fzr makes good power for a 250. Just do a valve adjustment and ride the thing. Thats my advice. stay well
wow did this thread help me out heaps! i was going to put pods straight onto the carbs too like an idiot, the idea sounds great - MORE AIR! but if it loses performance - thats a HUGE no no. instead i will cut some holes in the top of the airbox - i hope that works. i just ordered a new jet kit and the specs like that matter alot and i just messaged the ebay seller about the new setup (not pod filters). i'm so glad to be on this forum <!-- s --><img src="{SMILIES_PATH}/icon_smile.gif" alt="" title="Smile" /><!-- s -->
I think some of the problems you are hitting here is that you are not mentioning that you are changing the springs in the carbs at all. If you look at things like dyno jet kits they come with carb springs, needles and jets. All are matched. Then you need proper dyno time to set them up. Without the springs they tend to just bog down on the throttle. My friend has a stage 7 gsxr1100 slabby running 4 K&N's and it runs sweet as a nut. No flat spots at all. Granted it makes less power low down than it did stock but it shifts like sh*t off a shovel further up. My FZR250 is stock and seems to hit a power band at 12000rpm, is that about right? God knows I wouldn't wanna ring its neck further just to get it to move. <!-- s:roll: --><img src="{SMILIES_PATH}/icon_roll.gif" alt=":roll:" title="Rolling LoL" /><!-- s:roll: --> Chris
does it rev any further than that (12,000rpm)? it shoud have opened it's powervalve (exup) fully at 10,000rpm and if you hold it open, it should want to rev upto it's 18.500rpm limit. On my model (3LN) the exup starts to open at 6k until fully open at 10k. a few times my exup has failed on me while riding it and the power loss was huge, but all i had to do to fix it was let the motor idle for 30 seconds or turn it off. i have only revved my bike upto about 17,500rpm a few times, my bike(1989 fzr250 3LN) likes to shift at 16,000 nicely, it feels like the revs will never stop <!-- s --><img src="{SMILIES_PATH}/icon_smile.gif" alt="" title="Smile" /><!-- s --> i bet it could rev to 19,000 if i let it lol
It revs plenty further than 12000, what I meant was the power kicks in alot at 12000, like a two stroke powerband. I just noticed today I have a small hole in the ehaust headers near where no1 cylinder joins the collector before the exup valve....... more to do lol. Chris
cool, i remember when i first started riding my FZR, i didn't know that it could rev to 18k and i only revved it upto 10k. when i got riding it more and more i found that it liked more revs at about the same time i found out the true rev limit <!-- s --><img src="{SMILIES_PATH}/icon_smile.gif" alt="" title="Smile" /><!-- s --> the way it climbs the tacho in 2nd gear is great, psycho in 1st gear tho. i hope the header hole welds up good for you.
Yeah I hope it welds up aswell, it's the only think I can think of that the bike will fail it's MOT on. Still, I have till near end of may for that. Went out today for a proper blat on it and it backfire through the hole on the overun. At low speeds it sounds like you have run over a cola can, at high speed it sounds like buckshot! Yee hah! <!-- s=0= --><img src="{SMILIES_PATH}/icon_2gunsfiring_v1.gif" alt="=0=" title="Gunfire" /><!-- s=0= --> Chris
my revs top out (the enging litrally cannot do any more) just past the 21k mark. but it sounds like it dosnt want to be done much... =p id say letting it go at 17 or 18 is best. as there is almost no extra power over 17. when im going round town and stuff i try and keep the revs down to about 12 though. so as not to deafen everyone.
my stock exup pipe is so quiet that it dosen't matter if i rev it up a bit, yr pipe sounds wild <!-- s --><img src="{SMILIES_PATH}/icon_smile.gif" alt="" title="Smile" /><!-- s --> i like how my fzr250 shakes slightly as you rage past 10k hehe, a bit of torsion vibration maybe but it's all good.
