hey all after reading a thread on the overclockers forums, im intrigued by the idea of getting a smaller front sproket and bigger rear sprocket... firstly, has anyone done this? what are your thoughts on the mod? and how many teeth did you gain/lose? cheers simon
Here's a website, near someone over/down there, that has a gearing calculator. http://www.metroyamaha.com.au/Tools/tools.htm 1 down on the front is = to about 2 or 3 up on the rear. By doing either or both, you will effectivly decrease your top end, but will increase acceleration. The inverse is also true, but I'm unsure of the gearing differences. Going up on the front or down on the rear increases top speed, but sacrificing accleration and torque at the higher RPM's.
thanks FZR Dude so it doesnt matter how many teeth you add to the rear and drop on the front? can you use any combination? or is there a particular way to figure out how many teeth you need to add to the back when you drop one tooth on the front? im in need of new sprockets so i thought i might investigate this before i go and buy standard stuff.... cheers simon
As long as you are going to do things sensibly you should be ok. Use the tool above to see what you think you should do (i.e. what results do you want to get?). There are no real rules regarding the increments/decrements that you apply (except for the fact that the sprockets must fit on your bike). Just remember that the fzr250 already requires very frequent gear changes, and if you drop the front and increase the back these will become even more frequent. Normally people only think of sprockets increasing acceleration and reducing top speed (and vice versa) and don't think about the impact it has on gear changing etc. It will also mean that cruising along at 100 k/hr in 6th will probably put the revs to 12 or 13 000 rather than 10 500 - i.e. increase fuel consumption... As a question - the guys on overclockers - are they talking about bigger bikes or 250's? I know of a few people who have done this change on bigger bikes because they don't see the reason being able to do over 100 k/hr in first gear, but haven't heard of anyone changing sprocket size on a 250 (except in one case where he increased the front sprocket and decreased the rear because his bike would not reach 110 - he was on an old virago 250).
It was on a 250, on a zzr250 if my memory serves me...he was talking about being able to do crazy stuff such as lift the front wheel with minimal effort from take-off...not my idea of fun but anyway... Hey Boz - I've seen a lot of the stuff you've put up about the exup valve, and I'm thinking that the exup is giving me some probs on my FZR250 3LN-3. Because I've had a rattle at idle since getting the bike, and have been told it was in the exhaust, I used your instructions and disassembled the valve. I had been told I should be able to tighten it up with a few washers, but couldn't see how that was going to fix anything so just cleaned it up with wd40, scraped off the carbon and decided to put it back as it was. For some reason it seemed overtight for a while (when I flicked the switch and the exup motor did it's little calibration, it seemed to labour slightly, made a different noise) that seems to have corrected itself pretty quickly though, I made sure. Anyway, even since before this, it's had an ongoing intermittent problem of stalling when the engine's quite warm and I'm idling (like when I stop at traffic lights after riding about 25 k's. In these situations when I take off from a standing start, unless I rev it quite high it will sputter and stall too. It's never given me any probs once it's running though (except that once or twice it's felt as if the back-pressure has built up and it's not accelerating smoothly). Anyway, what I really would like to fix is this stalling prob. Does it sound like exup to you? or have I made a mess of explaining it...?
Sounds like the problem you are having is one that I had for the last 10 000 k's on my fzr. From what I figured out it was primarly due to the carbies (running a bit too rich) though the exup excacerbates this... The problem I had was (and I am describing it here just to make sure our stories are the same) I would cruise at a relatively constant rate with revs around 8000 for a moderate length of time (5 minutes) and when I pull up and stop and then try to go again the bike really labours, and quite often stalled. As I said the primary source of the problem is from running slightly too rich (if you check your plugs likely you will see some fouling). My understanding is that since it runs a little rich the amount of exhaust being released at idle (exup closed) is not in proportion to the amount of exhaust (backpressure) being built up. So when you try to leave you can not get enough air into the engine to mix with the fuel to be ignited by a spark... Heavily revving it to take off actually opens the exup valve and thus release some back pressure, allowing teh bike to run. There are 3 solutions: 1) best solution is to get your carbies looked into (cleaned and jets adjusted). I have been told that on the smaller sports bikes the jets tend to get worn, and as they become worn they begin to allow more fuel through, causing richness. So you may (and it is probable) that jets would need to be replaced as well. (people on this site have indicated that accessing and adjusting the carbies on the fzr250 is not that bad) 2) alternative solution (cheap and easy) - adjust your exup valve such taht it is slightly open at idle. Usually when adjusting the valve you line it up such that the 'fork' is lined up with the whole in the exhaust. If you line it up so that it is slightly open this will help alleviate the back pressure problem. (You can also run with the exup wired fully open - there will be a slight loss of low down power but nothing too significant). 3) when travelling along every once and a while engage the clutch and blip the throttle so that the revs reach 12 - 14 000. This will effectively release any back pressure that has started to build up, and thus when you pull up at a stop you are starting with a engine with no back pressure. (if it is a long set of lights you may even want to blip your throttle while at lights - people may look at you funny though...). I always made sure to blip the throttle as I was approaching a stop. I should note: when I would do this while riding the bike would sometimes have a sudden dip in revs, but then it would pick back up soon after so don't be surprised if that happens. I never did solution #1 - I knew I wanted to sell my bike and could not be bothered with the time and money to adjust the carbies (and I hate paying mechanics). I didn't think I would have kept it for another 10 000 k's though... I did do #2 and #3 - neither were ideal and the problem was still there, but I learned to deal with it. The one side effect to #2 and #3 is that it doesn't target the source of the problem and the problem does continually get larger (i.e. jets get more and more worn). Eventually you will probably need to replace your jets. With all that said - #2 and #3 work well in combination. While it may not be the permanent solution it will see you through some time until you can arrange to have your carbies dealt with (or do yourself)...
the thread from overclockers was a gpx250, suppposively he was still able to reach the same topspeed he had with stock sprocket's, only that he gets there faster with the modded sprockets, theres also a clip of him doing power wheelies on first, i'll try and see if i can find the link. here it is: <!-- m --><a class="postlink" href="http://www.users.on.net/~Az1/vidz/MOV00645.MPG">http://www.users.on.net/~Az1/vidz/MOV00645.MPG</a><!-- m -->
man if thats a gpx250 i bought the wrong bike!!! must be some kind of power increase to get it to pull wheelies like that <!-- s:-? --><img src="{SMILIES_PATH}/icon_Eyecrazy.gif" alt=":-?" title="Eye Crazy" /><!-- s:-? --> - gpx's i've seen have been pretty gutless, especially compared to a fizzer
well like the thread title says "Larger rear sprockets", the Gpx had few teeth taken from the front and few added to the back, hence the better accleration and wheelies. I might consider doing this to the fizzer but gotta do some research first to see any downsides .. mainly fuel, but thats not a major prob.
Lowa that is a nice red FZR. Looks just about identical to mine. You gotta come out on the ride I am organising, it will look awesome! <!-- s --><img src="{SMILIES_PATH}/icon_cool.gif" alt="" title="Cool" /><!-- s --> Is that a 3LN or 2KR?
