carb specialists - enlighten me, please...

Discussion in 'Technical' started by Klaus, Aug 16, 2007.

  1. What's a flatside carburator and how does it work differently from other sliders that are out there? When would you fit a bigger main jet and when a bigger diameter carb?
  2. Klaus,

    We don't mind helping but most of the questions you ask could be answered by yourself with a bit more surfing. You run the risk of "crying wolf" and then when you really need help....

    Flatslide does really make any difference for road use. They are a bit more "user friendly" when a really big carburettor is put on a racing bike.

  3. I could have done some surfing, yes, but usually I get a zillion websites in a lot of languages, then I have to filter the interesting looking ones, read them, and maybe I'll get an answer to my question. Sometimes I spend half and hour and don't find a satisfying answer. - If I feel it would be a question other riders would be interested in (everything you always wanted to know about your carburator) I ask the question in the forum. If we would google all the motorcycle related issues and keep our thus acquired wisdom to ourselves, the gt-rider forum would be a less interesting place.
    Also I like the opinion of experienced guys on a specific problem in a nutshell - I could google 'flatside carburators' for hours, learn all about them things, but the question would remain: Would it make sense to put one on my CBR150R? That's where the forum comes in where people exchange their experiences; maybe somebody bolted one on already and can post that it doesn't make much of a difference? Maybe his buddy put a bigger mainjet in his stock carb and the bike runs just as well as with a 3000 baht flatside carb? Or what about boring out the stock carb to a bigger venturi like I was advised by another CBR rider (who didn't do it, though) - ?
    Thanks for posting the info on carbs; what it basically says is that it would make sense to install a flatside carb on a bike with a big carb.
    (...take for instance a Honda XR100cc 4-stroke. They use like a 14mm roundslide carb for a 100cc induction charge. With a carb that small the vacuum signal is so strong that the configuration of the carb is not important. - Now take say an Aprilia RSW125cc where you have a 42mm carb for only a 125cc air charge passing through it....with a vacuum signal this weak you want the best possible throttle response.)
    See my point? Great info, but what would apply to a carb that's not 14mm nor 42mm but right in between?
    Why are hurricanes named after women? Because they arrive wet and wild, then leave with your house and car...
  4. I have fitted flat slides to Harleys and Ducatis, easy to tune and very fast throttle response,

  5. Carbs are a science of thier own, changing the carb alone to get better performance may cause you more problems than what its worth, especially to the inexperianced. Just bolting on another carb can have a domino effect, you then need to open up the ports to get the gas in and out again (another science on its own) get that wrong and your loosing power, then possably a cam to make the other mods work properly, then you need tougher valve springs so you dont punch holes in the top of your piston, then at the end of it all, whats been done to the bottom end of the engine to beef it up to handle the extra punch its getting from the top end. Once you have all this and your engine is screaming like a top and its life has been reduced by half, you then have to get used to your mates getting pissed off with you every time you break down on a ride because your engines reliability has just been halved as well.
    Sorry to be so negative but tampering with a stock engine just for street use is not worth it unless your planning on racing the bike, besides if you concentrate on improving the handling of the bike (suspension, tyres etc) you will find that you will be able to carry more speed through corners, which allows you to keep the engine up in its power range, hence better performance.
    I have a CBR 150 as well and i have been on rides with other CBR's and people comment that my bike flies but in a straight line thier is not a kilometer difference between all the other bikes, but when it gets into the twisty stuff it leaves the others for dead, because its very stable and it sticks to the road.
    If its arm wrenching power your looking for you may need to upgrade to a bigger bike, or go the NSR 150 2 stroke, you can really get one of them to sit up and go for very little expense.
    Iam not sure if this is true or not but someone told me that Honda Thailand may be releasing a CBR 250 I hope this is true because i will definately be getting one of them if it happens.
  6. There are a few already here. Like this one

    They are nice bikes,[8D] if a little revy.
  7. Took the CBR today on a 80km backroad trip where going faster than 100km/h would be suicidal, and thought to myself that the bike runs great the way it is. Of course it could have a bit more power, and my girlfriend could have bigger ears, but things are fine the way they are. Jonadda's post was a wake-up call, he's right about opening a can of worms, reliability problems and a shorter engine life.
    I was just looking for a nice sounding exhaust and got suckered in by all the aftermarket parts offered. But the bike is great the way it is; more substance in form of bigger rims and tires and a bigger front fork wouldn't hurt, or a better seat, but then it's only a 150cc bike for 65.000 baht. Can't expect much more.
    If I would do lots of highway riding I'd buy a 400Four with plates. Or a VTR 250, now that's a sexy bike. But I don't, so I'll keep my little CBR and bolt on a muffler so it sounds better.
  8. Don't be put off, it is fun to have a project and play with different bits, carbs,cam,valves, etc. They are not expensive in LOS. Just don't expect too much and do it for it's own sake. If you can feel the difference then it is worth doing. Depends on your "audience" if most of the guys you see on bikes are locals then having a trick local bike gives you street cred. If on the otherhand you want a bigger bike well.......

    My chicken chaser probably went from doing 95-100 kph to doing 115. Not a big deal but at every local bike shop I stopped at it got a lot of attention.
  9. Klaus
    Dont bother with bigger rims, if you compare a Moto Gp 250 to a Moto Gp 125 you will notice that the rims are a lot smaller on the 125s the reason being more rubber on the road, more friction, more weight, resulting in less horse power, this is critical when dealing with small bore motor cycles, when you have heaps of horsies its not so bad, besides the stock wheels have plenty of rubber on the road when tipped over, I have heard that IRC make a good quality tyre as opposed to the stock one you get on CBRs but i havent looked into it as yet, at the moment im running a Japanese Dunlop on the back and a vee rubber circuit competition on the front, at first i didnt think it would last too long being as soft as it is but it has suprised me and it really sticks, the rear shock is an after market gas shock made for those little KSR kawasakis, much better dampering, the only down side it bottoms out when you hit a bump 2 up but for solo riding its fantastic, cost about 2,800 baht, the front end i replaced the fork oil with a 10 weight oil, increased the oil level by 5-10 Ml from standard. and pre loaded the fork springs by about 20 Ml. By doing that it has given me the correct sag on the front for my weight, about 70 klg. I wouldnt try preloading the front springs much more than that as it may be too much for the stock spring and then bottom out.
    From what i hear the after market upside down forks are more cosmetic than practical, so i havent bothered with them.
    Have you heard of a good quality front disc for the CBRs, i think the stock ones are made of poor quality material, mine is not bent but i think it has soft spots in it and it is not wearing evenly giving me the feel of a bent disc, i have ridden some rental CBRs that feel the same, but dont look bent either.
  10. The CBR 250 Im reffering to is to be manufactured here for the Thai market, just like the 150 was, I really do hope so.
  11. After fiddling a few years with bikes on a non-professional level I realized that those boys at Honda (or any other maker) know what they are doing, and some of my 'improvements' were actually achieving nothing or even the opposite. Of course there are situations where for financial or environmental reasons bikes are restricted, and a little change can definitely improve things, like on my DR650 that backfired downhill in stock form and ran way better after drilling out the main jet and putting a bigger one; putting on better tires or top-of-the-line brake pads and lines never hurts, but when it comes to improving power or the suspension you better know what you're doing, or you throw a bunch of money at above mentioned 'improvements'. And to be honest, I'm a backyard mechanic who's willing to try something out, if others say it's worth doing it. But if I look at my CBR, it's only a 150cc bike, goes about 140 top, has a 11:1 compression and revvs to 11500rpm - what's there to improve? If you really want to make it go 170 with a big bore kit, hot cams and a screaming exhaust, you should consider buying a bigger bike.
    I'll install a good-sounding muffler and that'll be it!
  12. jonadda, when I mentioned bigger rims and tires and a beefier fork, I wasn't talking about trying to install them on the CBR. The superlight CBR (only about 20 kilo more than a Wave!) is like a mosquito on the highway, and a bit more weight and riding comfort wouldn't hurt. But then I'd go for a 250. There are two different CBR 250s, there a 250 single and the 250RR with a inline four that revvs to 21000rpm! Someting in between would be nice, the RR weighs 150 kilo, too much for a 250. Not much info here but a picture of the single: ... ?mmid=2661
    The 250/4 is of course a racebike and looks like one: ... rms=xr650r

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