Newbie Question about performance

Quick question for anyone who knows anything about motorcycle
mechanics.

Can replacing a carburetor with one from a bigger engine increase the
performance of the bike? A friend suggested it to me, but I'm not
quite sure if I believe him, so a more reliable opinion would be
nice.

Cheers
Vicky

 

Yes, get the carb off the biggest bike you can find, ones from twins go
particularly well on fours (you just need to prise them off 2 bikes).

At the same time go and ask your local bike dealer for a set of race jets,
these are extra slippy and allow more fuel across them.

 

IMHO it's not something to be attempted lightly. Assuming it bolts
straight on it'll still have to be professionally rejetted. You may
get more top-end power, but at the expense of torque at lower revs.
Plus you'll need to declare it to your ins. co. which may put up the
premium.

 

Yes, but it depends on the bike. The simplest way to increase power on a
Nordwest is to replace the OEM twin choke (one slide , one CV) Teikei
carb with two Keihin CR smooth bores. They need setting up though.

On little 50cc auto MX bikes a bigger carb it is a quick tune up route
too as they are often very small in novice trim.

Generally though, as others have said, I wouldn't recommend it to a
newbie.


--

+-------------------------------------------------------------+
| Pete Fisher at Home: |
| Voxan Roadster Gilera Nordwest Yamaha WR250Z |
| Gilera GFR * 2 Moto Morini 2C/375 |
+-------------------------------------------------------------+

 

If you're talking about a bike with one carburetor, then you're dealing with
kit at the very bottom of the performance food chain, and, honestly, wasting
your time. You don't say what your bike is, or whether you've got a full
licence. If you're a learner, the quickest and most sensible route to more
performance is to pass your test and get a bigger bike. If you've passed
your test, you're probably limited to 33bhp anyway. If you're legal for
full-power bikes, and you're still chuntering around on a single, you need a
Gixxer thou. The more information we have about you, the better we can help
you. For instance, do you take it up the arse?

 

It can do.
There was a time when a GSXR750 had bigger carbs than the GSXR1100
so putting 1100 carbs on a 750 would make it much more rideable.

Fitting the right size carbs is a good idea, as is using carbs that
flow properly, eg Dellorto or Mikuni Flatslides, rather than the nasty
CV carbs that most manufacturers use.

You need to consider the whole engine - valve sizes, compression ratio,
port profiles, exhaust diameter and tuning, cam timing and airbox
as well as the carbs.

Try a good tuning book such as
http://www.amazon.co.uk/Four-stroke-Performance-Tuning-Practical-Guide/dp/1844253147

What's the bike?

And as you're a newbie, are there any pictures of you naked on the internet?

 

"Speed's just a question of money. How fast can you go?"

 

Yes, but usually only as part of an overall tuning exercise.

(for example - more fuel/air in needs a way of getting more exhaust out,
so bigger exhaust, and you need to be able to flow the gases in and out
faster, so bigger valves, lifted open further and longer by a different
camshaft... you get the picture?)

Some bikes are under-carbed, though.

 

Typo corrected

 

<bows>

 

If you're talking about general-use commuter type things, yes.
But...
Only if the engine left the factory in a strangled state of tune.

Fing is - most bike engines are a work of engineering art and it's
cheaper for a factory to build many models based on the same engine but
with a variety of power outputs than it is to make every model's engine
different.

In some cases you will find the bike was sold with a smaller carb than
it was originally optimised for - perhaps to comply with power
regulations in certain markets, or simply because it was a cooking
version of a sportier model.

In those instances, yes, there might be a simple power increase to be
had by fitting bigger carbs (suitably jetted), but often you may have to
fit different cams too. And other stuff.
--
Dave
GS850x2 XS650 SE6a

Teach a man to fish and he and his pikey mates will have the
river cleaned out in a day.

 

LOL! There is a very fine line between information that is useful and
relevant, and information that isn't. I think somewhere in that
sentence, the line was driven over in a large 4x4, then reversed over
just to make sure. Then possibly trampled over for the heck of it! :-D

Back to the subject - thanks for all your replies. In answer to the
more serious questions - The one I've got at the moment is mainly for
passing my test (next month I hope!) and the insurance is cheap on it.
Friend mentioned it as he did it to his trial bike and suggested I do
the same. So the gist of it is that it's only really worth it with a
twin carb then?

Money is the real issue though - if I had enough of it I'd already
have bought my (other) friend's bandit 600 he's selling, and it would
be sitting in a garage waiting for me to pass my test. Alas!

Thanks again
Vicky

 

"There is much pleasure to be gained from useless knowledge"
- Bertrand Russell, philosopher (1872-1970)

It's only worth doing as part as a considered tuning program. Unless you
know what you're doing, you'll probably make things worse. Also, it's not
worth spending time and money trying to squeeze more go out of a learner
bike. Dick Dastardly of this parish once tuned a CG125 up to 25bhp and got
the dyno ticket to prove it, but it blew up the next week. Concentrate on
passing your test, then buy something more powerful.

So it goes.

 

Yes, thank you Kurt. I was expecting a contribution from ginge. Has he,
you know, *met* someone or something?

 

Wot everyone else said. If you do something as simple as putting a
different carb on, there is a 1% chance that you will get a slight
improvement, and a 99% chance that you will bugger everything up and
it won't run properly until you put the original back on. Plus,
standard bikes are almost always worth more than anything home-
modified. From what you say, you sound as if you might be wanting to
trade it for something bigger in the next couple of years, so keeping
it standard is probably your best option. The difference in
performance (assuming you improve it rather than wreck it) will be
tiny in any case.

 

http://img.photobucket.com/albums/v170/Vks24/fingers2.gif?t=1191056398

 

Ooh - look mummy - Sooty and Sweep are naked.