Bigger carb?

[felixx]

So I run a Fa50 and just put an expansion chamber on her
Im wondering
1) Would a larger (say 14mm) carb help her go faster, or 2 smaller (eg chainsaw) carbs be better?
2) I know porting is a given, but how many gains could I expect?
3) How much should I skim the head?

Target is 65km/h

[Akzle]

slug the carb you have. That will be about optimum. Sprocket the bitch.
Port n polish... Thats, liek, 500 hache pees.

[gammaguy]

bigger is better

so its a 40mm carb off a TZ race bike

a set of expansion chambers off an ex barry sheene RG500(ultimate cred there)

a 17 rear with a 180/55 rear tyre,you will need the grip trust me,when you open up that bitch

oh and a set of 320mm dinner plate disks off an 1198 or similar(slotted and floating,naturally)

and while your at it go the whole hog and fit a twin spark setup cos you gonna need those plugs to be firing like a machine gun

should be good for at least.....oh.....63km/h

let me know how that one goes:brick:

[felixx]

something about fantasizing about rimming goats:

gummagay;
Its a valid question? Would a bigger carb make a difference
I guess you are too small minded to realise that some people
1) are still learning
2) aren't into big bikes
3)I was asking about carbs, not tyres, brakes and twin spark things

Akzle, what do you mean by slug the carb?

[fridayflash]

i wouldnt go for a bigger carb until more juice is needed...are those things piston port or rotary intake?

[unstuck]

if you want more power and better acceleration, i suggest you:
port it, mill the head a hair, bore it out "one over", bore out the carb, rejet it, polish the intake manifold/reed block, slap a boost bottle on it, run higher octan fuel in it and find a chambered pipe to graft onto it.

From here......http://www.mopedarmy.com/forums/read.php?7,1874647,1874659#msg-1874659

[felixx]

fridayflash It has a reedblock

Unstuck, thanks mate, I plan to plane a bit off the head, boring out the carb looks like a big job. Boring out the piston, I was thinking of that, it will give me an exra cc or 2 too!

Do boost bottles really make a difference?

[pete-blen]

Do boost bottles really make a difference?

yes...
They work mainly at lower revs... By reduceing the stop/start air flow though the carb...

Exspantion chambers are not easy to get right...
A very basic over veiw of what each section dose...
Header pipe length - detemands the rpm range it works in..
First cone - amount of vacume it pulls..
Body - how long the vacume remains for.
Rear cone - size / speed of the returniing pressure wave..
Stinger pipe/rear pipe Dia , length - how much pressure is held between ex cycles...
They all have to be dead right... Are linked to how meany
milli secs the exhaust port is open for at the rpm range you want the pipe
to work in... Port area...

if you go back to pre power valve bikes... you will notice the chambers were
longer & skinnyer than the bikes of 2day.. the diffrent RPM range the pipes are
tuned for since the power valve has come in to being...

[felixx]

Hi Pete
I will look at making a boost bottle soon
Just looking for a new fuel tap at the moment.

I also have an expansion chamber built for my FA50, it added 7km/h to the bike (16.67% increase)

I was thinking that now the outlet side is going well I would focus on the inlet side

[Akzle]

Akzle, what do you mean by slug the carb?
:

bore out the carb, rejet it,]

. .

[F5 Dave]

without a doubt one of the biggest restrictions you can make is to have the jetting wrong. Can make a strong engine sluggish or at worst lean & seize. I'm uncertain about autoclutch bikes as you can screw up the gearing by changing the revs peak power is produced. Your increase was as likely as much by removing a 20yr old clogged scooter muffler from the equation.

Big CC will always help, but there will be a limit on metal available. I run a 28mm on my race RG50, but I have 6 gears to play with & another league of revs & power, so yes there is scope a bigger carb will help as stock will have had fuel ecc in mind, but you'll have to take it through the whole inlet to help.

[felixx]

without a doubt one of the biggest restrictions you can make is to have the jetting wrong. Can make a strong engine sluggish or at worst lean & seize. I'm uncertain about autoclutch bikes as you can screw up the gearing by changing the revs peak power is produced. Your increase was as likely as much by removing a 20yr old clogged scooter muffler from the equation.

Big CC will always help, but there will be a limit on metal available. I run a 28mm on my race RG50, but I have 6 gears to play with & another league of revs & power, so yes there is scope a bigger carb will help as stock will have had fuel ecc in mind, but you'll have to take it through the whole inlet to help.


Thanks Dave,
that increase in speed was after the old exhaust had been soaked in a caustic hot bath for 24 hours

28mm thats a big carb, I was thinking 14mm

[F5 Dave]

Yeah no way the FA is in need of a 28, but it was a for example. And maybe 'mine is bigger than yours' 50cc talk. Intimidated?:innocent:

[felixx]

mate when you said yours had gears I felt squeamish

[gammaguy]

This thread takes extracting the michael to a whole new level

[the oldstuff]

Don't add a PCV

Weight reduction may be your biggest gain, especially gyroscopic (if that's what you are after)

[iranana]

Hi Pete
I will look at making a boost bottle soon


seriously, don't bother. on a machine as small (slow) as this, you'll hardly notice. i don't think they even have gears, do they? not to mention that the science of boost bottles is almost as complicated as chambers. as far as i understand, boost bottles only really help in race situations in that they increase torque and hp slightly before and after the powerband, so you can run corners is certain gears without falling out of power so abruptly. or something. i don't really understand how they work. you've also got to change your jetting if you install one. if anything, putting on some random chamber and boost bottle off eBay will make it run crappier, not to mention a chamber will probably remove any torque you have in the low end (if there was any to begin with)... my advice... keep it stock, imo you're wasting money for very little gain, if any.