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Performance Carburetor Options

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pyroian

Guest
I have been searching the posts for performance options, but so far I have not been able to get a straight answer on carburetors. What is the best carb for the powerking motor? I'm thinking the Mikuni 22mm available on ebay, pocketbike sites, etc., will be a good option. Anyone have any opinion yay or nay? Also if an expansion chamber is put onto the engine, will it have any effect on the carb choice?
 


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prism

Guest
Carb size

22 mm is way too big for a stock engine. The standard sized carb is a far better fit unless you do the following:
1) raise the exhaust and transfer ports, and 'drop' the intake port, while simultaneously widening and shaping the various ports to the maximum width (i.e. about 65% of the bore for the exhaust)
2) fit a properly dimensioned expansion chamber suited for the revs your engine will work best at (half again as high as stock, if not higher yet)
3) toss nearly all of the parts! (no, no joke. Stresses climb with the square of the rpm, hence 50% more rpm means more than double the loads on the internal parts, and the manufacturers didn't overbuild these engines.)

Once you have your new engine, then the following happens:
a) you lose most of your low-end torque - meaning, you need to pedal a lot more to start off - as well as any time the revs drop out of the engine's powerband.
b) your engine becomes a lot more cantankerous than it was before.
c) maintenance becomes a much bigger job - and no 'bodging'. If you do not do the work 'right', you will regret it when your engine seizes or scatters itself.
d) reliability falls off markedly.
e) fuel consumption goes up substantially - and better fuel, also. You'll want to make friends with an airplane driver so as to get some 100 octane avgas to mix with the best premium you can find - and no cheap oil, either. Only the best will serve (i.e. Bel-Ray H1R, Maxima Castor, Klotz Techniplate, or similar)
f) your 'normal' cruising speed will have the Gendarmes chasing you every time you ride, and the 'spine-tingling howl' of 8,000+ rpm will irritate everyone within half a mile who doesn't like to hear 'the sound of power'.

Hope this helps some.
 
A

Alaskavan

Guest
Just an opinion with no experience behind it. You might be able to find a carb that is more "tunable" in about the same size as the stock one (14mm?).
 
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pyroian

Guest
so the 22mm is out, stock is 14mm? I just need something more "tunable" for sure. any feedback on a pipe for it?
 
5

5-7HEAVEN

Guest
:cool:same here with no experience.

a popular model that 40cc-49cc pocket bike engines use is the DELLORTO 14/14mm carb. Its REPLICA is on sale at davesmotors for $25, or $35 with filter.

i've thought about buying 2 of them for my twin-engine project.

Myron
 
F

fetor56

Guest
:cool:same here with no experience.

a popular model that 40cc-49cc pocket bike engines use is the DELLORTO 14/14mm carb. Its REPLICA is on sale at davesmotors for $25, or $35 with filter.

i've thought about buying 2 of them for my twin-engine project.

Myron
I don't know how long this sale lasts but if u go ahead and try the Dellorto 14/14 Replica can u please let us know...i'm sure plenty of ppl would be interested.
 
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pyroian

Guest
cool I will give that carb a try but first i have to deal with a broken rear mount :(
anybody have any idea why these pocket bike 50cc motors can use 22mm carbs? advertised on ebay as compatible...why not for the powerking? its all the same right?
 
A

Alaskavan

Guest
Are you looking at a pocket bike that says it has a powerking engine? If not, chances are that it is not.
 
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prism

Guest
carb size

The size of the carburetor is related to the volume of air that flows through it during a given time period, which is why a larger engine needs a larger carburetor, given all other conditions (rpm, volumetric efficiency) remain the same.

Let me guess about that pocket bike engine you were refering to:
1) it isn't a stock engine, even for *pocket bikes*.
2) the engine itself has the internal parts, porting, ignition timing, and exhaust to turn upwards of seven to nine thousand rpm. (Vs the usual 4500 to 5000 rpm of the 'happy time' engines)
3) it most likely has a reed valve. (permits use of a larger carburetor, due to assymetrical (sp?) intake timing.) 'Happy time' engines tend to be piston port, which means a larger carb will cause 'loading up' when opened wide at low revs.
4) Gearing, clutch, etc work around the lack of bottom end torque, i.e. the clutch doesn't engage abruptly, but slips some to permit the engine to climb into its power band - like some kart clutches do. I suspect 'fanning' a 'happy time' clutch is a sure quick way to ruin it.

I've worked on my share of two-stroke engines over the years, welded an expansion chamber or two, jetting, timing, overhauls, ports, etc. Two books you might want, one by Gordon Jennings (out of print) and A. Graham Bell. This last is available on the net, though the downloaded version is sufficiently poor that purchase is wise if you plan on really using it.

Hope this helps some.
 
5

5-7HEAVEN

Guest
:cool:Well, i bought the DELLORTO replica, a copy of the carb on a Polini 40cc air-cooled Italian pocket bike engine.

then i bought a 40cc Polini engine with a genuine DELLORTO 14/14 carb on it.

Prism, my $99 pocket bike engine originated as an OEM Ebay purchase. Both are reed-inducted engines, so both should breathe well enough, maybe 9500rpm or more.

i also installed an offset timing key and ordered a billet "X-CAN" for the pb49. the can's flange was too wide, even tho i ordered for the correct 49cc engine.

pocket bikes' tuned pipes are way too long for my cruiser bike, so i'm ordering an expansion chamber for a goped scooter and hope it fits.

FWIW, ya can't just enlarge carb size alone. other mods have to be made to take advantage of the better breathing.

i guess i'll also have to lower my gearing.

Myron
 
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