Performance Carburetor Options

Discussion in 'Performance Mods' started by pyroian, Oct 25, 2007.

  1. pyroian

    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?

  2. prism

    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.
  3. Alaskavan

    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?).
  4. pyroian

    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

    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.

  6. fetor56

    fetor56 Guest

    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.
  7. pyroian

    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?
  8. Alaskavan

    Alaskavan Guest

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

    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.
  10. 5-7HEAVEN

    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.

    Last edited by a moderator: Nov 3, 2007
  11. prism

    prism Guest

    Carb size

    The 14 mm carb sounds a *lot* more workable for a 'happy time' engine (ref. to a 22 mm. That size generally goes on something - street-ridden - between 90 and 125 cc)
    examples: Yamaha 60 cc two-strokes (early 70's) usually ran 16 mm carbs. The two I recall either used reed or (in the case of the one I worked on) rotary valve induction. Both turned 6000+ rpm. Case in point: the rotary valve one had a wider powerband and pulled surprisingly ***hard***. (Take that for a hint, inscrutable oriental happy time manufacturers!)

    The chief advantages with the del'orto (spelling?) are 1) higher precision overall. This means longer life (parts don't rattle -> wear out) and more precise mixture control. 2) You can *get* jets, needles, throttle slides, etc, unlike the 'factory' carb. With those things, you'd best have a lathe, mill, and a *good* assortment of reamers, drills, brain lubricants (?) and related things.

    Hope this is of help.
  12. 5-7HEAVEN

    5-7HEAVEN Guest has a 4-petal reed upgrade for the DELLORTO carb on my pocket bike engine for $95. It's supposed to help the carb flow better, and is an improvement over the stock 2-petal reed induction.

    I think I'll get the 4-petals.

  13. ibdennyak

    ibdennyak Guest

    brain lubricants (?)

    good one :lol:, I could use some of that
  14. pyroian

    pyroian Guest

    anybody know anything about mounting a reed induction system on the happy time engine? I saw a deal on ebay
    that i thought i could make work, however it looks like you might need two of the oval looking piece (one for each side) in order to make it work, which means that unless the seller can hook it up, the only option is to buy two in order to make one. the upside of this is that spare parts will be abundant...however, the seller will not give me the dimensions of the holes in the intake manifold so I cannot check to see if it will fit the cylinder or say nothing of the space required to do so. A reed system would be pretty badass though, anybody? and 5-7, you are using a pocket bike engine on your bike? do you have pics?
    Reeds aside, the carb in question should provide much more adjustability, which will definitely come in handy once I port and polish the cylinder and intake this weekend.
  15. prism

    prism Guest

    reed valve

    Fitting a reed valve to an otherwise unmodified engine would *reduce* power, not increase it. Why?
    1) A reed valve permits 'ready' flow in one direction, and little or no flow in the other. By 'ready', I mean with little restriction (vs. no restriction in an unobstructed intake tract).
    The intake timing of a happy time engine is sufficiently 'short' that backflow, save at the very lowest RPM, isn't going to be an issue - unless, of course, your porting radically increases that timing event. (necc. for higher RPM operation)
    2) use of a reed valve (on an otherwise piston-ported engine) is associated with other efforts to 'increase power' (higher up the rev scale, as a rule) - longer intake, exhaust, and transfer events, AND added ports (in some cases.)
    Use of a reed valve permits a very useful type of boost port, one which comes straight from the back side of the reed cage. This type of porting uses the 'suck' action of a properly tuned expansion chamber to improve scavenging and breathing.

    Now for a 'dumb' question: How much metal is present at the intake side of the cylinder wall above the intake port? The reason I ask is that adding one or more small 'finger ports' fed from holes drilled in the piston would help power and longevity - power, in that the lower back side of the cylinder would receive scavenging flow, and longevity, in that the wrist pin (bushing) would get fresh oil-rich mixture on a regular basis.

    Hope this is of help.
  16. pyroian

    pyroian Guest

    I have no idea how much metal is there I haven't had the thing apart yet. I've only had it running for about 3 weeks. That is interesting that a reed valve doesn't do much for these engines. I just assumed from my experience with dirtbikes that it could only help, and when I was first running the engine I was getting some gas back through the carb into the air filter. That is what made me think of reeds, but then I ziptied my fuel line at the tank and carb and the "spitback" stopped. So you are suggesting that additional ports can be drilled into the cylinder wall? That is crazy! I wouldn't even know the first place to start on that. Can you explain that concept in more detail?
    So no go for the reed valve...Cool that will save me money!
  17. 5-7HEAVEN

    5-7HEAVEN Guest

  18. sunofjustice

    sunofjustice Guest

    Th' 14mm sha dellorto knock off carb works....OK......I installed one on my 47cc pocketbike schwinn spoiler.( #90 jet worked best) But, I prefer th' (modified) stock pocketbike carb. (reamed jet with medium-sized safety pin) It felt more gutsy.:cool: Th' 14mm sounded and looked cool.........but its NOT tuneable!:shock: (save for jetting) It IS a good basic carb for pocketbike racers that dont want to tear their bikes apart (between races) just to tune it.:confused: I will say this.....a real dellorto 16mm phbg carb would probably work best on a fairly stock "happy time" engine. This carb will provide ample tuneability.......and be ALOT more precise. (throttle response!)
  19. prism

    prism Guest

    Carbs - and ***carbs***

    I was looking up dell'orto carbs yesterday (I think it was yesterday) and learned that some of them are a good deal more tuneable than others. If I recall correctly, that 'knockoff' carb is a copy of one of the less-tunable variety, one where only the main jet is readily changeable. There's another 'type' with more letters which has replaceable needles, slides, main jets, pilot jets, etc.

    Once I learned that, I thought to look up mikunis. I knew the sixteen millimeters were being made currently (some smaller atvs use them) but when I found a place selling them, I nearly choked at the price!

    100$! (ouch!)

    Odd, though - an eighteen mm example is only seventy, and based on what someone (don't recall who, beyond they documented it on the list somewhere) said, it might be possible to jet that size so as to run *decent*. (he managed with a 20mm - oh, he said the engines were coming apart in a hurry, and *Dax* was speaking of his modifications causing them to do so - or so I recall.)

    Hope this is of help.

    I still suspect a sixteen (or slightly smaller) will give best low-end performance. Had we more than one 'gear', I'd argue for fitting the 18mm.
  20. sunofjustice

    sunofjustice Guest

    Prism, Ill be frank....I have used a 20mmcarb on my 70cc.....and it works! The ONLY problems I had from experience are from trial and error: 1st engine died six months later AFTER using 32:1 oil/fuel ratio suggested from other moto I broke it in using SYNTHETIC which was reccomended in the instructions! 2nd motor died ( actually the bushing worn out) from running in 20 below temps and not adding ADDITIONAL oil to the standard 5oz after breakin . 3rd engine went past 500 miles....... but blew gasket and oil seal from using TOO MUCH OIL and running it wide open for miles on end. (Hey, that "does 35-40 mph" sales pitch STILL lingers in my head) The 4th engine went WAY past 500 died when the upper roller bearing fell apart...and grabbed the piston at idle(???). The fifth engine was a stocker with VERY LITTLE mods.....had 7oz oil in it .....ran slow as **** and wtf .....the roller bearing died and wedged bearing pieces about the motor. What dax mentioned about modifications was ......PORTING...SHAVING HEADS....CHANGING PISTONS. And dont try to play all innocent like........virtually everyone on this site WANTS BETTER PERFORMANCE and HAS MODIFIED SOMETHING. Youre STILL suggesting a LARGER carb yourself.