carb sizefor 44mm 65cc airsal

Brad William /

E50. Techno hunter pipe.

Anything from 14mm to 24mm depending on how you ride, where you want most torque.

Any rough calculations that apply?

Cfm, volumetric efficiency, bore/stroke, displacement, etc. There are calculators and spreadsheets for this. Is it reasonable to think that the engineers at, for instance airsal, have done most of the math for me in designing the intake port for (unmodified) use?

Hope my math is sound here. On this airsal the intake port is approx 270mm sq in the cylinder and approx 320mm sq at the manifold port. That puts the 314mm sq of a 20mm carb throat right in the midrange of these areas.

So smaller than 20mm more low end torque, higher than 20mm more potential gain at high rpm? 20mm carb, by these estimates, seems like a fair place to start.

How far off am I? (edited)

Re: carb sizefor 44mm 65cc airsal

Dirty30 Dillon /

Anything over 20mm will probably be wasted on that cylinder. I'd say a VM20 would be the maximum, a 17/17.5 PHBG/PHVA a good in between, and a SHA 15.15 a great budget option.

Re: carb sizefor 44mm 65cc airsal

yeah port dimensions aren't always the best for carb sizing, generally you want the biggest part of the intake to be at the port (on a piston port)

dillon is spot on, but i think a VM18 would also be a good choice on that setup.

Re: carb sizefor 44mm 65cc airsal

Ditch the tecno hunter if you are looking to see any increase in performance.

Re: carb sizefor 44mm 65cc airsal

Chloe Feldman /

I think you're overthinking it a hair but definitely somewhere on the right track.

I have a 19 phbg on my ZA50 / 44 airsal. It's a pretty god damn detuned kit in my eyes. Low-key kinda wish I copped something else. I feel like the 19mm is definitely more than enough carb and probably a 17mm ( or maybe even a little smaller ) would have been a bit more realistic for the cylinder.

I'd ditch the techno hunter for a better chamber unless you're really into the aesthetics etc..

Re: carb sizefor 44mm 65cc airsal

Brad William /

I think you're overthinking it a hair but definitely somewhere on the right track.

...I'm badly prone to that:)

The tecno hunter was an improvement on stock for me. Only 5-10 mph faster but much better midrange torque. I'll try it with the airsal jug and see what's what.

I'm always trying to keep this mopeddaling cheap and effective. It's part of the fun of it for me. When the modification wish list for this starts to exceed 600 dollars (cdi, stuffed crank, better clutch, better pipe, premium bearings, premium carb, new seat, better lights, etc) I start looking at used small motorcycles for not much beyond than that and thinking hmmm....

generally you want the biggest part of the intake to be at the port (on a piston port)

That's interesting. My rough calc of the 44mm airsal puts the intake port 15 percent smaller than the opening to the intake manifold flange. The port tapers outward. The square(ish) port (inside) at 270mm sq is equivalent to a 18.5 diameter circle.

While I'm here, Is the E50 "hi-torque" head ok with this airsal kit without any modifications except adjusting for squish? It appears as if the piston crown will be very close to the edge of the dome since the head bore is a few mm smaller than the bore of the airsal. With proper squish the piston would be dangerously close to this lip. I didn't really see any specific head recommended for this kit at treats. (edited)

Re: carb sizefor 44mm 65cc airsal

Tri-ped Dave O.D.B. /

Carb size has always been a subject on this forum that makes me howl laughing. I built a 55mph plus Tomos with a stock 14.12. (Witnessed by over 20 Boston folks on a weekly ride)

Most people reccommend a carb that is actually way too big and doesn't add performance, just sucks extra fuel. For a 44 kit a 17 is the absolute largest I would go. I would actually run a nice 15 Amal. Going too large makes tuning problematic, especially the idle, and buys you nada for extra performance. Tune it right and don't over-carb!

Re: carb sizefor 44mm 65cc airsal

Brad William /

I don't have a wealth of experience with small one cylinder bike engines. Mostly mopeds. But I did tinker with rebuilding a kx80 water cooled once. The ports were ENORMOUS, and the keihin feeding it was likewise ENORMOUS. Thing had gobs and gobs of low and high end torque. It was a beast really. And probably designed to be fully rebuilt every four races when stretched to it's limits.

Yes port size isn't a good determiner of carb sizing. But it would seem that some rough, and relative, relationship exists here.

Re: carb sizefor 44mm 65cc airsal

Brad William /

Seems like there is a very big range of sizing depending on use/needs.

The KX80 makes astonishing amounts of torque/hp/rpm out of 80ccs by water cooling it, opening up it's breathing passages to its practical limits (enormous ports and 28mm Keihin). But it's a thoroughbred meant for races. High maintenance, eats huge amounts of fuel, and dies young. At the other extreme is the tiny ported lowest hp rated e50 with 12mm bing and restriction plug on the airbox. Meant to sip gas, be quiet, and last a LOT longer between top end builds than the KX80.

I'm adding the 44mm airsal mostly for small improvement and good reliability. Hoping to slap a carb on that won't require much adjustment in jetting beyond the middle of it's intended range. That would be a good fit. (edited)

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