MOPED ARMY

the alexander graham bell book reccomends a 26mm carb for 50cc applications

charts aside in reality i think you'd have to get to like a 30mm carb to get that effect.

I'd really like to see a 24 flatslide on a heavily ported polini. I am curious to see if it would work.

what this is saying is, if the carburetor bore is too big, than no matter how big a jet you put in there, since the air stream is insufficiently fast at WOT, an insufficient amount of fuel will be drawn out of it at WOT. you could not even have a jet - it'll still be lean.

I always thought my 19mm dellorto was better on my 65 metra than others running a 21.

I am still curious on the polini though. I think the mikuni is a much more advanced carb and if tuned correctly could produced enough power for you guys to blow your polinis up even quicker. Taking it to an rpm range it hasnt seen before, but this is a total guess.

The mikuni flatslide is very smooth and responsive.

b4 a bunch of ppl decide any 15mm carb is better than a 19mm. after seeing that chart I want to make somethings clear.

It should be noted the chart recognizes the carbs despite being different sizes to essentially all be of the same design. So if are deciding between a 15 SHA and a 19 phbg the bore size is a minimal upgrade compared to the tunability and proper fuel metering during all throttle ranges and rpms the 19phbg provides.

While one might think the 19 PHBG too large it will make up for this in how it delivers the mix. And ultimately be much more responsive, produce more power, and have better low end (torque) than the SHA 15mm.

And for the record I have never seen a 65 metra that did not like and perform supremely better with a 19phbg over an 15mm carb, bing included.

Tommy I really want to try a 24 flat slide one day on a pumped up polini as well. I can only envision good things.

just a thought... don't bigger carbs get better gas mileage?

No. bigger carb = more air + more gas = less gas mileage

The intake tract works as an entire system to deliver air to the cylinder. Y'see the interesting thing about intakes, is that no matter what you do, you can never ever get more than 14.7 psi of pressure differential across the entire intake. The carb is designed for a certain flow rate based on that pressure drop. If you streamline the intake tract, it has the effect of increasing that flowrate and therefore require a carb capable of more flow. If your engine is ported with 4 petal reeds, it is flowing way more than the stock crappy 2 petal that the 15 bing is meant for. At that point, you have enough flow that you will keep a steady diff. p across that bigger carb. The flow will be directly related to your horsepower. If you can rev a polini to 16 grand with a huge 4 petal reed, and make 12 or 14 horsepower out of it, you better account for that on the chart.

I dont care how skinny you are, you cant go 60 plus miles per hour on anything with less than 7 or 8 horsepower. You guys that are pushing 65 on your metrakits and polini's have to be making more than 8 horse. My calculations, and testing, have shown 60 mph on a scale model pinto requres 8.6 horsepower to overcome estimated losses.

Mikuni+Polini=awesome. I really want to try it. When I phase out my current polini, I'll try it. Worst case I blow it up.

too many numbers ahhhhhhhhh. damn u graham and ur technical equations. and scale moped models lolz.

gas mileage, i have no idea.

thanks - too bad it' out of stock though

they say the 50v engine from a 76 mobylette puts out 1.6BHP, and goes 30mph with a lightweight rider. so in order to double that, you must multiply the horsepower by at least 6? theres an exponential decline for you.