Carburettor Angle question...

[jji7skyline]

My motorised bicycle has a 70cc engine with everything stock, NT carb and 44T sprocket. I'm reaching a top speed of 40kph on a good, warm day.

I've read product reviews of the kit doing over 50kph.

I'm currently running approx 15:1 to 20:1 fuel (for break-in, but my next can of fuel will be 40:1), and my bicycle has been ridden for about 30 min everyday for about a month.

I get really good low-end torque, and I am blown away by its hill-climbing ability, but I want a faster top speed, specifically, around 50kph.

The carburettor is actually mounted at an angle, so if you look with your eye on the rear tyre, the carb is tilted around 20° to the right. I heard that these carbs work best when perfectly level because of the way they induce fuel through airflow, could this be affecting my top speed?

 

[GearNut]

I with that angle,no. However a new engine is slow when compared to a properly broken in engine.
Wait until you have 800km on the engine before you judge it's top speed.

 

[jji7skyline]

Ok, thanks. The carb was mounted that way because of a smaller frame size

 

[Nashville Kat]

If it's tilting back that way- you might get better results with a short billet intake

You'd defintely see better speeds with a 36 sprocket, but I don't know whjat kind of hills you're dealing with, or how much you weigh. And you'd get a better cruising speed with less RPMs- I went to 36 long ago, and then even 34 here in flat Florida- But still have a 39 on my 50CC-

The other big speed enhancer could be the tires- if you'd be comfortable on something more narrow- you definitely get a better roll with narrow , lighter tires

26" tires go down to 1.25- a little hard to find- but I'd recommend 1.5-
the smaller tires of course cost more and wear just a bit faster- 1.5 is a nice fast rolling size that still has rubber for potholes

 

[jji7skyline]

Sorry for the newb question: what is a short billet intake? I've been thinking of getting some sort of intake mod, but haven't been sure which.

I live at close to sea level, weigh about 150lb/68kg, and I'm tackling some hills that are impossible to climb on a mountain bike except on lowest gear, on grass.

I've tried to cut down on rolling resistance by pumping my tyres up to almost 60psi (they're rated for 50), and I'd rather not spend money on tyres that wear even faster (these ones are only a month old and already almost worn).

Do you know what kind of RPMs my engine might be getting with 40kph on a 44T?