S

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5

Brian, two 12mm carbs equals one 15mm carb.

The area of a 12mm surface = pi X radius(r) squared = 3.1416 X (6mm X 6mm) = 3.1416 X 36mm squared = 113.0976mm squared. Two carbs = 2 X 113.0976mm squared = 226.1952 mm squared.

The square root of 226.1952mm squared = 15.0397mm or one 15mm carb.

This is equivalent to saying two 12" pizzas are not equal in size to one giant 24" pizza.

HOWEVER, if each carb is rated at 120cfm(cubic feet/minute), then two carbs WOULD rate at 240cfm.

Myron

The area of a 12mm surface = pi X radius(r) squared = 3.1416 X (6mm X 6mm) = 3.1416 X 36mm squared = 113.0976mm squared. Two carbs = 2 X 113.0976mm squared = 226.1952 mm squared.

The square root of 226.1952mm squared = 15.0397mm or one 15mm carb.

This is equivalent to saying two 12" pizzas are not equal in size to one giant 24" pizza.

HOWEVER, if each carb is rated at 120cfm(cubic feet/minute), then two carbs WOULD rate at 240cfm.

Myron

Last edited by a moderator:

J

You have to divide the 226.1952 figure by pi THEN take the square root THEN multiply by two to get the equivalent diameter.

So the actual equivalent of two 12mm carbs is one 17mm carb in terms of cross sectional area.

I agree that the flow capacity will be roughly doubled.

Bryan, the Chinese two strokes actually depend on a slightly restrictive intake tract/carb to improve performance. Because of the huge overlap in valve timing on a 2 stroke, the piston forces gasses out of both the exhaust and intake on the upstroke. A slightly restrictive intake tract/carb provides some resistance to reverse flow and, therefore, keeps more air moving in the proper direction through the engine. Reed valves can virtually eliminate the undesirable reverse flow but at the cost of adding another restriction to flow in the intake tract.

Two stroke tuning is completely different from four stroke tuning so the things that work on a chevy are not directly transferable to our little Happy Time engines. But hey, give it a try! Experimentation is almost always a learning experience. Even when the experiment is a failure we at least learn what won't work and if we manage to sort out why it failed we have learned something.

A

I love the idea of dual carbs....but the one concern I would have is along the lines of intake flow capacity.....by adding 2 carbs we would need to ensure that the intake manifold is not too restrictive and can flow the volume of 2 carbs as they both come fully open....this would suggest an intake flow roughly double stock?...If so I am wondering how this would be accomplished given the relatively small intake area in the stock cylinder (maybe mild porting....I noticed that the port opening inside the cylinder is narrower than the opening where the intake manifold bolts to the cylinder jug).....as far as the need for intake restriction to help prevent intake reversion through the carb , I believe that is where the boost bottle would come in handy. Who knows?....maybe it would give some benefit by just splitting the intake manifold and adding another carb....definitely try it and let us know what you find...I can hardly wait.

Andrew

5

You are correct.

Myron

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C

All th' restrictions is creating TORQUE....................thusly, causing VIBRATION!!!!!!

I have always found that poor quality flywheels that aren't properly balanced, and engines that are not mounted securely cause excess vibration..not torque.

Torque is what gets you up and moving. Trust me, you want torque...it's a good thing

S

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J

Torque (in lb/ft) X RPM

5250

If you're pedaling to help overcome inertia you're using energy from that ham sandwich that you ate to help make up for lack of torque from your engine.

Good torque at low RPM with a Happy Time or any engine working in a drive train that has only one gear ratio is a really good thing.

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