diaphragm fuel pump not working - KT100 2 cycle

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after assembling a very sorry Yamaha KT100 2 cycle kart engine - it is not pumping fuel. I was a little surprised that the line from the engine to the crankcase actually seems to be pushing air - I was expecting suction. is that correct?
 
yes a two stroke builds pressure in the crankcase, totally different design than a 4 stroke. the pulses will operate the external pump if you are fitted for one
 
When the piston goes DOWN, it pressurizes the crankcase - that's how the air fuel mix gets from the crankcase -> up through the transfer ports -> into the combustion chamber.

When the piston goes UP, it makes a vacuum in the crankcase.
That is how the air/fuel mix gets sucked through the carb.

Get it?
 
diaphragm pulse pumps are dirt cheap for an externally mounted one, should be able to track one down on ebay or amazon for under $20.
 
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