Zundapp 1938 500cc running rich Amal carb issue

freefly103

freefly103

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A friend’s bike, built from a bucket of parts, running rich with an Amal pre mono bloc carb currently running rich with a 140 jet. He has 4 jets from 106 to 140.

We went out today and did a couple of tests at WOT. Bike runs well across the rec range. Fuel consumption is about double what it should be. Occasionally pukes black smoke from the pipes on acceleration. Plugs are black when pulled after WOT test. We raised the needle clip to the top to lower the needle. Will test at WOT again tomorrow.

Does any one have experience with this type of carb in a 500cc bike?

Appreciate any input.
 

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I am going to take a wild guess and start looking at the float, float needle and seat. The sudden pooping out of black smoke indicates an intermittent rich condition. The age of the carb and the condition of the float needle would be my first concern.
 
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