MikeJ
Member
Hi All -
I have run my 79cc engine for just under 10 hours. It was simply underpowered for this altitude in Albuquerque (5500 feet to 7000 feet above sea level). The engine is running much too rich. The spark plug and exhaust pipe have a very heavy layer of plain black soot on both. The carb is starving for air and drowning in fuel.
I have since swapped out the old exhaust system (too restrictive and too long) to some shorter length and bigger diameter. The air filter is less restrictive now as well. Next is the carburetor; I am looking for ways to make it better. (Governor is gone, magneto pickup has been re-gapped, spark plug has been re-gapped; starts better than before.)
Attached should be photos of the carb when partially disassembled. The bottom screw holds the fuel sediment bowl to the center post. The screw out the side of the sediment bowl can be opened to drain water and old fuel.
Just below the plastic float on the side of the center post is what appears to be the main jet of brass (someone correct me if I am wrong). It restricts fuel flow going up into the venturi throat. I measured the main jet opening to be .025 inch (equals .635 mm) using a wire of equal size and a micrometer. This is from the factory; probably optimal for near sea-level air density.
If this engine is a Honda clone, would Honda have smaller-opening main jets for their 50cc engine that would fit into this engine? I looked at multiple Honda parts web pages and have not seen anything smaller than twice this jet opening.
I have read of soldering closed these main jets and then drilling out with wire drills that some of us have a hard time seeing. (Under-.025 inch drill is pretty small!) But if this is my only option, I will keep what I have and live with the overly-rich condition (at least for a while).
I realize this is a very specialized question, but if any experts have anything to say, I'd like to hear from you!
MikeJ
I have run my 79cc engine for just under 10 hours. It was simply underpowered for this altitude in Albuquerque (5500 feet to 7000 feet above sea level). The engine is running much too rich. The spark plug and exhaust pipe have a very heavy layer of plain black soot on both. The carb is starving for air and drowning in fuel.
I have since swapped out the old exhaust system (too restrictive and too long) to some shorter length and bigger diameter. The air filter is less restrictive now as well. Next is the carburetor; I am looking for ways to make it better. (Governor is gone, magneto pickup has been re-gapped, spark plug has been re-gapped; starts better than before.)
Attached should be photos of the carb when partially disassembled. The bottom screw holds the fuel sediment bowl to the center post. The screw out the side of the sediment bowl can be opened to drain water and old fuel.
Just below the plastic float on the side of the center post is what appears to be the main jet of brass (someone correct me if I am wrong). It restricts fuel flow going up into the venturi throat. I measured the main jet opening to be .025 inch (equals .635 mm) using a wire of equal size and a micrometer. This is from the factory; probably optimal for near sea-level air density.
If this engine is a Honda clone, would Honda have smaller-opening main jets for their 50cc engine that would fit into this engine? I looked at multiple Honda parts web pages and have not seen anything smaller than twice this jet opening.
I have read of soldering closed these main jets and then drilling out with wire drills that some of us have a hard time seeing. (Under-.025 inch drill is pretty small!) But if this is my only option, I will keep what I have and live with the overly-rich condition (at least for a while).
I realize this is a very specialized question, but if any experts have anything to say, I'd like to hear from you!
MikeJ
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