9.9 yamaha very hard to start and backfires when cold.......AOK hot

[Capt. John Deering]

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i use the 9.9 Yamaha 4 stroke as kicker on my 23 cc console. its a bear to start sometimes and will backfire fairly bad when cold. after it warms up it runs great.

i have:

--check fuel pump with vacuum gauge


-- disassemble and cleaned the carburetor, used compressed air too.

--checked electrostatic valve...ohms and movement.

--checked fuel filter

big motor has not problem, i have a 2 micron filter that is used for both motors.

any ideas

[rodbolt17]

fix the lean condition when its cold.
something is not right on the enrichment circuits.
ditch the 2 micron filter.
its way to restrictive.

[Capt. John Deering]

enrichment circuits? what do they consist of?

rodbolt, is the issue a carburetor problem only.

[rodbolt17]

sounds like it.
the electro thermal valve retracts as it cools.
once running stator voltage is applied and as the wax pellet inside heats up the needle extends and closes off the enrichment port.
either the needle isnt retracting or the port is clogged.
remove it, measure it cold, apply 12V with a set of jumper leads for a few minutes, neasure it again, let it cool for 20 min and measure it again.

[Capt. John Deering]

problem solved:

i learned a valuable lesson........i tore the carb apart twice used spray carb. cleaner and blew everything out with compressed air.

still hard to start and contineous backfiring.

this time the carb was disassembled and soaked for 2 days in carb cleaner.

blew it clean and re-assembled.

she purrs like a kitten.

lesson learned......you cannot properly clean a carb. unless its soaked in carb cleaner.

[rodbolt17]

dunno
I do 5 to 10 a week and I have not soaked one in probly 20 years.
just did 4 on an F50 yesterday.