Question:
Dear Motorhead,
I have a 1990 Yamaha Champ. Previous owner rebuilt the carb and it runs good when hot, but not cold.
I put a new carburetor on and it starts good but seems like the choke doesn’t work correctly (doesn’t rev up and run on choke like other 4 wheelers)
I also won’t idle cold very well have to feather the gas. don’t know carb
settings got any ideas. ps smokes a little, rings or valve guides.
keith harvey
Reply:
Thanks for your email!
You have exceeded my historical knowledge of ATV’s with your Q. However,I will offer some thoughts.
First, I suspect this engine is using a butterfly choke which are notorious for hard cold starts and poor idle.
Essentially the butterfly blocks all but a slight amount of airflow while allowing the carb mainjet to respond to the increased vacuum of the piston sucking against a brick wall and looking for something to eat.
Essentially, the mainjet “floods” the engine in a crude way and the motor eventually fires. The problem is there is little atomization of the fuel – it just pours into the mill, washes down the cylinder walls and creates smoke.
If you had an enricher circuit style choke the fuel is drawn into the engine in a much more orderly manner and as long as you do not move the throttle flipper, fuel is atomized and sprayed into the intake resulting in a quick firing of the mill. When you shut off the enricher idle drops and when it’s on idle increases.
Without knowing for sure what you’ve got I would say steady as she goes. If it runs warm, you’re at least running – right?
Thanks,
Motorhead mark
