15:1 fuel air ratio is considered best in most applications. Too lean runs hot, too rich fouls.
SOURCE: hard to start yz250 dirt bike 2001 4stroke
i used to own a yz426f and it had the exact problem... a fresh plug will fix your problem. change the plug and the bike will run great. also don't start the bike and shut it off , my bike would be fine if i started it and rode for a while getting to the proper heat range help save the plug. if my bike didn't start in one or two kicks it was usually the plug.
hope this helps
SOURCE: My FZR600 won't start. No mods, all stock. I got
it is possible that th eplugs might be fouled but it seems unlikely after only two weeks running-my fzr would foul plugs but it usually takes months not weeks-also the engine would start but run on2 or 3 cyls. I found using one heat range hotter than standard plugs helped,esp. around town you seem to have been fairly methodical on your troubleshooting-if you have fuel and spark the next thing to check is comp. -if the plugs are wet it is likely fuel not oil-when I first bought mine it had sat over winter and would not start -it turned out that the valve clearances had closed up enough that it was low on comp. when ridden frequently it was ok but as soon as the oil had drained off the cyl walls it would not start-squirting oil in the cyls. would get it started but I pulled the cams and set valves to solve problem-starts ok now but I don't use the choke-you could lift the cover and check your valve clearances -it would be a good idea on a bike that you just bought-don't give up -be methodical and check one thing at a time-when you get it going it will be worht it
SOURCE: Mixture screw on Carb
I believe it is near the bottom, around where the float bowl meets the carb body.. You need a straight small screwdriver (Short) facing upward.
SOURCE: carb puking gas
I had this same problem. What I discovered was the float needs adjusted on the carb. I set mine lower inthe bowl and it stopped the leaking. Reason for this happening is on hot days the fuel in the bowl will boil. This boiling action dumps in more fuel and the carb spits it out the air breather.
SOURCE: i have a sym jet
Lightly seat both screws then open each of them one and one half turns. This is the factory setting for Japanese bikes. Clean the air filter, install a new spark plug, I assume the Sym has a two stroke engine, mix the gas ans oil 32 to 1. That equals 4 ounces of two stroke engine oil per gallon of gas. NEVER use motor oil, only two stroke engine oil. Also, tighten all carb fittings such as mount bolts and clamps. Replace any rubber fittings if you see cracks. A cracked manifold will let air into the mixture which leans the mix and makes the idle rev upward.
Testimonial: "absolutly spot on"
If you look at a carburetor,
you will notice a rather large hole going from one side to the other.
This is called a Venturi. Air passes into the engine through this hole
(Venturi). As the velocity of the air entering the carb (and then the
engine) increases, it's pressure decreases, creating a low pressure or
vacuum in the venturi. This vacuum moves around in the venturi, as the
throttle is opened, and sucks gasoline through the different jets in the
carb. The gas then mixes with the air going through the venturi. The
way the jets are made
causes the fuel to vaporize as it goes into the venturi. Where the jets
are placed in the carb and where the jet's outlet is located in the
venturi, determines what part of the throttle opening that jet controls.
The idle jet system (comprised of pilot air jet, pilot fuel jet and
pilot fuel screw) controls from 0% to about 25% of the throttle opening.
The throttle valve controls 0% to 35% of the throttle opening. The
needle jet and jet needle control from 15% to 80% of the throttle
opening and the main jet controls 60% to 100%. This means that when you
open the throttle about one eighth of the way open, all of the gas/air
mixture going into your engine is controlled by the idle jet. As you can
see, the different jets over lap the operating range of each other.
That is, the jet needle starts to effect things before the effect of the
idle jet ends. This is something to remember when working on carbs...
everything is interconnected. Change one thing and it will effect other
things.
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