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I recently bought a 1986 Moto 4 250 for 200 bucks. It ran but it smoked so I figured a new set of pistons rings would help. I took it apart and replaced them and put all new gaskets. I can't get it to fire up now and I think it may be the timing. I don't hear the valves hitting the piston so I am sure it is close. I got it together and I thought it was timed but everytime I tried to crank it gas would shoot out the back of the carburetor. Does that mean the valves need to be adjusted? If so how do I do that? Also how do I time one of these? Please Help.
First make sure you got spark and compression. Also check to make sure the valves are adjusted right. As for the timing, I have not done it on a moto4 but it has a smaller version of the Warrior motor.. so I'll base everything off that. There should be a little round plastic cap on top of the flywheel cover (left side of the motor when sitting on the quad). Turn that cap off. Also take the large round cover off the same side of the motor and remove the sparkplug. Using a wrench or breaker-bar with a socket to turn the flywheel counter-clockwise until you see a T mark in the little hole on top. It should line up with an arrow or mark inside the hole. You will need to be at T (TDC) on the compression stroke. So open up the valve covers and see if you have some freeplay in the rocker arms. Both valves should be fully closed with some freeplay in the rockers. If the rockers feel tight and/or a value is open you will have to turn the flywheel one more time until T lines up again.. at that point the crank should be at the correct timing for TDC on compression. If the rockers feel tight at both TDC marks you will need to adjust your valves first. If your flywheel doesn't have any lables but just lines like this || then the TDC mark will always be the LAST mark when turning the flywheel counter-clockwise. Your cam sprocket should have a single line on it that will line up with a mark above it in the head when the crank is at TDC.
I always heard people in the forum talking about the T mark but I could never find but but now I have. Thanks Very much. If it is just a little bit off would it still crank because I was pretty close to it already.
Could he valves be bent from where I didn't have it timed before? When I tried to time it the first time I could hear the piston hitting the valve as it came around. I think that could be the problem because the carb sucks and pushes with the motion of the piston.