how to: cam timing

[ghost civic]

it seemed like my 86 yamaha 225dx was pushing fuel out the carb. like the piston would start coming back up to TDC before the intake valve was closed.
i figured out how to take the chain tensioner out, and remove the chain from the cam gear.
NOW....how to i get the valves to open in close at the right time? i know there is a TDC mark through a hole near the pull cord, but how do i know if its should be TDC on the exhuast stroke or the compression stroke? i need to know in order to set the cam gear right before i put the cam chain back on.

[atctim]

did you check your valve clearances before you messed with the timing? An un-adjusted valve or a hung valve would cause this same effect.

[ghost civic]

yes, i checked valve clearance 1st.
i only needed to make very minor adjustment to valve clearance.
still, there was hardly any suction on the air inlet of the carb. i dont have access to a vacume gage, but im pretty sure it wasnt enough suction to pull gas through the carb.

another question for you guys, how many times should the intake and exhaust valves open per 1 rotation of the cam gear?
i ask this because i notice on mine that the intake and exhaust valves open very close together, with about 40-45 degees seperation. seems close together. then again, iv never tried to work on any atc motor before.

[DixiePlowboy]

The TDC mark is the correct one for timing it up with the cam.

If you have the TDC mark on the bottom(crank), there should be a mark on the head to line up with the mark on the cam gear. I can't remember if it's up or down(I think up) since I've been working on Hondas alot lately.

With the crank marks lined up, your cam lobes should be facing (more or less) down. (Say at about 4-o'clock and 8-'o'clock or so)If you think you've lined up the cam gear marks and your lobes aren't down, you're 180-degrees off.

[ghost civic]

thank you. know i think i know what i was doing wrong. i think i had it off 180 degrees.

[DixiePlowboy]

another question for you guys, how many times should the intake and exhaust valves open per 1 rotation of the cam gear?
i ask this because i notice on mine that the intake and exhaust valves open very close together, with about 40-45 degees seperation. seems close together. then again, iv never tried to work on any atc motor before.

Each valve will open only once per revolution of the cam gear/cam. The seperation of the lobes looks close because it's supposed to be. At the end of the exhaust stroke, the intake stroke begins right after the exhaust valve closes. Your piston sees a closed off cylinder(while running) longer than it sees an open-valve cylinder(both valves included), therefore more of the cam's circumference is devoid of lobes.

Hope this helps......I'm not really a 4-stroke guy, but I work on them alot.:beer

[ghost civic]

Each valve will open only once per revolution of the cam gear/cam. The seperation of the lobes looks close because it's supposed to be. At the end of the exhaust stroke, the intake stroke begins right after the exhaust valve closes. your piston sees a closed off cylinder(while running) longer than it sees an open-valve cylinder.

the timing of the valves openning is close, but its the other way around...
the intake opens, then the exhaust opens soon after. the larger gap in timing is from the closing of the exhaust and the opening of the intake.
i dont see how it could be that far off. maybe i need to take a closer look at it. its dark now, will have to look at it tomorrow.

[DixiePlowboy]

If it's the correct cam for it....... Line up your marks and everything should be good to go.

[Yamada]

Where is Dirtcrasher???