TOPIC:

The bike has good compression, I cleaned the carbs recently and have good spark. but the bike won't start even when removing the spark plugs and putting a bit of gas directly in the engine. I tried to do a rolling start too, no go. The gas is a little on the old side but I'm surprised that I can't get it to fire at all. (I'm changing out the gas tomorrow) any ideas would be appreciated

Try using some starter fluid

Have you checked valve adjustment? Have you load tested the battery? Are the vacuum ports plugged or hooked up to what they operate? Do the carbs seem to seal completely to the carb holders? Are the carb holders well sealed to the head? Are you absolutely positive that the pilot circuits in the carbs are spotlessly clean? Are the orings in the nylon plugs that go over the pilot jet in pristine shape?

the battery has plenty of pull. vacuum ports are all clean. everything is nice and sealed. I got all new Jets and new o rings. Not really sure how to check the valve adjustments. I just put the carbs back together exactly how they were before.

Also when I set the petcock to prime, gas comes out the overflow tubes on both carbs. So fuel is getting to the carbs

Cbguy wrote: Also when I set the petcock to prime, gas comes out the overflow tubes on both carbs. So fuel is getting to the carbs

Sounds like float levels need to be adjusted and / or float needle valve and seat need checked.

Do you have a timing light to check the timing? Good spark won't do much if it fires at the wrong time.

If you rebuilt the advancer unit (or someone else did) it's possible to rebuild it such that the timing is 180 degrees out. Then the spark will be at the exact wrong time.

If the advancer looks all clean and lubed, then I would check the timing.

When the F mark lines up with the pointer, the point of the rotor should be pointing at the center of the pickup (or very close to it).

Cbguy wrote: the battery has plenty of pull.

That is not what I mean. The battery can have enough power to turn the starter, but not enough extra to fire the ignition. If the voltage drops below about 10.5 volts when the starter is used, the battery is too weak to also power the ignition.

vacuum ports are all clean. everything is nice and sealed.

It is good that they are clean. One should have a hose on it connecting to the fuel petcock. The other one should be capped.

I got all new Jets and new o rings. Not really sure how to check the valve adjustments. I just put the carbs back together exactly how they were before.

They are not part of the carbs. The factory service manual explains the procedure. Unless they are so out of adjustment that a valve in each cylinder is not closing, it should at least start, but this will need tending to soon.
As noted above, if fuel is running out of the carbs, the float valves are not sealing. Another possibility is if those carbs have internal overflow tubes in the bottom of the float bowls, they could be cracked, broken or missing. The carbs should not leak no matter what the petcock is doing.

I haven't had much of any time to work on the bike as of late.

I think it is a timing issue but can't find that "f" mark. If anyone could point me where to look I'd appreciate it

Did you have a breaker point or a pickup (electronic) ignition?

Cbguy wrote: I haven't had much of any time to work on the bike as of late.

I think it is a timing issue but can't find that "f" mark. If anyone could point me where to look I'd appreciate it

It's on the timing advance unit behind the small circular cover on the main right-side (clutch) cover. The timing advance is the small disk that spins, in the very back of the timing compartment. If yours is an '81 it *should* have electronic pickup ignition, not points (unless someone changed that...).

With electronic ignition it's very easy to see the timing advancer because the pickup unit is much smaller than the points plate. The rotating part in back is the advance, and the stationary part in front is the pickup. Check around the perimeter of the timing advance for the marks; there should be one double tick mark, one F mark, and one T mark (in order going clockwise around the advance). If you don't see any marks, remove the spark plugs to remove compression from the engine, then using the inner 17mm nut turn the engine *counter*clockwise until you can see them.

With a timing light and the engine at idle (below 1400 RPM), the F mark should perfectly line up with the reference mark on the case (right below the top screw on the pickup).