Not turning over

1981 Kz250, the battery holds some charge, but this test was done with a car battery with a full charge. Even after a good charge, battery won't hold enough juice to turn-over the starter.

The starter motor will fire-away, sounds like it wants to start (turning over), but never quite catches-on. My first step will be acarb cleaning (not sure of the last time that happened), then...any other obvious steps I should be taking/things I should be looking for.

Opinions? Questions?

Choke on, key on, petcock on, kill switch in "RUN", clutch lever pulled in, and do NOT touch the throttle when trying to start it. Be sure not to jump it from a vehicle that is running or from a battery charger or you can fry the electrics. Ed

points! (if you still have them?)

If you're saying the battery does not hold enough power to rotate the crankshaft, then take a jumper cable and put 12 volts directly to the stud on the starter. If it still won't turn over, take the starter apart and clean it out.

If you're saying the engine spins over but don't fire, then do the things mentioned above.

Does that bike have a kickstarter?

It'll turn-over, but won't fire-up. So, I'm assuming I don't have to clean-out the starter. BUT, if I wanted to (at around 25K mi), how would I do so?

At 650ed - when trying to start it the other day, I was doing all you suggested, but I was twisting the throttle - why is that a bad idea? Also, the vehicle I was jumping from was definitely not running - I'm aware of how I could fry my electrics starting from a running vehicle.

The '81 250 has an electronic ignition, so you don't have points to worry about. Check for spark first, make sure the ignition is working. If you have spark then check the carb. Start by opening the drain screw in bowl to check for gas from the tank, then you know its time to clean the carb.

The CV type carb on that motor is VERY cold blooded and set up very lean from the factory. it has to be perfectly clean and there can be NO leaks around the manifold or the air box otherwise the bike will be hard to start.

When you twist the throttle you open the carb slide. This opens the carb to the open air and brings other jets into play. This isn't good because it negates the enrichment provided by the choke and screws up the air/fuel mixture that is needed to start the engine. Ed

@Tyler - any tips/tricks on checking for spark? Also, per the recommendation of the last owner, I cleaned the carb/jets out last weekend, and expect to be cleaning the tank and petcock this weekend to make sure the whole fuel system is up to snuff.

Thoughts?

@Ed - thanks for the explanation! That is the kind of explanation I really appreciate.

Checking spark is easy enough, remove the spark plug, put the plug into the boot on the wire. Hold the plug buy the boot touch it to the side of the cylinder head so the bottom of the plug is touching (it has to be grounded to the engine to work). Hit the starter button for a second and you should see a nice bright spark, if not then you need to look into the ignition system.