Motorcycle Repair: 1973 CB450, float bowls, starter clutch

Question
Hi,

Recently I bought a 1973 CB450 with roughly 8,000 miles on it. It was in great condition for being as old as it is. The few times I started it I would start up pretty much right away.

The other day I tipped it onto its left side - it was not moving. Even since then it would not start up. We took some time today to troubleshoot. The starter works and engine turns, but it does not start. It does not have the low growl anymore. So, the carbs seem clean - we emptied the gas and put new gas in - we checked the coils and spark plugs. The only thing we noticed was that the left spark plug was not really sparking, at least not to the amount of the other side. But wouldn't the bike start with only one of the two spark plug working?

Any thoughts on how to trouble shoot to test to see what the problem is?

Answer
Danny, were the spark plug really wet with fuel when you removed them? Are they black and sooty on the tips? They may be fuel fouled and not able to spark normally.

Any number of things may have happened to the bike when it tipped over.....

Battery acid can leak out of the vent tube. Low fluid levels in the battery will weaken the output.

The starter clutch rollers may have gotten dislodged if the springs were weak, which will cause it to slip.

The coils and condenser lead connectors are all under the fuel tank and may have gotten jarred when the bike went on its side. Remove the fuel tank and check for solid connections to the coils and condensers.

The spark plug cap might have gotten damaged on that side from the fall. Check for cracks. Check the spark plug for signs of damaged insulator, as well.

Any water/debris from the float bowl may have been transferred to other parts of the carburetor, when it was on its side. Drain the float bowls and check for signs of contamination. Today's fuel is only good for a few weeks before it separates into alcohol/gasoline on two levels. The bike won't start on the alcohol portion which goes to the bottom of the mixture in the bowl.

Clean the ignition points and check the timing. In some cases the 450s have suffered from poor condenser grounds to the frame, so remove the condensers and clean the connection between the two surfaces.

Using a new/fresh spark plug, confirm that there is a steady spark to the left side. Check the coil lead into the coil for signs of damage or deterioration.

The bike may "start" on one good cylinder, but it won't be happy about it.

Bill Silver