Troubleshooting. Bike won't turn over.

[Alex Salinas]

About six months ago my dad and i finally got our '73 xs650 started after 8 years of trial and error. While it was running, the brake light burst from being overpowered and once we killed the bike, it refused to turn over again. It would start on the first kick before the light burst but has not started since. We realized that the bike was idling high, but this just seemed like a carb adjustment issue (we had just installed new ones). We have replaced the regulator rectifier, and checked all the wiring again. We have bright blue spark and all our lights come on now. We don't know what is wrong now and are all out of ideas. If anyone has seen this before any help is appreciated.

 

[Downeaster]

Basic troubleshooting:

A four stroke gasoline engine needs the following things to start and run:

1. Compression. Low compression (say, 100 PSI or below) the engine will be hard or impossible to start. Verify this buy getting a compression gauge and doing a compression check. 150 is great, 130 is doable, less indicates problems.

2. Fuel and Air in proper proportions. This is what carburetors do. Mix fuel and air and deliver it to the combustion chamber (cylinder) at the right time and in the right proportions. Too rich (too much gas, not enough air) or too lean (too much air, not enough gas) and it won't start. There are initial carburetor settings that should get you close enough. Find and read the carb guide on this site. Quick visual check: A wet spark plug probably indicates flooding or too rich a mixture. A completely dry plug indicates lack of fuel.

3. A hot spark at the right time. Spark you've got, but is it occurring at the right time? Check this by getting a timing light and seeing that the plug is firing on the timing mark.

You may also want to have a peek inside the valve covers and make sure the valves are opening and closing, both intake and exhaust.

If you've done all the above, found nothing major wrong and it still won't start, c'mon back and the folks here will be glad to help you investigate further.