Post by bjg on Jul 5, 2013 7:30:43 GMT -5
I had a really difficult starting problem but I’m happy to say my scooter is up and running again (It was a CDI problem). While the road has been quite painful, I did learn a few things so I thought I’d share. Who knows, maybe it will help someone. To do a quick recap, my starter was cranking but the engine would not run. I knew I needed a good air/fuel mix, compression, and a spark to get the engine running but I wasn’t clear on how to check those things. Here are some of the tests I found along the way that were helpful.
Testing for good Spark. Pull the spark plug, put it back in the boot, hold it by the boot with the metal of the plug against the side of the engine and crank. You should have a nice strong pulsing blue spark. The pulse should be rapid and almost continuous (thanks alleyoop)
Check Compression. Pick up a compression tester (harbor freight has them pretty cheap), remove the spark plug and install the tester, and crank (with the throttle wide open for max air). Compression should be more than 100psi.
Testing the Pickup Coil. Follow the wire that runs from the Pickup coil on the engine to the CDI module (usually Blue/Yellow) and measure on AC volts at the back of the pin as it enters the connector for the CDI. You should see zero volts when you are not cranking and about 0.5vac when you are cranking. (This is the trigger to tell the CDI to fire the ignition coil).
Testing the Ignition Coil The coil itself should measure about 14-16 ohms. One side connects to ground and the other to the CDI. Measure the connection to the ignition coil (usually Black/Yellow) at the ignition coil on AC volts. This should be zero when the engine isn’t turning and about 15-30vac when you are cranking.
Rule the Carb in/out. Remove the spark plug and put about a tablespoon worth of gas in the spark plug hole then reinstall the plug and start the motor. With this amount of gas in the cylinder the engine should run for 10-20 seconds or so (even if the carb isn’t supplying air/fuel at all). To add the gas safely, dip a piece of clean fuel line into the gas tank and then hold your thumb over the end of the tube to trap the gas in the tube. Next put the tube into the spark plug hole and let your thumb off the end to release the gas. (Don't do this on a hot engine...it is flamable after all)
Check the Sparkplug after trying to start. Try and start the motor for several attempts (~10 seconds of cranking each time) then pull the spark plug. If the plug is wet you have too much gas going into the cylinder and not enough air (flooding the engine).
Is the CDI Enabled? If you have a DC CDI, you should have battery voltage on one of the pins going into the CDI when both the kill switch and the key are in the on position. If you have an AC CDI, the voltage to power the CDI comes from the stator itself (usually a Black/Red wire) and the kill switch and ignition switch make a ground connection that can kill the engine when turned off.
I don't claim to be an expert so any of you experts out there feel free to chime in and adjust any of these (or add to it). I can tell you though that these tests helped me a lot. Cheers.
Testing for good Spark. Pull the spark plug, put it back in the boot, hold it by the boot with the metal of the plug against the side of the engine and crank. You should have a nice strong pulsing blue spark. The pulse should be rapid and almost continuous (thanks alleyoop)
Check Compression. Pick up a compression tester (harbor freight has them pretty cheap), remove the spark plug and install the tester, and crank (with the throttle wide open for max air). Compression should be more than 100psi.
Testing the Pickup Coil. Follow the wire that runs from the Pickup coil on the engine to the CDI module (usually Blue/Yellow) and measure on AC volts at the back of the pin as it enters the connector for the CDI. You should see zero volts when you are not cranking and about 0.5vac when you are cranking. (This is the trigger to tell the CDI to fire the ignition coil).
Testing the Ignition Coil The coil itself should measure about 14-16 ohms. One side connects to ground and the other to the CDI. Measure the connection to the ignition coil (usually Black/Yellow) at the ignition coil on AC volts. This should be zero when the engine isn’t turning and about 15-30vac when you are cranking.
Rule the Carb in/out. Remove the spark plug and put about a tablespoon worth of gas in the spark plug hole then reinstall the plug and start the motor. With this amount of gas in the cylinder the engine should run for 10-20 seconds or so (even if the carb isn’t supplying air/fuel at all). To add the gas safely, dip a piece of clean fuel line into the gas tank and then hold your thumb over the end of the tube to trap the gas in the tube. Next put the tube into the spark plug hole and let your thumb off the end to release the gas. (Don't do this on a hot engine...it is flamable after all)
Check the Sparkplug after trying to start. Try and start the motor for several attempts (~10 seconds of cranking each time) then pull the spark plug. If the plug is wet you have too much gas going into the cylinder and not enough air (flooding the engine).
Is the CDI Enabled? If you have a DC CDI, you should have battery voltage on one of the pins going into the CDI when both the kill switch and the key are in the on position. If you have an AC CDI, the voltage to power the CDI comes from the stator itself (usually a Black/Red wire) and the kill switch and ignition switch make a ground connection that can kill the engine when turned off.
I don't claim to be an expert so any of you experts out there feel free to chime in and adjust any of these (or add to it). I can tell you though that these tests helped me a lot. Cheers.
