Trying to diagnose why your Honda CX500, GL500, CX650 or GL650 won’t fire on both sides when it’s running? Wondering whether it’s a carburetor/air/fuel issue, electrical/ignition issue or mechanical issue? Here’s a test to help you figure out where to begin troubleshooting.
Put on some safety glasses, start the bike, and on the side that isn’t firing remove the balance screw that sits between the carburetors and the head, circled here on the right hand side:
Squirt a little starting fluid (you can find it on Amazon, eBay US, eBay UK or eBay AU) into the hole – emphasis on little, you don’t want to cause damage – and if the cylinder fires, you have a fuel delivery problem. If the addition of starting fluid does not help then you most likely have a mechanical or ignition issue to troubleshoot.
Keep in mind that using highly flammable substances (i.e. starting fluid) near ignition sources (i.e. your motorcycle) is dangerous – please take appropriate precautions (e.g. the safety glasses mentioned above).