aclayonb
Junior Member
Had this issue on the above mentioned bike for a while. It was a cracked insulator boot. As I said, you have a lot of rubber on those old bikes. Old rubber gets hard and brittle, especially when exposed to a lot of heat - such as a carb insulator (the rubber between the carb and the engine). At idle, there was no problem. Once the engine got hot, the insulators leaked air and the idle did whatever it felt like that day, which was typically jumping to 3k-5k RPM's. It took me forver to find the issue because I would take off the carbs (assuming it was a carb issue) and then put them back on. It would seal for a bit, and then leak. If I wasn't so lazy, I would have taken off the carb insulators and carb boots first and checked them - and maybe noticed the hairline crack on the insulator between carb banks 2-3 (which is virtually impossible to see while on the bike).
The issue was espeically wonky because the crack was on the inside of the #2 insulator. The #2 on the Honda is the carb that all of the other carbs are sync'ed to. When it's not perfect - none are right.
Anyway, it seems like a pain now but start by checking anything that could be heat damaged (and take it off for full inspection). After everything not inside the carbs, between the engine and the intake hole forward of the air filter, is checked, then start on the electrical system. Verify the charge rate of the alternator at the battery. If that's good, check the spark plug wires. If they're brittle, replace them (with a used set of modern supersport coils and new wires, preferably). If the wires and plugs are fine, go to the pet**** and check the fuel line. Make sure that a new, high quality filter is installed in the fuel line to the carbs. Then drain the entire fuel line and remove the carbs. Re-clean the carbs with brake cleaner and use an appropriately sized guitar string (probably high E) to get down into all of idle passages (sometimes rust from the tank clogs these). Do not use carb cleaner - it kills your rubber seals.
While you are doing all this, check the valve lash just to be safe. If ALL of these things are good - call a priest...your probably going to have to drive out the demons the hard way.
The issue was espeically wonky because the crack was on the inside of the #2 insulator. The #2 on the Honda is the carb that all of the other carbs are sync'ed to. When it's not perfect - none are right.
Anyway, it seems like a pain now but start by checking anything that could be heat damaged (and take it off for full inspection). After everything not inside the carbs, between the engine and the intake hole forward of the air filter, is checked, then start on the electrical system. Verify the charge rate of the alternator at the battery. If that's good, check the spark plug wires. If they're brittle, replace them (with a used set of modern supersport coils and new wires, preferably). If the wires and plugs are fine, go to the pet**** and check the fuel line. Make sure that a new, high quality filter is installed in the fuel line to the carbs. Then drain the entire fuel line and remove the carbs. Re-clean the carbs with brake cleaner and use an appropriately sized guitar string (probably high E) to get down into all of idle passages (sometimes rust from the tank clogs these). Do not use carb cleaner - it kills your rubber seals.
While you are doing all this, check the valve lash just to be safe. If ALL of these things are good - call a priest...your probably going to have to drive out the demons the hard way.
