Motorcycle Repair: 1973 Honda CB500/4 Stalling.., 1973 honda cb500, fuel starvation


Question
Hi there.  I recently broke my foot, so my old Honda sat for 2 weeks.  Started
it the other day (tough start), it idled fairly regularly for 5 min, or so, then
died..  After that it wouldn't start.  Left it for a few hours & tried again.  This
time it started fine, so I drove it around the neighborhood for a few minutes &
then it died again.. Once it started to stall, the more gas I gave, the more it
wanted to stall.  Same routine 4X now.  Bikes oil/filter & SP's were changed 3
mths ago.  Bike has been a daily rider all summer.  Rough morning starts &
runs super hot (K&N's w/ need for carb adjust), though it always ran.  Is there
a fuel/carb blockage.  Carbs were always over flowing, but never got around
to changing gaskets.   Any Ideas? Need more info?  Thanks so much!

Answer
Greg, sounds like fuel starvation. If you park the bike on the side stand, any water, gunk stuff can settle to one side of the tank. That happens to be the side where the petcock is, so you may have plugged up the petcock screen.
It is inside the fuel tank, so drain the fuel into a container where you can examine it, then remove the petcock from the tank and pry out the screen that is pushed up inside the fitting. You may destroy it in the process, as they often get stuck inside. If you have a good small flashlight you may be able to get a glimpse of the petcock screen through the gas cap opening.

Once you pass that hurdle, check the fuel tank gas cap for any blocked passages for the cap venting.
Drain the float bowls into a container so you can see what's down inside those. If they were overflowing, the needles are worn, floats out of adjustment or there is dirt, water, rust in the seat area.
If you don't pull the carbs to get them fixed properly, they will start overflowing again once you put the fuel tank back on and turn on the fuel. The floats tend to drop down and sometimes get cocked in there, so the needle won't come back up into place. If that happens, turn off the gas, tap on the carb body with a plastic screwdrive handle or similar tool to help jog the float and needle back in place.
You really need to jet up the carbs for the air filter swap. Plus, do a full tuneup so you know that the valves are adjusted, camchain adjusted, points are clean and adjusted, timing set properly, spark advancer working okay, fresh plugs and an oil change.....

Bill Silver