QuestionHi Bill, I have a 75 Honda CB360T that was given to me by my uncle after sitting in a barn for over 20 years. When we first brought it back, we cleaned it up, rebuilt the carbs, replaced the battery, and did some other small repairs. It now starts right up and runs really well at first, but once it warms up, it begins to run erratically, then stops running all together.
There are quite a few small symptoms that occur, which makes me believe there may be multiple problems at hand. As I mentioned before, when starting from cold, the engine runs strong, has plenty of power and acceleration, and seems to run flawlessly for about 5 minutes or so.
The first thing that starts to happen after that, is a lack of acceleration and power. It continues to run, but if you try to give it gas, it just doesn't respond and starts to cut out as you open the throttle. At that point, sometimes I need to down-shift to keep the revs up and keep the engine running. It will continue to run like this for a couple more minutes or so, but soon after, the second you pull in the clutch or come to a stop it dies. Sometimes it will start back up, but more recently, I haven't been able to start it back up until it cools down for quite a while. I have also noticed that it will backfire quite a bit when you pull in the clutch or let off the throttle.
Since I rebuilt the carburetors, and it runs so well when first started, I don't think this is a fuel issue. I feel like it has to be some sort of ignition / electrical problem. Another thing I have noticed is that the spark plug on the left side cylinder has much more carbon build up than the right side. The right side plug looks exactly like it should, with the insulator still white and no excessive carbon build up, but the left plug looks borderline fouled, and I replaced both plugs at the same time.
I've checked the breaker points, and they are in really good condition. The gap was right around .35mm. Everything internally actually looks really good. On the outside though, is a slightly different story. There is a lot of dry cracking of rubber parts. A lot of the electrical wires are beginning to become hard and possibly brittle.
Anyways, I'm not really sure where to go from here. What would make it only run poorly after it has been running for a while? Any help would greatly be appreciated!
AnswerBrandon, bringing these bikes back to life is an exercise in patience and careful observance of all systems and components.
Step 1: Adjust valves and check compression. Should be about 170 PSI.
Step 2. Always have the battery fully charged
Step 3. Remove the points plate and check the function of the mechanical spark advancer. It must move easily against spring pressure and return to retarded position quickly.
Step 4. Re-installing the points plate, ensure that the gap is at least 3.5mm (.014-016") AND that the points open at the F and LF marks respectively. Just setting the gap does not guarantee the timing is correct.
Step 5. Check ignition coil primary windings for resistance values around 4.5 to 5 ohms. Both coils should read out about the same. Check spark plug caps for 5k ohm resistance values and be sure they are screwed tightly onto the ends of the plug wires.
Step 6. Check secondary coil wires for breaks/cracking or loose connection at the coil tower end.
Watch the ignition points for excessive arcing, which is a sign of a disconnected/loose or failing condenser.
Step 7. "Rebuilt" carbs can mean a number of things... Completely disassembling them, cleaning every part and installing OEM gaskets/o-rings/seals... OR cleaning out the bowls, sticking a KEYSTER kit in place of OEM parts or something in between. CV carbs on this model MUST have a good diaphragm (no pin holes, etc). Float level needs to be adjusted to: 18.5mm with clean float valve.
Step 8. Remove the petcock and clean out all the passages and filter screen (up inside the fuel tank).
Step 9. Check the gas cap for plugged vent hole, just outside the edge of the gas cap gasket.
Step 10. Be sure carburetors are properly synchronized.
Do the check list and see what you find.
Bill Silver
