Motorcycle Repair: 1981 Honda CX500 Timing?, 1981 honda cx500, plug caps

Question
I bought a CX500 for cheap, nice bike. I noticed that it was having trouble with it's pick-up on the highway especially. Seemed as if the left cyl. wasnt firing correctly. I assume it is timing. It is pooling a bit of fuel in the airbox (definitely from the left cylinder), intermittently seems to fire both cylinders correctly and there is a good spark coming from the left plug. I guess I have ruled out carb problem, spark problem, I have changed oil/oil filter, air filter, and shaft oil. Everything else on the bike works fabulously. Does this seem like a timing issue? Thats what I have bets on (stretched chain, out of adjustment). Do you know a ballpark as to repair cost? I know my way around a bike and am not the least bit afraid to fix it myself, but I saw somewhere that this might not be possible. What do you think?, and thank you for your time (hehe).

Answer
Josef...  Now you know why it was "cheap"! Probably the previous owner couldn't sort it out either.

First of all "timing" issues on CX500 can refer to valve timing or ignition timing. Valve timing, if it changes, affects both cylinders. There were issues with camchain tensioners in early models, but the later ones should be okay. There is an adjustment for it, however, so check to see that it is okay. You can check it by removing the crankshaft plug on the front of the motor so you can turn it over. Pull a valve cover and then watch the valves as you rock the crankshaft back and forth. If the valves and crankshaft are turning together then the camchain is okay and valve timing is fine.

Check the valve clearances and then do a compression check to see if there are issues there. Both sides should be close to the same reading.

Check the spark plug caps to see if the resistors inside are okay. Readings should be around 5k ohms. Have the coils checked to see if both are okay.

Checking the illustrations on the website below:
http://www.powersportspro.com/partsfish/login.asp

I see that they changed the CDI components from the $500 unit to a pair of $175 spark modules in 1981. Try swapping out the spark modules from left to right sides and see if the misfiring changes cylinders. If so, then you need to replace a spark unit. Honda used fairly universal spark units back then, so you may be able to find one at a salvage yard from another model machine that will work.
If not, the CDI Pulser assembly could have a bad segment. Spark and charging issues on CXs are well known and often expensive to repair, especially when the alternator stator dies. The whole motor comes out as a unit and they aren't that hard to service on the backside, but you have to be careful of the waterpump seal and the copper washer on the pump shaft end. Replace both when you get in there, if you get in there.

Checking ignition timing with a timing light is a good way to watch for problems, but the timing marks on the flywheel are running in oil, so a small special timing tool was made to watch the marks and not get wet. You can still just hook up the light on each side and run the motor watching for irregular firing on the light.

Check the web for some CX500-650 websites that can help and get a GOOD shop manual. www.helminc.com has factory info available or check Ebay for possibilities.

Bill Silver