Motorcycle Repair: CX 500 Custom carburator problem (looks like...), honda cx 500, valve adjustment

Question
Hello Mark,

To find this page on a search has been a great surprise! Here goes the question:

I have a 1981 Honda CX 500 Custom, with 41k miles, I got it on 1992 with 28k. It was parked for about three years and it just had a full carburator cleaning, valve adjustment, spark plug replacement, and new battery. However, itr runs very bad under 3,000 RPM. Some symptoms and other details are:
1. After being stopped for a while (i.e. night) runs great, smooth. After about 15 -20 minutes starts missing some firings in one of the cylinders.
2. At 3,000 RPM it catches up again, actually it seems that it's at about 2,800 rpms. (low jet?)
3. Misfirings include some explosions in the exhaust.
4. If ridden for 20 miles at 75 miles per hour and then going slow is the worst, it's almost impossible to ride it below 3k rpm, after which starts running better and over 4k rom is smooth again.5. when running bad it stops when in ralenti.
5. It also had this problem, or very similar, before parking it 3 years ago. However, now seems to be the other cylinder.
6. About 7 years ago I had another carb cleaning and the mechanic mentioned that these carbs were really tricky to balance. He actually used a trick: instead of gas going into the carb he used a cloth wet in gas, or something like this. He also found that one of the spark-plugs caps was bridging to the cylinder cap, which was visible, anf the cap and cable was replaced. Now it is not visible, and after being stopped for a while it starts and runs perfectly smooth for 15-30 minutes in average.

I look forward to your advice! Many thanks in advance.

Best,

Hernan
PS: Where are you located?  

Answer
Hi Herman,

I suspect more than one problem with the carburetors. A tuning issue, contamination in the fuel tank, and maybe an ignition problem.

Inspection will verify the integrity of the systems.

I return test, tune, and repair information by email. There was no email address with your question as requested.

I have some tech files for you that may help you with the problem. Reply with an email address if you want the information.

Respectfully,
Mark Shively
Dayton, Ohio USA