Motorcycle Repair: Bogging Down - Honda Nighthawk, intake vacuum leaks, electronic ignition system

Question
Hi,

I recently bought a 1983 Honda Nighthhawk 750.  Shortly after I purchased it i discovered that it was killing the battery.  After troubleshooting the components I found the stator and regulator dead.  I am currently sourcing these parts.

I also noticed that the bike bogged down with the choke on and when I revved the engine.  It starts well with the choke but quickly bogs down with choke on.  I have to turn off the choke rev the bike for a while for a while until it gets warm.  When warm it idles ok but bogs down when reved high.  The old plugs look black and suity.  After putting new plugs they also got dirty.

Things I have done so far:
1. Compression check - all four cylinders ~140 PSI
2. New Plugs
3. Fresh Gas
4. Cleaned the jets and float bowls (they were not that dirty).

Question:  What is likely causing the bogging? Lean? Rich? How to adjust?  Is it likely that the malfunctioning charging system is causing the poor performance?

I appreciate any help you can provide.

Thanks.

Answer
Jerry, These bikes have an electronic ignition system that requires a fully charged battery and functioning charging system in order to run properly. Fix that first, so you know that low voltage is not the main source of your problems. Note that failed rotors are very common in this type of charging system.


Other causes of bogging can be fuel caps that don't vent properly, intake vacuum leaks, blocked petcock screens (inside the fuel tank) and/or vacuum diaphragms that have failed.

Bill Silver