Question1982 Honda CX500 16,000 miles. Within the last month have had carbs cleaned and synched, new battery, plugs, had checked for valve clearance and cam chain tension as schedule says I should. The bike runs absolutely great until it really warms up then will sputter and cough up after you slow down or stop then take off again. Normally you can go 30 mph in 5th gear just fine and pull away fine from there but once it starts doing this you can barely go that slow in 4th. I've noticed that once you get past 2500 rpms that it smoothens right up and it perfect...it's just at the lower rpms.
I've seen your advice to others on using the choke but it doesn't help once this problem starts.
Since the carbs have been cleaned and synched it has new plugs and it only does this once it really warms up and only at lower rpms makes me think the coils under the tank ???
AnswerIf your bike is an '82, it must be a CX500C That means it has the same electronic ignition system that the GL500 and CX/GL650 models have, and they almost never cause any problems. (Earlier CX500s have a CDI ignition that is powered by special coils in the stator and are prone to failure.)
Is it possible to figure out if the problem is affecting both cylinders or just one? If it's both the problem has to be in something that is common to both sides - fuel supply (petcock problems), something electrical (a loose connection that only causes problems under those circumstances) or something like that. Or perhaps the mechanical timing advance unit is sticking - rare, but not impossible.
It is very unlikely that both coils would fail at the same time or passages in both carbs become blocked simultaneously.
If only one side is cutting out, you could switch the coils to verify if the coil is the problem: Swap the blue and yellow wires between the coils and swap the spark plug wires between the cylinders. If the problem moves you have localized it to the coil, plug wire or plug cap. If the problem stays on the same side you know that none of those parts is the problem.
Similar problems have been fixed by cleaning out the spark plug caps. They can be "unscrewed" from the ends of the wires and disassembled with a screwdriver through the end that goes onto the spark plug...
Oh heck, just have a look at this thread on the CX/GL500 forum: http://choppercharles.com/cs/forums/32059/ShowPost.aspx
If I remember correctly, your bike's coils should have removable plug wires. You can tell by the compression nuts where the wires join the coils. If they do, you should probably replace the wires some time. I don't think it is causing your present problem, but it can prevent loss of spark in wet conditions. Make sure you use new wire with a copper core, not "resistor wire" like they use on most cars these days.
It could still be a carb problem, too. You said that you "have had carbs cleaned and synched" but you didn't say by who. I have heard some horror stories about so-called pros whose definition of "cleaning" carbs leaves a lot to be desired. To properly clean carbs they must be removed from the machine, disassembled and have, at minimum, carb cleaner sprayed through every passage, followed by high pressure air (min. 60 PSI). Any signs of dirt or other deposits should be completely removed and all jets carefuly inspected and cleaned. Your carbs are 26 years old and that's a long time for rubber parts in contact with fuel. Unless it has already been done recently the rubber parts should be replaced with the best quality new parts available. I recommend a kit from www.randakks.com - Randall is one of the top GoldWing restorers and carb specialists. He couldn't get some of the parts needed in the quality he demands so he has them made for him from materials that are much better than was available when these bikes were made. I have rebuilt the carbs of both my bikes with Randak's kits. While you are at it. have a look at the information on his site about cleaning GoldWing carbs - they are a bit different from yours but the same principles apply.
I also recommend joining the CX/GL500 forum http://choppercharles.com/cs/forums
There are a lot of people there with a lot of experience who are more than willing to help. I hope I meet you there...
