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1981 CX500 Loses Power at higher rpms after it warms up

1K views 15 replies 5 participants last post by  Jimski 
#1 ·
I have a 1981 CX500 D with a very similar problem that other members have experienced. Bike starts, idles and revs normally until it warms up, it will still accelerate at lower speeds. Problem is when the throttle is opened all the way at higher speeds it will sputter and not accelerate. At times it will kick in if I gradually increase the throttle but it is short lived, it will continue merrily down the road once it is back below 5 - 6k. It has been getting worse over the past few years so I mainly stay on the city streets and avoid the highway. I checked the stator using the test worksheet and it checked out ok. I remembered reading a post about checking the stator when the engine is at normal operating temperature. I believe only a couple of the readings passed the rest failed, all of the ohm readings increased at operating temperature. Is that normal to have all of the ohm readings increase? I need some advice on what I should do or not do next. Thanks

cold readings warm readings
1/5 119 139
2/5 97 113
3/5 215 257
4/5 114 133
6/5 99 116
7/5 215 252
8/9 89 107
5/9 406 487
 
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#5 ·
OK... CX500D ... after # PCO1E 4001273... is in the lower range of 315 - 385 ohms. So at 406 cold and 487 hot this is likely your problem. Fubar CDI low winding.

Your advance pulsers are also out of spec, probably adding to the problem.

I do see that all readings are uniformly high. What does your meter say if you touch the probes together?
 
#12 ·
I think I would start with something a little more simple.

Have you checked the resistance of the primary and secondary side of the coils when they are warm? Chances are these could be failing at operating temperature. Easy to replace and low cost, <$50.

I had this coil issue on my '81 CXC. Then about a year later, my CDI took a dump. Replaced it with a FinnBox. Fortunately, my stator test remain in acceptable range. But I'm due for a cam chain, tensioners......etc. I'll replace the stator at that time.
 
#13 ·
Something else to try ...
Do you have a vacuum petcock? I've run into this issue recently on another bike...the petcock is not allowing enough gas to "keep up". The plunger washer inside is sticky... (In my case, I have Prime to turn the tap to full flow which fixes it, but my gl500 does not have "Prime").

The symptoms are: bike revs high when taking off but at sustained high speeds, the bike begins to falter. A bit of choke helps momentarily. It is like running dry and needing to switch to reserve. Reserve does not help in this case. A Temporary fix is to flip the fueltap diaphragm around (if possible on these honda types) or remove the vaccuum line, (plug the carb manifold vent !) and replace diaphragm with a "made" gasket.
 
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