Honda CX 500 Forum banner
1 - 17 of 17 Posts

·
Registered
Joined
·
49 Posts
Discussion Starter · #1 ·
a little history: bike wouldn't rev past 4500rpms. i crank the throttle and it stops at 4500rpms and sputters. so i cleaned the carbs, and checked for vacuum leaks. nothing helped. i put my carbs on a friends bike, and they worked perfectly and we tried his carbs on my bike and it didn't help. after hours of checking for vacuum leaks we (my friend and i) have determined there aren't any. so we checked the coils and the stator and that all checked out.



what we do know: it runs really rich. there is gas in the intake manifolds, and on the spark plugs. but it doesn't overflow into the air intake boots/air box. and it back fires black smoke out both side when reved up to 4500rpms.



what is wrong with the bike?
 

·
Registered
Joined
·
3,516 Posts
Have you checked the intake tract and airbox mesh? You could disconnect and remove the airbox ducts and see if there's any difference.

While you're at it, swap the CDI with your friends bike and see if that makes any difference, those things seem to fail in many and mysterious ways.
 

·
Registered
Joined
·
49 Posts
Discussion Starter · #3 ·
i was think maybe a valve issue. i have yet to check the valve height. maybe the valves aren't closing all the way, or god forbid cracked. i just remembered when i got the bike i checked the timing through the left side view port with a timing light, and besides getting covered in oil i remember it checked out. i'll give both of these a look tomorrow.
 

·
Registered
Joined
·
4,104 Posts
Did you try running minus the air filter?

As you tried it with carbs that worked fine on another CX I'll accept

it probably isnt those

Valves? hmm not sure about that. I reckon it would be rough at any speed

if the valves or valve timing were suspect.

You say it cant be the stator

What do you base this assumption on?

I advise caution here

We've probably all been caught out by making assumptions at times



CDI

I had guy bring me custom that would start Ok but run rough as a bears ass

when revved

A quick test indicated a failing CDI box and substitution proved it
 

·
Registered
1978 CX500 "The Grub", 1983 GL650I "Nimbus"
Joined
·
11,433 Posts
If you know someone with an Ignitech that you could mount temporarily, you'll know if it's the stator.



Short of that, check AC output from the white and blue wires, both cold and hot. If the readings change with temp, you stator is going.



R
 

·
Registered
Joined
·
49 Posts
Discussion Starter · #6 ·
reg in bristol, what was the test you did to check the CDI?



i did these stator checks while the bike was cold:



i did both of these tests:

viewtopic.php?f=8&t=30

viewtopic.php?f=17&t=521



and all of the ohms tested within range.
 

·
Registered
Joined
·
4,104 Posts
Matt

I have a rough and ready but useful test for CDI's

Open the yellow and pink connctors from the CDI to the coils

Wiht my digital meter set read DC volts in the 250 range

I crank the motor on the starter button for a few seconds while

reading the voltage displayed on the meter

A clip to hold the black probe to battery ground is useful here

Its a pulsing voltage any meter will struggle to read so dont expect a

steady reading

but I expect to see around 150-200 Volts DC on a good CDI

(assuming a good supply from a good stator that is)



I've seen as low as 6v on failed CDI's



If you get significantly less that would be a cause for concern

Its important to remember low output from the stator will have an effect

so a substitution test can help pin down the problem
 

·
Registered
Joined
·
49 Posts
Discussion Starter · #8 ·
so i did the CDI test you posted, and i have over 400 volts coming from both the pink and yellow wires.
 

·
Registered
Joined
·
3,999 Posts
so i did the CDI test you posted, and i have over 400 volts coming from both the pink and yellow wires.


You said the bike stutters and stops at 4500rpm "when I crank the throttle",,Will the bike rev up if you open the throttle slowly?
 

·
Registered
Joined
·
49 Posts
Discussion Starter · #10 ·
it doesn't matter how i throttle up it sputters and will not rev past 4500prms.



so i'm sorry, i have been reading my multimeter wrong, its an analog that you have to recalibrate the ohms when you use it. between the white and blue wires it reads 60ohms, when they say it should be minimum 77ohms.
 

·
Registered
Joined
·
329 Posts
Matt,



I'm not sure if you saw this or not already. This is not an especially good deal, but it might get you back up and running.



CX500 motor
 

·
Registered
Joined
·
49 Posts
Discussion Starter · #12 ·
does anyone know how to, or where to find, the bypass for the blue and white wires on the stator. i forget what they are called, something like the high/low switch.
 

·
Super Moderator
Joined
·
15,413 Posts
does anyone know how to, or where to find, the bypass for the blue and white wires on the stator. i forget what they are called, something like the high/low switch.




Ok here it is.



The White Wire Fix



If the blue (high current) has failed, your bike will be very reluctant to rev much about 5,000 rpm which will restrict your speed to about 50-55 mph. Changing the stator will of course fix this, but there is a get-you-home or short-term fix for the problem, only if the blue or high circuit has failed.



Cut the blue Wire 1" back from where it arrives from the alternator to the connector box and insulate it, taping it out of the way. Patch the stub of the blue Wire from the connector box to the White wire's connection at the box. This takes the low current and sends it to both circuits. It isn't enough to give full high power to the CDI unit, but it does give much better performance than nothing at all. It is also recommended to reduce the sparking plug gap by 2 thousandths of an inch, to give the spark a shorter jump and less work to do.





I also suggest not to cut the wires back. Just use a male to female connector. I made up one of these White Wire adapters with correct colors in and out so nothing gets fried.
 

·
Registered
Joined
·
49 Posts
Discussion Starter · #15 ·
here is a new development! the left cylinder runs fine, i took the right plug cap off, and ran the bike and the left side did great, i put the right plug cap back on and it started to run poorly again. i readjusted the spark gap, and cleaned all the corrosion out of the plug caps and that has seemed to help a bit. so what ever is going wrong is in the right side.
 

·
Registered
Joined
·
8,423 Posts

·
Registered
Joined
·
1,517 Posts
Mine did exactly what you are desribing when I got it. at exactly 4500 it would load up and then started running on one cyl hitting and missing. A clogged breather tube was part of the problem... a good cleaning of the airbox/ breathers and a KN air filter made all the difference. I also had an intake tube that was crimped and leaking air at the airbox courtesy of the po. (these are a bitch to get onto/into the airbox correctly)



I don't know if it's the motor's characteristic performance, but mine still seems a little baggy in the midrange before really lighting up at around 6k.
 
1 - 17 of 17 Posts
Top