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Discussion Starter · #1 ·
I am working on a 79 CX500. I have completely restored one of these in the past and still own it. This one is for a customer. Low miles, 12k. Great compression. Previous owner had the stator fail, he replaced it and could not get it running. That's how I got it. I found he had the Green wire on the CDI connector in the wrong spot, fixed that and have great spark. As it sat a while, I went through the carbs and cleaned extremely well, all jets and passages etc, as I usually do.
Go to fire it up and It starts quickly, idles both cylinders, but will not rev above 1500.
Choke does not seem to flood it out or have much effect, this is odd so I go through carb again. No help. I can spray gas into the intakes of carbs and this has no effect, or increase in revs. I do this with the throttle open running and it just sits there stumbling at 1500 rpm.
I can see and feel the slides moving as I open the throttle, they move freely but with throttle at half, they open more but the engine just sort of stumbles at 1500 to 2 k rpm.
I figure clogged exhaust, and no its wide open, I removed the H pipe/collector so running straight collectors only.
I can remove one plug wire and install a plug, and while running on the other cyl, this plug is nice blue spark, as is the other when I try that side.
I have swapped with a known good CDI box and get the exact same results.
All resistance checks on stator is good as it the blue and white wires. If I crank it and measure AC I get 75 volts ac on blue and 90 volts on white.
I have never had this much problem. I even put a strobe light on each cyl and while running at idle it is very steady and right on the marks.
I have changed plugs, and swapped out a coil and get same results.
Float levels are at 15.5 mm and bowls each have the same amount in them when I drain them.
Cleaned carbs multiple times now and am ready to install my set off the other running bike.

Question, Is there any way it could have jumped timing or maybe the PO somehow installed the stator in wrong? The valves open properly and the flywheel marks match TDC for each cyl.
Its almost like as it revs the timing goes backwards and wont allow it to rev up? Is that even possible.
Any help will be much appreciated. I will also post the final fix as this is great to know and I hate when guys will not follow up.
 

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do a cdi test and lets check for output voltage of the cdi

Get a meter, lift the seat, open the 2 way connector
and read the resistance between the blue and white wires
and white wire and ground
From the stator, not the CDI
blue-white 77-95
white-ground 387-487
If that looks ok
reconnect the plug
open the black/white kill switch connector from CDI to bars
and both yellow and pink coil LT ones too

Set the digital meter to read DC VOLTS on in the 250V range
clamp black probe to ground then test the yellow and pink in turn by
sticking the red prove ion each as you crank the motor on the button for
a few seconds
I'd expect to see >150 VDC flicker on the display with a good CDI box
I've seen as low as 6VDC on a failed unit

If it looks ok test again with the kill switch wire connected up
and the switch in the Run position
If you dont get the same results the kill switch is probably shorting to ground
 

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Discussion Starter · #3 ·
I forgot to mention I tried disconnecting the blk/wht and got the same results.
I have 10 ohms between blue and white. White to ground is 300 ohms and blue to ground is 310 ohms.
Pink to ground or yellow results in 85 or so vdc but drops to 20 or so after cranking a couple seconds.
I read 95 ohms on my other bikes blue/white so something is up?
This is suppose to be a new stator but you know how that goes?
 

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Describe the color of the spark plugs after trying to get it above 1500 RPM. Are they white, black, brown?
 

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Discussion Starter · #7 ·
I have the bike on a stand in my garage and can't run it that long. Plugs are new since the problem and black. Wet with fuel. Intakes tubes are wet too when removing carbs.
My first thought was crazy rich, jets in wrong or needles stuck high but carbs are in perfect shape. I even swapped with a set from my personal bike, which runs perfectly just to rule them out.
it starts great, idles fine, open the throttle and it just slowly climbs, stutters if held at wide open. Just cracking throttle gets it to just get past 1500 or so but that's it.
This is driving me nuts. I re-checked all coils readings on stator connector and they are all in spec, except for the blue to white, which is 10 ohms.
I remember having something like this before but can't recall what it was.
 

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Excuse an illiterate (don´t know much / enough about electrics / electronics), but 10 Ohms between blue and white seems odd enough to me.

One of the old gurus here (Don in Oz) once tried to make me understand how this ignition system workds and as far as I remember the "blue" (high speed) and "white" (low speed) ignition source coils are wound in series with eachother but "phase-wound" - whatever that means. Could it be that those low 10 Ohms reading is the problem?

Have you tried the "White Wire Fix"? With that one you omit the blue cable to the CDI unit and let the white coil do the whole job. Often works on CX-es with those dreaded / usual 5000 rpm stumbles that many of us have experienced.

Or can it be that the timing advance stator isn´t correctly connected?

Either way it seems like a timing advance problem to me.

But what do I know??

/Sture
 

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Discussion Starter · #10 ·
1-5 105
2-5 91
3-5 198
4-5 106
6-5 82
7-5 201
8-9 9
5-9 290
Sture, If i hook up both white and blue to the white wire on the CDI it will not fire. With only the blue hooked up it runs the same, idle and will not rev . With only white hooked up, it will not start.
I agree, its like it is retarding as it revs. I plan on putting the Ignitech on with the G8 stator eventually but I hate just throwing parts at it. I am waiting on a response from the group purchase, maybe you guys know if he has anymore?
Otherwise I found an ignitech on ebay, used but looks to be a good one. My quick reading on that upgrade makes me think it still uses the pulser coils so this may not alone make mine run.
In the next 20 minutes or so i am going to put my timing light on again and see if i can see it change time while reving the little it does from idle. I do know the spark is solid as is the timing light, no dropped pulses or anything.
Thanks guys for the quick responses.
 

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Sounds to me like a generally weak spark. It won't ignite more often than a few thousand times a minute and above that the spark falls flat. This causes sooty plugs.

It is a common source to both sides. Most likely the stators power supply to the CDI.
 

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Does the petcock flow freely? Though it shouldn't do it right away...

Fresh fuel?

Stock carbs or is there a vacuum line on there?

Tank's not pressurized?
 

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Discussion Starter · #15 ·
Spark is hot, I will try and see how far it jumps but in my experience i have seen a lot weaker run fine. Great thought though and because I can't see inside it may just be doing that. With a strobe light though, if the spark gets week it will not flash anymore and that would coincide with the stumble or lack of reving. Carbs are stock and gone through well. I even installed the set from my daily ride with exact same results. I have tank off and using a temp tank with valve so fuel flow is good.
Keep them coming.
Question, does anyone know if there is an ignitech for sale here? if not i am going to get the one I found on ebay. As I mentioned it will eventually get installed as part of the restoration so not a waste of money and may be a good troubleshooting step too.
 

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Silly question probably but air filter is fine?

I suck at electrics, but what would be the symptoms if the stator pickups were reversed?Sure the guys would have noticed in your testing, but you got me stumped too!
 

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Discussion Starter · #18 ·
CDI from my running bike has no change in all. I pulled the little rubber tubes from the airfilter so I could watch the slides and block air/choke carbs. So it is runnning on table w/o filters.
I just bypassed the spark plug boots to rule them out and no change.
The thing to remember here is that somebody else installed this stator. I don't know what comes with the RMStator kit but it looks like the original wires coming from the engine except for the green wire to cdi box, and the three yellow are now black. So it looks like the only thing new is the main stator?
 

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the rm cdi replacement stator ahs a whole bunch of fitment issues

can you find out if they used the proper shorter bolts or do you hear any weird rattling as you try to rev it up?

can you unplug the 3 yellow charging wires and try reving it up pls?
 

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Discussion Starter · #20 ·
FR timing mark is dead on the index mark for right side. What little reving there is causes no movement at all on the timing. Kind of strange how steady it is, maybe I'm used to points bikes as thats usually when I use this. On those it sort of "floats" around you know.
This is begining to be one of those where when I do find it, I'm going to feel really dumb. lol.
I will not do the left as my eyes can't take any more oil. it was dead on last I checked.
 
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