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1981 CX500C
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Discussion Starter · #1 ·
So my 1981 CX500C starts missing around 5000 RPM. The right cylinder seems to be running cooler, so I assume the miss is in the cylinder, but...it only happens while driving. Sitting there I can rev above 5000 RPM and it seems smooth, except for the some random backfiring. My exhaust has at least 1 leak, thats alo on the list to fix.

I plan on switching the coils to see if the miss moves to the left side, but in the meantime I checked my stator leads and got the following ohm readings

1/5 84 (should be 95-116)
2/5 97 (should be 81-99)
3/5 165 (should be 185-225)
4/5 91 (should be 95-116)
6/5 85 (should be 81-95)
7/5 166 (should be 185-225)
8/9 69 (should be 77-95)
5/9 239 (should be 384-473)

So basically slightly below to significantly below spec on everything except the 2/5 and 6/5, the left hand and right hand high speed coils. What I am not 100% clear on is, do low readings signal failure? If that's the case then shouldn't my high speed coils be the ones that are out of spec?
 

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1982 CX500EC
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So my 1981 CX500C starts missing around 5000 RPM. The right cylinder seems to be running cooler, so I assume the miss is in the cylinder, but...it only happens while driving. Sitting there I can rev above 5000 RPM and it seems smooth, except for the some random backfiring. My exhaust has at least 1 leak, thats alo on the list to fix.

I plan on switching the coils to see if the miss moves to the left side, but in the meantime I checked my stator leads and got the following ohm readings

1/5 84 (should be 95-116)
2/5 97 (should be 81-99)
3/5 165 (should be 185-225)
4/5 91 (should be 95-116)
6/5 85 (should be 81-95)
7/5 166 (should be 185-225)
8/9 69 (should be 77-95)
5/9 239 (should be 384-473)

So basically slightly below to significantly below spec on everything except the 2/5 and 6/5, the left hand and right hand high speed coils. What I am not 100% clear on is, do low readings signal failure? If that's the case then shouldn't my high speed coils be the ones that are out of spec?
Before you do anything like stator renewal, take the simple path first of overhauling your plug leads, plug caps and put in new spark plugs.
With similar symptoms on my bike, the suggested steps completely cured the symptoms, but my bike has TAI ignition not CDI.
 
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81 Gl500i 83 CX650E
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Miss above 5000 rpm can be a dirty mainjet in a carb doesn't take much gunk to make them miss, been there!
 

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2021 Benelli Leoncino Trail - 2021 CSC SG400 - 2017 SSR Buccaneer 250i - Several CX project bikes
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Do you have an original CDI spark box on that thing? If so I'm genuinely surprised. I haven't seen a good working CDI box in YEARS.

Do the stator test, do the white wire fix, but chances are pretty good that 42-year-old high-voltage capacitors are in the process of failing.

Charles.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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12,263 Posts
Do you have an original CDI spark box on that thing? If so I'm genuinely surprised. I haven't seen a good working CDI box in YEARS.
There are still still thousands out there in service. Maybe on borrowed time. Depends on a lot of unknown factors. Some will age better than others.
A stator resistance check is a good next step.
 

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A clogged air filter can cause similar symptoms. A brief run with the air filter removed can rule this out as a problem. With the air filter out examine the screen in the airbox to make sure that it is not clogged.
 
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Discussion Starter · #7 ·
Do you have an original CDI spark box on that thing? If so I'm genuinely surprised. I haven't seen a good working CDI box in YEARS.

Do the stator test, do the white wire fix, but chances are pretty good that 42-year-old high-voltage capacitors are in the process of failing.

Charles.
Yeah, it does have the original CDI alright. What is the white wire fix?
 

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1981 CX500C
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Discussion Starter · #8 ·
Yeah, it does have the original CDI alright. What is the white wire fix?
Charles, wait, belay that question, I looked up the white wire fix. I may just try that first. I actually have 2 spare engines, so I will test their stators too. I can swap on of those out if they are good.

But...I am really questioning whether instead of installing some other currently working but 42 year old bit of electrical hardware, whether I should just fork out for a Rae-san or Ignitech unit. Can anyone tell me off the top of your head what stator coil needs to still be functional to use one of those units?
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Diagnostics first. Test your stator.
 

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Can anyone tell me off the top of your head what stator coil needs to still be functional to use one of those units?
From Rae-San web page.
Colorfulness Rectangle Font Line Slope
 

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1981 CX500C
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Discussion Starter · #11 ·
Diagnostics first. Test your stator.
Yeah I tested the stator first thing...
1/5 84 (should be 95-116)
2/5 97 (should be 81-99)
3/5 165 (should be 185-225)
4/5 91 (should be 95-116)
6/5 85 (should be 81-95)
7/5 166 (should be 185-225)
8/9 69 (should be 77-95)
5/9 239 (should be 384-473)

So this tells me that everything beside my LH and RH high speed coils is questionable. I also tried the white wire fix, that didnt help, which suggests that both my low speed and high speed source coils are bad (and possibly my DCI capacitors as well). Am I correct in those assumptions?
 

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So my 1981 CX500C starts missing around 5000 RPM. The right cylinder seems to be running cooler, so I assume the miss is in the cylinder, but...it only happens while driving. Sitting there I can rev above 5000 RPM and it seems smooth, except for the some random backfiring. My exhaust has at least 1 leak, thats alo on the list to fix.

I plan on switching the coils to see if the miss moves to the left side, but in the meantime I checked my stator leads and got the following ohm readings

1/5 84 (should be 95-116)
2/5 97 (should be 81-99)
3/5 165 (should be 185-225)
4/5 91 (should be 95-116)
6/5 85 (should be 81-95)
7/5 166 (should be 185-225)
8/9 69 (should be 77-95)
5/9 239 (should be 384-473)

So basically slightly below to significantly below spec on everything except the 2/5 and 6/5, the left hand and right hand high speed coils. What I am not 100% clear on is, do low readings signal failure? If that's the case then shouldn't my high speed coils be the ones that are out of spec?
hi
I came across the same or similar problems. Forget the stator and all other coils inside the engine. You may spend a lot of time and money to identify and fix the problem. The solution is the installation of a so-called Hall-plate on the place of the advance timer (located behind the cooling water tank, only 5 bolts to remove). The new plate plus two CDI units costs around $200 and you have fantastic support as well. No need to pull the engine apart. You only keep the three yellow wires to charge the battery, the rest are redundant.You can complete the whole job is less than half an hour. Go to https://www.rae-san.com. My CX500C runs better than ever before. good luck, Joseph
 

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1981 CX500C
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Discussion Starter · #13 ·
Thanks Joseph. I actually ordered a Rae-San hall effect unit a couple of days ago. Rayman was awesome, he took a lot of time to explain things to me. This forum is great, I have learned so much!
 

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Discussion Starter · #15 ·
D, I just found his profile on this forma and direct messaged him.
Type Rayman in the site search bar, and it will show you posts by Rayman. Open a post, click on his profile icon, click on start conversation.
 

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1981 CX500C
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Discussion Starter · #17 ·
Just a follow up in this post to tell how it all got resolved. First off, MurrayF was 100% right. I pulled out two other multi-meters I had and got way different stator readings than with the first meter, but it still showed that my high speed coil was bad.

So I installed the rae-san hall affect sensor kit, put everything together and test rode the bike, and it was actually worse than ever. Now I basically could not get it to run above an idle. Up to this point I had not been into the carbs for a few reasons. Mainly because the guy I bought it from told me that he had just rebuilt the carbs, but also because I had read so many post from people who took them apart multiple times and they still didn't work right. And basically I just hate messing around with carbs.

So I bit the bullet, and pulled out the carbs. When I opened the float bowls, I found that the main jets were missing entirely, only the secondary jets were installed. And the main jet holder on the right side had come entirely unscrewed and was lying in the bottom of the bowl (looking back, I assume that when the holder fell out is when it started to not run above an idle).

I needed to re-jet anyway for pods and a 2 into 1 exhaust, so I ordered the jets (from Jets R us), slapped them in, took it for a ride, and it revved up just fine!

So the morel(s) of the story, I guess, are...don't necessarily believe that if someone says they overhauled a part on your bike, that it was done, or done right. The guy obviously did work on the carbs, but didn't understand that the jets were missing, and tighten everything down. Also, don't avoid doing something because you don't like doing it. Ironically, it only took like 15 minutes to pull the carbs and diagnose the main problem, so it was not that big a deal in the end.

I don't regret putting in the hall affect kit at all, the stator readings were not great, and I feel better not worrying about 40 year old electronics failing at inopportune moments, but I didn't necessarily need that to get the bike running. I few minutes spent on a basic visual inspection of the carbs would have been well spent early on. I could have ordered the jets and had them installed by the time I received the hall kit, and I would have been on the road months sooner.

The bike still has a slight flat spot when going between idle and high throttle (I put 90 secondary and 120 main jets in), and I am still getting the occasional backfiring, but so I still need to do some fine tuning. I can at least get out and do some riding.

Thanks to Murray and Ray for all the good advise along the way....
 
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