1986 R65 Misfiring

[R80rider]

Several months ago, my 1986 R65 developed an intermittent but predictably repeatable misfire.  It is repeatable in the sense that starting normally and riding 35-40 miles at highway speed seems to bring it about every time. When the problem manifests, I notice a little extra vibration in the handlebar and the foot pegs.  There is no audible backfire, nor is there much loss of power. Also when it occurs, I can shut the cycle off and wait a few minutes and when I restart, the misfire is gone.  Both my brother and I who own a few of these older airheads have looked into this matter along with a very experienced airhead mechanic.

I am in the fortunate position of having a 1987 R65 that I can use to swap known good parts from and have done this in a fairly methodical effort to isolate and isolate this issue.  To date, the following parts have been moved over one-by-one from the donor R65:


1. Spark plugs and spark plug wires
2. Coils
3. Ignition controller (under the tank) unit
4. Ignition trigger (bean can)
5. Headlight relay (under the tank)
6. Voltage regulator

    

Additionally, we have checked the ground wire on the dual coil, checked the valve clearances, and set the timing. The problem has persisted through several tanks of fuel, and none of the steps listed have changed the symptom as described above in any way.  It should also be noted that the cycle ran fine for several thousand miles before this problem occurred.  The first time it was noted was on a trip from Chicago to Phoenix while riding through Texas.

When it occurs, vibration can be felt while riding.  It was suggested that an inductive timing light be carried with me while test riding to allow both sides checked when the misfire starts occurring.  I have done this and can verify that the light strobes confirm a misfire on the right side of the cycle.  I cannot completely rule out that it might be occurring on the left as well but that has not been empirically observed.

With regard to the instruments and warning lights on the cycle, the tachometer does not appear to bounce and I have not noticed any flickering or other unusual behavior from the warning lights or any other electrical instruments on the cycle.

The cycle is stock with no third party ignition or carburetor modifications.  Both these systems are set to factory specifications.

With regard to the donor 1987 R65, it is running without issue using the components swapped out of the problematic 1986 R65.

At this point, I am looking to this forum for help in resolving this issue.

Please feel free to ask questions and I will make every effort to answer them as quickly as possible.  I am open to suggestions no matter how obscure they might seem.  My hopes are that someone has experienced this or a similar issue and might have the solution or possible solution in hand.

Thanks in advance and I look forward to hearing back from you.

[SoloLobo]

My R65LS has very noticeable vibrations at the footpegs and handle bars.

I've had success "tuning" the RPM's they occur at by adjusting (fine tuning) the carb sync

As you have tested all the ignition system parts with no effect on the behavior, it would seem to point to this being a carb tuning issue.

The R65 vibes (behavior) nothing like the R100GS, R100RS's, R80G/S and R60/5 that I have owned in the past... completely different animal in terms of vibrations

Also, drop the float bowls and look for a lens of water in the bottom of the bowl.

[Barry]

Sounds like you have approached the problem in a thorough and logical manner with the parts substitutions. Ignition would therefore seem to be ruled out as the cause of the misfire. Short of something very strange that would cause a loss of compression that really only leaves carbs. Are the carbs the same on the donnor bike which would allow a swap ?

[R80rider]

Thanks for both of the replies!  Yes, the carbs are the same.  I suppose if I am going to swap them, I should do one at a time to isolate the problematic carb.  

Any ideas what would change in the workings of a carb at 40+ miles that would cause this issue?

[Bob_Roller]

I had a somewhat  similar issue with my '81 R65 about 22 years ago, but I had a complete loss of the electrical system when this happened .

At that time I was told to go through the electrical system and pull apart the electrical connectors and check the ' pins ' for security and corrosion .

Found a few that were not locked into the plastic connector body .

Never found the ' smoking gun ' that was causing the issue, but it hasn't returned .

I also had a failing ignition switch give me almost the same conditions a few years later, finally one of the contacts broke off and you could hear it rattle around inside the switch after I removed it and shook it around a bit .

I don't know if the mono shock bikes are the same as the twin shock bikes in this matter, but most of the grounds for the bikes electrical system are ganged together at connect to the frame at the voltage regulator attach bolt .

May want to check that connection for security, corrosion, broken wires, etc .

I ran an extra 10 gauge wire from this point back to the battery negative terminal, just so grounds are not an issue in the future

[R80rider]

Thanks Bob!  I will definitely try adding the ground wire.  

Something that I want to ensure does not go unnoticed is this:

If I take the cycle on the same route, the "misfire event" occurs at a predictable location at around the 40 mile mark.  I have come to recognize the landmarks in that area and know the misfire is about to occur.  

So something seems to happen every time when the cycle hits a certain temperature or some other variable I have not considered.  

[Bob_Roller]

Only thing that comes to mind, is heat sink paste between the ignition control module and it's heat sink .

But the later bikes had the control module riveted, or bonded to the heat sink, so you may have one of those types .

[Barry]

It's bizarre that the symptoms occur with such predictability at the 40 mile mark.  You would think any temperature related cause would make itself know sooner.

To re-cap you a have a misfire which seems not to be ignition related as substitution of the ignition components makes no difference. In truth all of the ignition system has not been substituted because the ignition system is dependant on the ignition switch, kill switch and wiring harness. But I think they can still be ruled out on the grounds that any fault with the ignition system wiring would have an affect on both cylinders and as far as you know only the right cylinder is affected.

So back to carbs. What would change in the workings of a carb at 40+ miles that would cause this issue?    Logically it would have to be a significant change in mixture strength but as to the cause, I honestly can't think of a mechanism that would occur with such predictability.

I guess you have to defeat this problem with logic and start by showing if it is carb related or not by a simple substitution.   If the carb is shown to be the cause only then delve deeper to determine the exact cause.

[R80rider]

We have one that is riveted and one that the heat sink comes off so you can apply the paste.  Like you, we thought that could be the answer, but it did not change the symptoms.  We also swapped the one from the '87 and it also resulted in no change.  

Really appreciate the input!!  I'll let you know the results of the ground wire addition.  

[Bob_Roller]

In the first post, the comment is made that the misfire can be confirmed with using a timing light on the right cylinder .

Carb issue will not give an ignition system misfire indication .

[R80rider]

"In the first post, the comment is made that the misfire can be confirmed with using a timing light on the right cylinder .

Carb issue will not give an ignition system misfire indication."

That is what we concluded also which is why I asked if there is a logical reason to visit the carbs?  

[Bob_Roller]

I questioned going to the carbs myself as well .

There is no easy way to troubleshoot this problem .

The only two things left in the electrical system that are swappable between bikes, is the kill switch and ignition switch .

After that, it's a wiring harness .

Have you checked the fuses for condition and security, the OEM fuses are the cause of some electrical issues, the spring tabs that hold the fuse sometimes don't do a great job .

I've replaced mine with a blade fuse holder .

Just adding possibilities to an ignition system issue that I've seen or been told about over the last 4 decades, a tachometer is connected to the primary circuit of the ignition system, an issue with the tachometer or the wiring to it can cause ignition issues .

I know you've already stated that you see no tachometer indication issues .

[R80rider]

Definitely going to run the ground wire and check the fuses and fuse holders as these are things we have not tried before and are great suggestions.

We really think this is occurring on just one side of the cycle.  If you have any other ideas of what electrically would only affect the firing on a single side, that input would be very helpful.  

I will update you once we have tested with the ground wire and inspected the fuses and fuse holders.  

Any other suggestions are always welcome.  We would really like to get this resolved.

Thanks!!

[mrclubike]

To rule out the ignition system cant you simply  swap the plug wires at the coil without swapping the wires at the plugs. (or swap at the plugs  and leave the wires alone at the coil )
If the miss  does not swap then you know you have a problem at the head.
compression or fuel
Sounds to me like you have a carb issue.
Have you put  manometers on it and tried to see if the carbs  will balance at the higher RPMS's    

[R80rider]

Sorry for the long delay in posts.  

Following the suggestion that the plug wires be swapped, this was done last night.  The problem took a some extra miles to recur but when it did the symptoms were the same and only on the right side (same as always).  

Unless someone has a further suggestion, it seems that the ignition system is not the problem.  

A few of you suggested that it might be carburetion on the affected side.  If anyone can explain what might change in the mixture or engaged jets during a ride of this duration, it would be greatly appreciated.  

I am now more inclined to think it might be mechanical with something sticking or some other dynamic changing when it hits a certain temperature.  

Looking for continued help and thanks in advance!