Idle problem

[JJH]

1979 R65
After the engine is warmed up (~10 miles or so), when coming to a stop the idle will be 2000 rpm.  With the brake engaged I can let out the clutch until the rpm drops to 1100 rpm.  The engine will then idle at 1100 rpm.  It will occasionally move up if I lower it to 1100 rpm at a stop, and it will occasionally drop from 2000 rpm at a stop, but this is kinda rare.  What is causing this, there are no other symptoms that I detect.  What is the cause?  What is the solution?  Is it very bad for this to happen?  Should I stop riding immediately?  Thanks for all the help!!

John in Missouri

[montmil]

Not an uncommon occurrence. No need to stop riding.

Possible advance weights sticking. Perhaps check points gap and timing.

[Barry]

Idle speed hang up can be due to sticking advance mechanism or weak advance springs or carb settings.  The advance mechanism on a 79 is not easy to access although there is a small oval inspection plate on the side of the bean can through which you can lubricate the mechanism. Dismantling the bean can to properly access the mechanism is not for the faint hearted.  

The very first thing you should try because it only take a few minutes is to lower the idle speed. A 79 has a relatively heavy flywheel and has no need to idle higher than 800-1000 RPM.  That alone may be enough to cure the problem.

[JJH]

Thanks for the hints I will try to lower the idle speed and see what effect it has.  Out of curiosity how would one go about the inspection/lubrication of the advance weights/ mechanism using the "window"

[Tony Smith]

Thanks for the hints I will try to lower the idle speed and see what effect it has.  Out of curiosity how would one go about the inspection/lubrication of the advance weights/ mechanism using the "window"
 

Remove window, fit "straw" to can of CRC lubricant (or WD-40 if you must) and let fly through the window whilst turning engine over by hand.

Please, if this cures the problem, get ready to pull the bean can apart and lubricate the advance/retard mechanism ( I recommend a good silicone grease which can be bought quite cheaply from sellers of wetsuits). While you are there I'd replace the advance retard springs on principle as they are only a couple of dollars each.


One thing you might like to look at in diagnosing your problem is the condition of the rubber tubes that connect the carbs to the cylinder heads. If they are cracked or perished (or even if the clamps are loose), extra air will get in and that may cause a high idle. Quickest way to check is to pour a jug of water over the rubber while the engine is running - if the idle changes dramatically when you do that - replace the rubbers.

[Barry]

In my experience pulling a points bean can apart is not easy. The points back plate is secured by one or two screws but is also crimped very tightly in position requiring the back plate to be turned until cut outs line up with the crimps. When I did mine it was only to find there was nothing wrong with the advance mechanism so I always advise other possibilities are investigated first.

[wilcom]

In my experience pulling a points bean can apart is not easy

My experience exactly. I said a lot of bad words in combinations never heard before,  while  putting mine back together.

[montmil]

So, John... Idle issue fixed? It's been 24 hours or so. Don't keep us in suspense.

[Tony Smith]

In my experience pulling a points bean can apart is not easy.
 

Barry, I simply can't recall any problem dealing with the "points-in-the-can" although I hasten to say I do not doubt you for a moment. I am in the happy position that the last time I was inside the points can on the wife's R65/80 was about 1991 when I removed and threw away the Pirana optical trigger system and fitted a Boyer Bransden. had no call to look inside since.

[JJH]

Monte,  I am sure I will get a complete weather report of Texas both current and historical, but it is too hot to work on the motorcycle .  After riding I remove my completely soaked jacket and gloves I just can't bring myself to stand over the cylinders.  But I will not disappoint and will work on it tonight.

[JJH]

UPDATE  Okay reset the idle to about 1000 last night.  On the way to work this morning the idle had "dropped" such that it would die at the stop light.  So in a way the issue is fixed  .  Just need to work a bit more, the bike has never liked a low idle speed.  Thanks for the help

[Barry]

Barry, I simply can't recall any problem dealing with the "points-in-the-can" although I hasten to say I do not doubt you for a moment. I am in the happy position that the last time I was inside the points can on the wife's R65/80 was about 1991 when I removed and threw away the Pirana optical trigger system and fitted a Boyer Bransden. had no call to look inside since.  

I suppose it depends on how severely the bean can has been crimped.  The body of the bean can is a substantial thickness of alloy so they must have used a huge amount of pressure to apply the crimps.  The result on mine was that the points plate wouldn't turn without  a very large torque being applied. I had to manufacture a strong pin wrench in order to shift it.  Without an appropriate tool it simply would never have come out.

When it went back I modified the plate so it was something less of an interference fit.

[Barry]

UPDATEOkay reset the idle to about 1000 last night.On the way to work this morning the idle had "dropped" such that it would die at the stop light.So in a way the issue is fixed Just need to work a bit more, the bike has never liked a low idle speed.Thanks for the help  

The down side of having the idle speed set correctly is it won't idle own for the first couple of miles.  The bit about never liking a low idle speed is odd because mine will idle reliably at 500 RPM. Not that it would be remotely sensible to aim that low but it will do it.

[JJH]

The bike still has a low idle when warmed up.  I will adjust it a bit higher when I get home.  As for the bike not liking a low idle, that should most likely be read as... "John has difficulty setting the idle low".  I occasional blame the bike to help my ego.

[Ed Miller]

Monte,  I am sure I will get a complete weather report of Texas both current and historical, but it is too hot to work on the motorcycle .  After riding I remove my completely soaked jacket and gloves I just can't bring myself to stand over the cylinders.  But I will not disappoint and will work on it tonight.

Hey, the mandatory box fans aimed at each cylinder help a lot with that.