Is the idle supposed to hang after a highway run ?

[Johnster]

Hey guys,
  '79 R65, showing 30k on the odo - been in storage for the last 6 years and I got it running earlier this year.
  Starts very easily - but once its warmed up fully (that 15 minute highway run they all talk about) the idle 'hangs' up at 1500rpm or above.

Checked valve clearances last night - they were tight, but I opened them to .006 and .008 so I think that they are better.  hanging idle did not change

  Throttle cable has plenty of slack at all steering angles.  Choke cable does not - nothing left on the screw adjuster I might need to pull the carb and loosen the attachment point for that.

Power feels good at all times (my last bike was a 750 4cyl, so my feeling might be off...)  I can do 80mph if I ask it to.

  What next ?  ignition timing ?  then carb sync (I have Hg sticks...) ?  Spray WD-40 on carb boots to check for leaks ?

(oh, and if you want pictures....)

-John

[nhmaf]

Well, given the age, it could be that the advance mechanism is sticking in the points beancan, but you are doing the proper thing to first eliminate the simpler things, including valve lash, carb adjustment/cables/synch, and checking for air leaks particularly between the carb and the head.   It is more likely at this point that the carbs do need adjusting (possibly cleaning or at least checking too).   1500 rpm isn't far above where it should be, so it could be simple cable and carb adjusting is needed, or it wasn't done before with the engine thoroughly warmed up first, which can cause the same thing.

[steve hawkins]

I would go with the thoroughly warmed up scenario.  Do your idle and carb sync at the end of a ride.  The engine has to be properly warmed up.

Having said that, at 1500 rpm you should be keeping your battery charged.  I.e. keeping the charge light out.

I personally do not adhere to the 'lets get it idling as slow as possible brigade' mentality.  I don't want it stalling at junctions and in the winter traffic I want to keep my battery charged.

But then I do not have a rev counter, so I do not really know what I am idling at.

Toodles

Rev. light

[Barry]

Before you go for the next ride I would just turn out the throttle stop screws by very small equal increments no more than the width of the screw driver slots to lower the idle speed. It'll take 20 sec max to try. If it works you can carry out a proper carb sync in your own good time.

It could be the advance mechanism but most times it's just been tuned before it was properly warmed up.

If everything is good with the battery/charging system a 79 should idle at 1000 - 1050rpm with the gen light out. The factory spec for idle speed was 800 - 1100 RPM but if you were to set it at 800 fully warmed up then from cold you would have to ride several miles before it would idle at all. I've used 1000 - 1050 for the last 7 years and it will idle reliably at 800+ rpm after a mile or two.

[Luca]

I'm with the others on improper idle adjustment.  Probably both the mixture and idle stop screws will need adjustment.

A sort of way to test a sticky advance unit:
-While exhibiting the high idle, put the bike in gear at a stop.
-Hold the front brake and start to slip the clutch until the engine bogs down.
-Pull the clutch again.

If the idle now stays down, it's an indication of a sticky advance.  If it goes back up it's an indication of prematurely tuned carbs.

[montmil]

The "dragging the clutch" is a good technique to begin isolating a high idle problem. Should the high idle revs return,

Check the throttle stop screws first.

No joy on the top screws, then try very small tweaks of the idle air screws on the bottom of the carb body. Perhaps first mark the screw slot location with a pencil. SMALL adjustments and blip the throttle and allow the revs to 'settle'.
   Good results could come from just one screw or both. It'll take your manometer to determine the exact sweet spot/s.

All carb tuning must be done on a fully warmed up engine. Depending on your ambient air temps, that could mean a ride from 10 (warm air) to 20 miles (cooler air). Don't cheat yourself -otherwise you'll just be wasting your time.

And keep a big fan blowing over the engine while you work your magic.

[Johnster]

Excellent ideas guys - thank you.
  I did try the 'idle drag' test - and it wandered back up to 1500 or so...at two different times during the ride (after fully warmed) so that does remove the ignition advancer - I was hoping to avoid entering the front of the engine.

My last bike ('97 Suzuki Katana) ended up with the same problem - I went through the carbs (4 of them) 3 times and never made it run better...one of the few times I took something apart (3 times) and it ran worse than when I started...makes me scared of carbs now.  Perhaps reading some more snobum is in order.

What kills me is that it runs so well when cold- and starts so easily (when cold or hot)

-John.

[montmil]

It'll be a simple thing, John. Usually is. It's an Airhead.

[Barry]

John

Just turn out (anticlockwise) each throttle stop screw by the width of the screw driver slot. I'l take you 20 seconds and it's reversable. You can't do any harm.

[Luca]

As the others have said, just back out the idle screws a bit.

As long as the throttle cables maintain slack and you dont touch them you will not affect anything but idle.  Even messing with the mixture on a fully warmed engine (which most do by ear) will not have much effect at mid range rpm's and up, where the bike should be ridden.

You can make a very accurate differential manometer for very little money to sync the carbs at some point in the near future.

Now about that choke cable... the fittings are adjusted out to tighten slack.  Are you sure all the choke cable fittings are screwed in all the way?  Can't recall if the 79/80 had two cables at the lever or a barrel splitter.  If there is only one cable at the lever, make sure the adjuster at the barrel splitter under the tank has not been backed out too much.

[Johnster]

Choke - My '79 has a single lever- mounted to the airbox, with 2 cables coming out of it (one to each carb).
  Funny thing - the choke cable looks like a solid wire (think old lawnmower throttle) - not a stranded/twisted cable like *every other motorcycle cable I've ever seen* I need to lube it with something anyway.

I'll get to the carbs soon - thank you all, again.

-John

[Barry]

Yes like mine the choke cables on the early models are stiff solid wire so that they can push as well as pull which is needed because there are no return springs. All you need to do is ensure that with the choke lever off the operating arms actually hit the stops on the carb and with the lever full on they hit the other stops. Easily done by a look see as you operate the lever.