Idle not settling down so well '82 R65LS

[Red_Hen]

Hi Gang,

Went for @ 125 mile ride yesterday - valves just re-adjusted and heads were re-torqued because they needed to be.

When decelerating and coming to a stop, idle is high, @ 1500 or so.  Stopped the engine for gas, started her up and she idled @ 1,000 RPM's which is where I want her to be.

I re-checked carb balance last night with my Carb Mate and they were very close to being in sync - don't think that's why.

The Bing book says "idle hunting" could have to do with a leak between carb and heads, on that small hose - so I repositioned clamps & retightened.

What else could be causing the idle to not settle down when coming to a stop?

Ken
p.s.  Wow - is this bike FUN to ride!

[darrylri]

If you have an air leak, you won't be able to get a stable idle, the engine will speed up and slow down over the course of a few seconds.  

If the idle stays high after running the motor at higher rpms, or only gradually slows down while waiting at a light, it might be a sticky centrifugal advance holding the timing advanced.  You could see this with a strobe light.  A small shot of silicone spray in the little port on the "bean can" would probably lube it to work correctly.

[Red_Hen]

If you have an air leak, you won't be able to get a stable idle, the engine will speed up and slow down over the course of a few seconds.  

If the idle stays high after running the motor at higher rpms, or only gradually slows down while waiting at a light, it might be a sticky centrifugal advance holding the timing advanced.  You could see this with a strobe light.  A small shot of silicone spray in the little port on the "bean can" would probably lube it to work correctly.

Thanks, Daryl - I'll give that a try as Carb Diaphrams are new and bike otherwise accelerates & runs unbelievable!

I just bought a used Induction Timing Light -with what you described, would I point the timing light in the inspection hole?  
Will try the silicone spray - had a hunch it could be a timing issue.

[tvrla]

It's either what Darryl says or it could be the idle mixture wasn't set when the engine was really good and warm.

Another source of air leaks is compromised jet orings - especially the idle jet and air bleed adjuster screw.

Unless the intake rubber looks really bad (cracks) I haven't found them to be much of a problem. But when the intake spigot loosens, it makes a big difference. Try twisting the carburetor to loosen the spigot, and if it rotates, it needs attention.

[Barry]

2 possible causes: sticking advance mechanism or carb idle settings.

A quick spray lube of the advance mechanism will do no harm but these symptoms come up regularly on all the airhead forums and the cause is more often carbs than it is advance mechanism.

Did you recently do some work on the carbs ?

[Bob_Roller]

Classic cause is not having the engine up to operating temperature and performimg a carb synchronization .

[darrylri]

If it's the advance, you'll be able to see it quickly by pointing your timing light in the inspection hole on the left side of the bell housing, after removing the rubber plug.

If your bike is setup right, at idle you'll see an S; when you rev it up until maximum advance (probably about 4k rpm), you'll see an F.  If your bike has a sticky advance that doesn't come back to rest at idle, the S will not be centered in the window.

BTW, I agree with several of the other posters that your idle may not be set correctly at the carbs.  But this is easy to check.

If you have an air leak, you won't be able to get a stable idle, the engine will speed up and slow down over the course of a few seconds.  

If the idle stays high after running the motor at higher rpms, or only gradually slows down while waiting at a light, it might be a sticky centrifugal advance holding the timing advanced.  You could see this with a strobe light.  A small shot of silicone spray in the little port on the "bean can" would probably lube it to work correctly.

Thanks, Daryl - I'll give that a try as Carb Diaphrams are new and bike otherwise accelerates & runs unbelievable!

I just bought a used Induction Timing Light -with what you described, would I point the timing light in the inspection hole?  
Will try the silicone spray - had a hunch it could be a timing issue.

[tvrla]

I've never understood how shining a timing light will tell you if the advance is sticking?

Now if the S mark still shows when the engine is revved, I'd know for certain the advance mechanism is sticking. But... if the advance mechanism has advanced the timing, and the engine is running fast, how will you know if the timing is advanced because the engine is running fast, or if the engine is running fast because the timing is advanced???

[darrylri]

If the motorcycle idles at a normal rpm, but sometimes doesn't slow down (at, say, a traffic light) all the way, even though the throttle is closed, there can be a few different explanations.  

The advance doesn't normally operate at idle and for a little ways above idle, so if you see the timing advanced a little above idle, the conclusion is that it didn't return to base after being run up.

But if the S mark shows in the window when the engine is idling normally, but is out of the window when the bike is idling high, probably you have a sticky advance or weak return springs (or both).  

This is different than the typical air leak, because the symptom is that the bike idles ok when started and warmed but sometimes doesn't return to the low idle, or takes a while to return to the low idle, after being run up.  With an air leak, you usually get a high idle all the time or it is ragged, moving up and down frequently and irregularly.  

[Barry]

And the reason too much ignition advance at idle can cause the revs not to drop back is because the idle ignition advance setting of 6 Deg BTDC is not the most efficient setting for the engine.  It's a compromise to enable easy starting. The engine would idle faster if the ignition was given more advance.

Some electronic ignitions use this effect to achieve crude idle speed stabilisation by having a blip in the advance curve below the desired idle speed.

[Barry]

The reason improper carb settings can cause these high idle symptoms is more complicated. I think there are two possible scenarios.

If the idle speed is set too high then with a closed throttle the butterfly is a little more open than it should be which begins to bring the transition ports into effect adding more fuel to already too much air resulting in the revs hanging up as the air flow and hence vacuum over the transition ports is too high for them to drop out of circuit as they should at idle.

Another perhaps less common cause of the transition ports flowing fuel at idle when they shouldn't is still down to the butterflies being too far open but for a slightly different reason. If the idle mixture is set far too weak or far too rich and this is compensated for by the throttle stops being opened more than would otherwise be the case with the correct mixture then the same situation of the butterfly being too far open exists even though the actual idle speed may not seem that high.  The objective is always to achieve the correct idle speed with the minimum possible butterfly opening. I think the suggested base settings for the throttle stop screws of 1 full turn in from the butterfly being fully closed is too much.  1/2  to 3/4 at the most is probably a better starting point and certainly a more likely finishing point.

[Red_Hen]

Thanks much - as much as I enjoy this forum, I also feel like I'm back in school learning motorcycle mechanics!

I've learned not to take anything for granted with these machines - they are highly engineered and there's a rhyme & reason for EVERY component on these bikes.

After my long ride on Monday, I re-balanced my carbs.  Based in your advice, I checked the clamp positioning on the rubber hoses between the cylinder and carb and made some adjustments.

Went for a nice ride today and bike is idling just fine.  I plan to remove Bean Can over the winter to inspect, clean, lube and replace springs (I got a suggestion on how to do it through the inspection plate on the can - kinda like microscopic surgery only using a bent paper clip to change out the springs - Motobins sells the springs.  Bought a used induction timing light on Ebay and will use it to check timing when I reinstall Bean Can.  Right now though, I'd say timing is pretty right on.  

Learning is good - thanks for the fellowship here at R65 dot Org.

[Barry]

Glad it's fixed

Seems that may be another case that was down to the carbs rather than the advance mechanism. It nearly always is.

Most times the advance mechanism gets the blame because everyone can easily see how it might stick where as the carb related causes are more difficult to visualise.

[montmil]

Glad it's fixed...  Most times the advance mechanism gets the blame because everyone can easily see how it might stick where as the carb related causes are more difficult to visualise.

Owners that blast WD40 into the bean can -in hopes of freeing up the sticky advance weights and shaft- usually end up with stickier advance mechanisms after the kero-based solvent turns gummy. Lots of engine heat transfers to the can and speeds up the gunky mess.

If you must, flush out the can with a light solvent and drain all. A lightweight oil, applied with a thin tubing applicator, is a far better choice.

Monte