Idle speed varies

[Trickydisco]

Hi,

If you have seen my other post you are aware that I have just got my 79 R65, Im waiting for the workshop manual to arrive, but I have noticed something which doesn't seem right.

When I start it from cold it starts ok and idles just below 1000rpm, but when it gets hot either after a bit of aggressive riding or because of slow riding in traffic the idle speed occasionally increases to just below 1500 rpm.

Anyone got any clues?

Thanks
Tricky

[Bob_Roller]

Could possibly be one of two possibilities, first is the centrifugal advance for the ignition timing may be sticking due to lack of lubricant.

Second is the carbs were synchronized on an engine that wasn't up to operating temperature .

[Bengt_Phorqs]

Ditto what Bob said about the centrifugal advance arms sticking.  A well placed shot of oil on them should help.  I had the same problem.  Just remember to ALWAYS DISCONNECT THE BATTERY GROUND CABLE before removing the front cover.  For that matter, disconnect it anytime you even think to work on anything electrical on the bike or you can blow a fuse, or worse the diode board.

[Semper Gumby]

1) Air leaks.  Check the carb hose between the carb and the cylinder head for cracks and the security of the clamps.  Sometimes the clamps squeeze off the hose.  One other possible source of leakes is the throttle buttterfly rod.  The o-rings between it and the carb body get dried out or the hole gets wallered out (technical term).  One way to isolate leaks is to spray something light and volitule on the parts you suspect and see if the RPM picks up (SOMEBODY HELP ME HERE AND TELL WHICH PRODUCT TO USE - I CAN'T REMEMBER).

2) Exhaust valves too tight can cause the RPM to float.  Valve recession rearing its ugly head.

These things in addition to the ones previously mentioned.

This crappy advise worth 2 cents.

Good luck.

[nhmaf]

All the items mentioned above can contribute to this problem, but do check the simplest things first - it is usually (but not always) the simpler things. So, check for air leaks (I use a product called WD-40 here in the USofA to spritz around the rubber intakes - will cause white exhaust smoke if it gets into the combustion chamber in quantity). check valve clearance, and check carb synchronization and idle speed screw settings when the engine is fully warmed up before you dive into the ignition trigger/bean can under the front engine cover.

[scarygary]

I had the same problem as you.. Mine was probably the gaskets for the choke assembly. They were shagged when took apart my carbs.
if your carbs look anything like below.. it is probably an air/fuel leak

[Barry]

Your idle speed may be just set too high. With the choke off it shouldn't idle anywhere near 1000rpm when cold.  At least mine won't.

I had  a similar problem when I first rebuilt my carbs until I learn't to set the idle when the bike was fully warmed up. .....but not before I'd stripped the bean to investigate the "sticking advance mechanism".  We live and learn at least I learnt how the bean can works. Don't go there unless you have to. The bean can advance mechanism is buried behind the points plate and not that easy to get at.

nhmaf has it right try the simple things first.

[montmil]

Small point regarding R65 idle speeds... Prior to 1981, BMW utilized a heavier flywheel than the lightened units installed from 1981 forward.

The idle speed of the 81+ bikes needs to be a little over 1000 rpm (1025-1050) to insure that the timing chain and chain sprockets get sufficient oil.

Yes, you can tune your R65 to idle at a lower rpm but you'll shorten the service life of the timing chain and associated components. This info from raccoon head, aka Snowbum.

My '81 R65's idle is set at 1050, verified with the Vapor digital tach. The 83 is close to the same rpm but I have to listen as I have the OE tach on this scooter -not as accurate.

Monte

[Trickydisco]

Cheers guys, when I service it this weekend I think I will check the valve clearances first because there is a little noise from there, hopefully this will sort it. Just got my hands on a Haynes manual, I think this will become my new bible for a bit.

[Bob_Roller]

Sounds like this is the first BMW airhead you have owned, a noticeable ticking from the valve train, is quite normal, even when the valve clearance is adjusted correctly .

If it's quiet, there is a problem !!!

[Trickydisco]

yepp sure is the first air head I have owned.

[MrRiden]

TD,
Add one of these to your tool kit http://www.powerchutes.com/manometer.asp
It is a good aid in adjusting fully warmed carbs. We were just discussing it here: http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1242493454
do you have a shed or garage to perform work in?
rich

[plc]

Hi All,

Tricky, my '84 LS did exactly the same thing, revs were up after about 20 mins of riding, i.e. fully warmed up.  I checked the advance weights and they were fine.  I was new to Bing Carbs so took it to someone to fix. He retuned the carbs and replaced the inlet manifolds. They were pretty poor quality and the problem is now gone. So the PO had tuned it cold and also had leaky manifolds.

Best wishes,
Paul