Poor or inconsistent idle when warmed up. Sometimes, it will drop and idle smooth at 800-900 rpm. Sometimes, it feels a bit rough.
stock carbs with stock jets. mixture screws out 1 1/2 turns.
Valves are set at '.004" intake, .008" exhaust
Points contacts are clean and nearly spotless (I've had a Dyna Ignition booster installed for a couple years now)
Points gap, .016"
Timing is set at the upper horizontal mark on the flywheel
Just wondering what else could effect idle?
Condenser failing? I can measure it on my Fluke meter and it charges and dis-charges normally (set to resistance)
Plug wires and caps?
A new condenser might be good to try. Measure the resistance from spark plug cap to plug cap...should be around 20-22K ohms. Are the coil towers clean and free of corrosion?
Might have an air leak somewhere. Try spraying each carb with some brake cleaner and see if the idle speed changes when it sucks in some combustible fluid.
'78 R100/7 '69 R69S '52 R25/2
I tend to think ignition since the bike wouldn't idle at all last fall, while on a trip. In that instance, I messed around with the idle screws with very little change in running. I then pulled the front cover to see the points had closed down to about .004".
Set them to .016" and idle was restored.
Rode another 1,000 miles or so since then so I'll check the points gap again and verify the condenser is good.
Opening up the intakes to .006" sounds like a plan too.
As I said, the ignition system is mostly stock with a Dyna green 2 plug coil in place of the stock Bosch 6v units. I have stock wires and end caps that I believe measure out to around 1.2k, but I'll confirm.
And I added a Dyna Ignition Booster a few years ago, which I think mainly serves to prevent increase points life.
btw, stock Dellorto's, stock jets and mixture screws 1-1/2 turns out from stop. Timing set at upper horizontal bar on flywheel.
I'm taking measurements with a micrometer to determine if something's worn or not. Camshaft tip has zero runout and the "D" section of the advance mech meshes tight and true to the cam.
All that being said, I'm kinda, sorta, maybe leaning to installing a Alpha ignition system. I know it's blasphemy and I'm a points and condenser guy, (even have and still use my old dwellmeter), but I love riding this bike high miles and constant ignition problems AND possible replacement of a very expensive stock advance mech have me taking a huge lead off of first base.
your thoughts are appreciated.
My '74 R90s started having points gap issues a couple years ago. Always a fan of the original points and condenser (and I still used my old dwell meter on occasion...), I was reluctant to switch them out to electronic. Years ago I had a bad experience with a Dyna III system, so I wanted to keep it stock if possible.
My advance mech and points cam were showing wear and tear after 140k, so I picked up a unit from Rick Jones (Motorrad Elektrik).
Installation was extremely simple. About the only thing that took extra time was figuring out the best way to mount the module (underneath the gas tank rubber posts, under the frame), and setting the timing.
Once that was done, I buttoned it all up and took a 50 mile test ride.
Immediate improvement in starting, and idle smoothness.
I've been riding the S to work the past couple weeks (120 mile commute) to Lansing, MI, and the bike is a pleasure to ride again. The motor feels fresh, idle is very, very smooth and consistent.
And unlike the Dana III system, the advance unit isn't used, as the advance curve is done electronically.
So far, I like it very much.