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RickR90s
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Farmington Hills, MI
Joined: 11/28/2016
Posts: 73

'74 R90s with stock Dellorto's, stock ignition system (points and condenser)

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?

Thanks,

Rick

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RickR90s

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6845
I guess it's either carbs or

I guess it's either carbs or ignition? That's helpful!! Not that it will help anything, but I'd run the intake clearance at 0.006"...this is what BMW settled on after many years...doesn't hurt anything really, just lets the valve sit on the seat a bit longer and cool down some more.

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.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

RickR90s
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Farmington Hills, MI
Joined: 11/28/2016
Posts: 73
Idle

Thanks Schrader for the info.
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.

Thanks again,

RickR90s

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RickR90s

RickR90s
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Farmington Hills, MI
Joined: 11/28/2016
Posts: 73
Idle

I'm finding inconsistent points gap measurements each time I measure, when rotating the engine. (140k on stock mechanical advance)

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.

RickR90s

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RickR90s

skychs
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VBMWMO #9221
Joined: 11/25/2016
Posts: 339
Ignition

I have an electronic ignition in mine and love it. Motorrad Elektrik. Installed in 2003. Runs like a charm and has never given me any issues. No one will notice it unless they look up under the tank or inside the front cover.

RickR90s
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Farmington Hills, MI
Joined: 11/28/2016
Posts: 73
Alpha Ignition

Month long review on the Alpha electronic ignition I installed in my R90s.

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.

RickR90s

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skychs
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VBMWMO #9221
Joined: 11/25/2016
Posts: 339
Ignition

Great to hear. I really think it helps any bike. No issues in my R90S. I even installed a Charlies Ignition into my 1967 Honda CL77 Scrambler. It usually starts right up and runs better than ever. Enjoy !!

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