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RT Caldwell 01-28-2013 06:31 AM

Resurrecting a /5 BMW
Hi y'all,

Newish member, first post, nice to be here.

After a 4-year hiatus, I've dug my '71 BMW out of the pile in back of the shop and have it once again running a bit. It starts right up, idles relatively smoothly and accelerates well. Problem is, when it settles in at a steady RPM with no positive throttle applied, it misses and runs very rough. What I mean by no positive throttle is that it runs smoothly going uphill. I've cleaned and gapped the points, set the timing and checked the wires, plugs, etc. Before parking it, I'd replaced the twin coils with a single Harley-type coil with a 3-ohm rating. Carbs are new 34mm Mikunis, so I doubt this is a fueling issue, it feels very strongly like ignition.

The only thing I can think of is maybe the centrifugal advance unit, so I have some new springs on the way. Any other ideas or thoughts would be greatly appreciated.

Again, it's good to be here,and thanks in advance for your wisdom and advice.

RT Caldwell 01-28-2013 06:37 AM

Damn, wrong parking lot. Thought this was Airheads - sorry gents.

bpeckm 01-28-2013 09:24 AM

My first thought was carbs, but you could be right on the ignition advance unit... maybe it's sticking too advanced, but I'm not sure that it would make it run "rough"... more likely it would ping or something? .......does it come back to idle when you blip the throttle? a lot of times a sticking advance will keep the idle speed up 'way high.

....and keep after the carbies, too.... I don't know Mikunis particularly, but the transition from idle/pilot/running jets can get lumpy if one of the jets is partially blocked etc...

Good luck!


Mista Vern 01-28-2013 01:32 PM

Hope this gets moved to airheads, but welcome anyway! Check too for vacuum leaks at teh carbs. Best of luck!

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