Checking dwell and timing ?

[Bonneybear]

If I wanted to ck dwell, do I hook to the neg of the coil ? which coil ?  To ck timing which cylinder is #1 L or R ?

[Ed Miller]

What year is your bike?  Like, points or electronic ignition?

Either way, don't worry too much about dwell.  The most important check is your ignition timing at full advance.  On all the BMW twins I know of both cylinders fire at the same time (though not on the same stroke of the cycle) so you should get the same timing on either cylinder.

Good luck,

[Bonneybear]

Your kidding, thats crazy, 2 sparks in one complete cycle ?  . Its 1980  w/ points........Thanks

[nhmaf]

Yes, unless you happen to have an earlier model Dyna ignition conversion, the ignition system is
a wasted spark setup, so one cylinder is basically coming on an exhaust stroke while the other
is filling with combustibles.   The early Dyna conversions are long since NLA, so chances are
good that you have the same basic setup.   I usually use the left cylinder (clutch lever side)
because that is where the timing hole is to inspect the timing on the flywheel, but if you
have long enough wires on your timing light, I suppose it doesn't really matter.

[Bob_Roller]

I think it's been about 27 years since I replaced points in an  ignition system. Refresh my memory, is dwell the amount of degrees of distributor rotation, that the points are in contact with each other ?

[Bonneybear]

Yes, dwell is the amount of time that the points are closed.

[Jon_P]

dwell is really when the points close to send a spark, you can advance or retard the dwell. there are alot of ways of doing it, i like to use the dwell setting on my vo meter and set it to the dwell angle which is when looking at the fly wheel is when they fire on the fly wheel degrees.

[Ed Miller]

Your kidding, thats crazy, 2 sparks in one complete cycle ?  . Its 1980  w/ points........Thanks

After 20 years of tuning my dual point Triumph I'm not convinced it's crazy.  Just the price I pay to own a hot rod, I guess.

Some of the high performance Mopar engines had dual points, but luckily not the one in my mom's car.

[Semper Gumby]

Just make sure the point gap is .016" when the cam lobe is at the highest point and then set the timing.  That will get you the right dwell.  I've never seen a number published  for dwell on the R65 or how to read it on a meter (4cyl or 8cylinder scale?)

Got the omega ignition now - I don't worry about dwell anymore.

TTFN,

[Ed Miller]

It's been discussed on either the Airlist or Boxerworks, but since I have E.I. I paid little attention.  It seems like it's in the ball park of 72 degrees, but I can't remember how you convert the 4 cylinder reading to 2.  Probably either double it or half it.  :-)

Snowbum probably says something about it.

[Bob_Roller]

The BMW shop manual that I have, states a dwell angle of 120 degrees at 1000 rpm.

[Bonneybear]

Yeah, my book says, 120 deg. also. I may try it this weekend. For dwell affects timing, timing affects carburetion. I have some carb parts coming today. The only thing I have not taken apart in the past has been the choke assembly, Anything I should look for ??

[Jon_P]

timing does not affect the carburetion. you clean your carbs, torque the heads, set the valves, set your carbs. timing does effect when the air/fuel mixture is ignited to relation position of the piston and valves. setting the dwell is simple as long as your follow what your manual has laid out for you. if you try to do anything different it will run but it run rough in a certian points as you need it to advance as you drive.