Topic: '72 cb500 2&3 cyl not firing, voltage at points, help?

[cb500 maniac]

cylinders 2 and 3 just quit firing on my honda, i checked voltage at the breaker points and i've got power there, it's just not getting to the plugs, how do i check my ignition coils? or what else could this be?

[ieism]

I had a similar problem a few weeks ago. Checking your coils yourself is difficult. The guy that checked mine had a special machine for it. i think it takes a bikeshop 5 minutes, so it will be cheap.
On my bike i've checked the ignition timing, the coils, the plug wires and caps, and it turned out to be a loose or broken wire between the ignition and the coils.
Oh, here's a link to a tread I started: http://www.sohc4.us/forums/index.php?topic=10838.0

[StevieMac]

Are you getting power TO the coils?

[cmorgan47]

you can check for continuity across the spark plug wires(jam a probe into the 2 and 3 wire)--should get some resistance and continuity.
same thing with the inputs.

have you checked the point gaps?
and that the points are in decent shape?

[cb500 maniac]

ok, my problem is evolving. now i have no voltage at the breaker points, i reversed the yellow and blue wires coming from the points condenser to the coils, and got spark on 2 and 3 but not 1 and 4. i have continuity on the wire from the 2+3 points to the coil. i have voltage at both black wires with white stripes going into the coil. my points are definitly opening and closing. im thinking maybe one of the silver cans on the condenser is bad? I have a wealth of mechanical aptitude and talent, but my skills in the electrical department are lacking, i'd really like to get my bike back on the road, cuz there's only about another good solid month of riding season here in rusty akron ohio. i will personally sing hosanas to the name of the person that solves my problem. 

[TwoTired]

Meter probes black and Red right?
 Use voltage scale.  Turn on ignition; kill switch in the RUN position.
Black lead on the breaker plate.
Verify Blk/White to the coils have 12V
Reconnect Blk/White to the coils.
Verify Yellow wire from coil (wire to points disconnected) has 12V. If missing voltage replace coil.
Verify Blue wire from coil (wire to points disconnected) has 12V. If missing voltage replace coil.
Stick thin balsa or thin card board between both point contacts, both points
Reconnect yellow and blue wires to points.
Verify 12 v at stud terminal of both points.
If 12 v missing, disconnect condenser and wire from points stud.
Verify 12 v at disconnected wire end Yellow and Blue.  If either missing voltage find break in wire between coil and points.
Reconnect only the wires to the points stud.
Verify 12 v at stud terminal of both points.  If either missing voltage replace that points set.
Reconnect condenser to the points stud.
Verify 12 v at stud terminal of both points.  If either missing voltage replace the condenser.
Remove card board between points.
Verify 12 v at stud terminal of both points when open. And zero V at stud terminal of both points when contacts are closed. 

Run bike.

Cheers,
 

[750goes]

start singing those hosey whatseys to TT....

he's always right, but never wrong - who would argue with the guru...

[cb500 maniac]

I used the K.I.S.S. (keep it simple, stupid) method, found that my yellow wire had continuity all over the bike, followed it from the condenser and found that when i put a new clutch in last week, i routed the wire too close to the kick starter during re-assembly and the kicker wore the insulation off of the wire and it grounded out on the frame. 2 minutes and some electrical tape and i was on the road again, but i still went over my entire ignition system and found that i have a lot of sparking going on at my points while the motor is running....i figure some sparking is normal, but i've got lightening bolts coming out of this thing, so it's back to my sister's to peel more parts off of her boyfriend's junk 500. i figure i'll just take the whole condensor plate, assuming the points on it are not as worn as they are on mine. anyway extra special thanks to two tired for knowing EVERYTHING. we could use you in the garage with this hacked up 750 we're working on.....some dumbass ripped all the wiring out of it and cut the back half of the frame all up to drop the seat pan, then replaced the rear shocks with solid steel struts for that hip hard tale chopper look......i tried to tell him that he'll not only be able to run over a dime and tell if it's heads or tails, but also be able to die painfully when the remaining 2 frame rails break under the stress of not having a full rear frame or any suspension what so ever. redneck bike building is darwinism at it's finest!

[SteveD CB500F]

The points shouldn't spark - the condensor(s) are toast.  The sparking will wear down the points very quickly (which is why we have condensors)