Topic: No spark on 1 and 3

[robd1017]

My 1974 CB750 has been sitting for two weeks while I painted the headlight bucket and controls.  I had a heck of a time getting it to start today and once it did, it didn't sound right.  I shut off the engine and on a hunch I felt the exhaust and pipes 1 and 3 weren't hot.  I pulled the spark plugs and checked for a spark and of course 1 and 3 had no spark.  It seems like a coil has gone bad, but I'm not sure how that happened since the bike was just sitting in my garage.  But before I buy another coil, is there anything else that could be causing this problem?

Thanks,

Rob

[Calflash]

Do you have power TO the coil? Check your connections. If they are good, swap coils and see what happens.

[Markcb750]

1 & 3 are separate coils, ar you sure it is not 1 & 4 (the outer pipes) or 2 & 3 (the inner pipes).

when did you perform your last 3000mi tune up?

[2wheels]

how's the point gaps?

[Stev-o]

Check your spark plug caps with an ohmmeter, mine went bad.

And give it a full "3000 mile" tune up.

[nancy]

My caps too. I had 3 showing 5ohms and 1 showing 9.75. Should all be around 5ohms. Higher the number means the WORSE they are.

[MoMo]

Have you made sure the caps are screwed tightly to the wires? Frequently  I need to trim the wire back a bit and then rescrew the cap back on. Good luck, Larry

[Spanner 1]

OP... couple of Q's... .. were the #1 and #3 plugs wet or dry when you took them out and how did you test for spark?,,,,, I think 1 and 3 float needles are stuck and dry bowls...... put bike on mainstand, turn-on gas, tap each float bowl with a screwdriver handle, wait 30 seconds, then try to start bike. Stuck floats/needles can be common esp. if the bike is left on it's sidestand IMO.