Engine cut off and won't start

I have had the engine rebuilt on my 850 Commando. I have not ridden it much yet. Yesterday I used it about 20 minutes, easy start and good power, then it cut off and I could not start it. It seemed like no spark. The fuse is good. I checked the spark with plugs out. It looks good. I bypassed the ignition switch, does not start. The red light goes on normal and the battery looks strong. I have a Mikuni carb, all clean. And electronic ignition. I really don't know where to look. Normally with spark and gas, you at least get some explosion. I'm thinking of putting in new plugs, but these are almost new. I need help. François.

gayf said:

I have had the engine rebuilt on my 850 Commando. I have not ridden it much yet. Yesterday I used it about 20 minutes, easy start and good power, then it cut off and I could not start it. It seemed like no spark. The fuse is good. I checked the spark with plugs out. It looks good. I bypassed the ignition switch, does not start. The red light goes on normal and the battery looks strong. I have a Mikuni carb, all clean. And electronic ignition. I really don't know where to look. Normally with spark and gas, you at least get some explosion. I'm thinking of putting in new plugs, but these are almost new. I need help. François.

Click to expand...

Bad gas?
Bad Spark Plugs?

Verify gas flow to carb---are the plugs wet after trying to start?
Verify your battery is fully charged. Check connections.
Verify the timing---may have slipped if not tightened down after initial timing was set.
Retime just to verify.
You claim plugs are getting spark> how much?
If just rebuilt--I am presuming the compression is ok.
If all this checks out ok---perhaps your electronic ignition controller went "POOF". Which system is installed?

Stay tuned for additional suggestions from other forum members.

Do the easy things first. Check for voltage at the coils with ignition on or hot wired. Pull the plugs and check for spark, it's easy when the plugs are out. Kill switch OK? Check for fuel with tickle and fuel flow from petcocks. Then go on to the timing and other issues.

Dave
69S

All ignition power goes through the cutout button on the right handlebar. It's a points-type switch, not self-cleaning and normally closed. I measured a .3-to-.4-volt drop through that switch and that was not under a load circumstance. That is, the switch may pass sufficient current when cold, but, being resistive, it heats up and increases resistance and the bike shuts off after running a while.

I'm still in the midst of trouble-shooting my own spark trouble. I wired switched power (white) directly to the ignition system feed (white/blue, I think--I don't have the bike or diagram in front of me). I should have load tested the circuit with a headlight or something, but I just decided to wire around the cutout button. All the wires are right there at the main frame tube where that big block of connectors is.

I made a short jump wire from 28-strand with Lucas bullets. LIke I said, I picked up .3/.4 volts (12.3 vs. 12.6-12.7) at my electronic ignition module. The tank is not back on so I have not tested it, but I'm hoping for the best.

I don't think the wiring is very different over the years, but for clarity my bike is a '74 850 Roadster.
Mark

Thank you all for the tips. I have noticed that my coils were 12v and that the ballast was connected. I changed the coils to 6v and reconnected. I have spark at both plugs. I tried new plugs. I checked the timing statically, spark happens at top of piston compression cycle. I managed to start the bike but it was running very badly. Very hard to start. When I pull the plugs, they are wet. The gas is fresh and spark plugs new NGK BPR7ES. Still working on it.

PROBLEM SOLVED.

IN MY MIND I WAS SURE IT WAS AN ELECTRICAL PROBLEM.

IT WAS A CARB ISSUE. I HAD CLEANED MY MIKUNI AND I DID A BAD JOB AT SCREWING BACK IN THE PILOT JET. I FOUND IT AT THE BOTTOM OF THE BOWL. SO WHAT HAPPENED WAS THAT IT WAS FLOODING AND SO ON.
THANK YOU ALL FOR YOUR INPUT

FRANCOIS

NORTON COMMANDO COMBAT 72
NORTON COMMANDO 850 73
BSA FIREBIRD 69

Did you re-connect the ballast resister I don't think you need them with electronic ignition.

Yes I did reconnect the ballast resistor. The electronic ignition we use are made by some member of our club and he recommends to do so. I could try without, is there any advantage?

François