750K1 ignition poops

[budsofnavarone]

Hello Everyone! Long-time listener, first time caller here. Big fan of the show.

So here's my deal. I recently aquired a 71 CB750 on a rigid santee frame that some kid from TN had been piecing together in his backyard for however long. I get the bike and she's good enough to run me all the way home about 25 miles away with no issues, purred like a kitten at stoplights and ran the freeway like a champ. I get her home and park it.

Next day, nothing. Checked the coils with a multimeter, bad on the 1-4 side. Well ok then I got lucky and she had just enough to bring herself home. So... new coils, new plug wires, new plugs, new battery, and new wiring all around. Still nothing. It's gotta be something funky with the points I think. They were pretty grody looking and a little pitty so I filed and smoothed them out then threw them on the engine. She fired... ran smooth for 15 seconds on the first kick and then quit and wouldn't fire again.

So what do ya'll think? It's the points right?


PS I know the bike looks like a evil mess but pardon my dust as she is a work in progress.

[Guest]

Did you replace the condenser? Battery charged up? Idle rpm most times isn't enough to charge a battery. Good gas? Pet cock on and tank full?

[budsofnavarone]

750K1 ignition poops

Did you replace the condenser? Battery charged up? Idle rpm most times isn't enough to charge a battery. Good gas? Pet cock on and tank full?

the battery is newly bought and fully charged, fresh gas, fuel lines, and filter. Petcocks good, carb float bowls fill midway with gas and there is no overflow. The spark plugs show no fouling.

[Guest]

Well, make sure you're getting spark on all cylinders, and then make sure you're getting gas in the cylinders. Use the choke to prime the carbs and get fuel in the head with a few cranks, then pull a plug or two and see if they are wet, if you want you can spray some ether / starter fluid if it fires from that you have fuel delivery issues, so possibly a vacuum leak.

Since you adjusted the points it would be a good idea to make sure the points plate is lined up correctly, for the correct timing... use a clean sheet of paper to drag through the points after filing, or if you have one a popsicle stick works really well for cleaning points. And make sure the point gap is correct... you didn't mention anything about the condenser and bad condenser will cause the heavily pitted points you described, it's always better to replace points than file them... filing is for routine maintenance once they are badly pitted they need to be replaced, the condenser basically stores energy and stabilizes the arc during the continual collapsing electrical field of the points to prevent pitting.

So check the points plate make sure it is where it should be; a timing light will dial it in after it fires and idles. If you have fire and fuel at the cylinders,then most likely the point timing is off.

[budsofnavarone]

bad condenser--> pitted points--> bad1-4 coil

I threw the new points and condensers on and you were right, fired on the first kick. Much appreciation jetblack for responding with the good information. Im gonna assume carrying a spare set from now on maybe a good idea until I upgrade to a pamco. But until then I now know what to keep my eyes on, besides the road.

Thanks man