Topic: 72 CB100 engine issues?

[JWorsech]

I picked up a running CB100 a few years ago, It needed a little work so i put new points, ignition coil, cleaned the carb. I set the timing and got it running again for a few days, albiet not running entirely smoothly. Then it just stopped running all together. No amount of starting fluid was firing it up, not even a pop from the engine. A friend of mine helped me go over everything and could not figure out why it wouldn't run. So we did a compression test on the engine and found that it was only getting to 120PSI after a dozen and a half kicks. I saw in the manual it should be at 170PSI. So any help in figure out what to do next to get this little bike up and running would be very welcome.

[MauiK3]

Sounds as if you have an ignition issue, it should run at 120 psi, which will likely improve if it is run some more.
Check all the wiring and see if you have spark with the plug removed.

[HondaMan]

By chance, did you also replace the condensor with the points? If so, re-install the old condensor. They don't ever wear out from use, and most new ones are coming from China and are JUNK right from their packages.

[PeWe]

Compression test with wide open throttle?
If not, lower value.

[WhyNot2]

Need to have a fully charged battery as well.

[Ozzybud]

Are you getting a spark?  Check for a fouled plug. Easy stuff first.

[JWorsech]

Sounds as if you have an ignition issue, it should run at 120 psi, which will likely improve if it is run some more.
Check all the wiring and see if you have spark with the plug removed.

Wiring all seems good, and it does get a spark

[JWorsech]

By chance, did you also replace the condensor with the points? If so, re-install the old condensor. They don't ever wear out from use, and most new ones are coming from China and are JUNK right from their packages.

I did not replace the condensor, just the points, spark plug, and ignition coil as far as electrical goes.

[JWorsech]

Need to have a fully charged battery as well.

Got a new fully charged battery on it as well.

[low-side]

If I recall correctly, those can jump several teeth on the cam sprocket when the cam chain is loose.  Might be something to check into if fuel and ignition are good.

[carnivorous chicken]

Spark first, that's easy. Blocked jet too. It'll run on 120 and might go up some.

[HondaMan]

Maybe check this, among the other things you're doing: there are 2 paper gaskets where the intake manifold bolts to the head and that plastic insulator. Often, they are deteriorated, and leak. I've made some with scissors and a hole hole before, out of generic gasket paper from the local auto parts store.

There is also the possibility that the gas in the tank is "wet" from sitting: it absorbs moisture from the air and inerts the gasoline in about 30-60 days, depending on where you live. This will make the bike REALLY hard to start, if it will at all.

[MauiK3]

We can get ethanol free fuel here, 89 octane. When I had my Ruckus (49cc) the difference was noticeable. It really ran better on it. The small extra energy available due to no ethanol made a difference. I don't think it cared about the octane number since it was water cooled and didn't have any knock problems.