1981 Z50R issues - weak spark

[rgriggs]

Hi, I have a 1981 Z50R that my dad bought at a yard sale years ago. I rode it as a kid, then when I outgrew it, we parked it in our storage garage.

Now, about 25 years later, I'm hoping my kids can enjoy this bike as much as I did. We pulled it out of storage, put in some fresh gas, checked the oil, and gave it a couple kicks. It actually started! However, it required full choke to run.

I cleaned the carb carefully and tried again - still required full choke to run at all, and died often. I adjusted the jets, etc.

After a bit more tinkering it completely stopped and wouldn't hit, even with ether.

Checking the spark plug, the spark was very weak and sporadic. So I got a new spark plug and the spark was still very weak and it wouldn't hit.

I did all the following to no avail:

• Checked the points gap (about 0.012)
• Cleaned the points with emery cloth
• Removed the flywheel and tested continuity on all wires, as well as verifying that the run/stop switch works properly.
• Tested continuity of primary and secondary ignition coils
• Ensured the points were not stuck and work properly

Finally I removed the spark plug cap and held the bare wire near the frame. I got a very strong bright blue spark. I replaced the spark plug cap and tested again with the spark plug. I was now getting a strong spark at the plug.

Replacing the plug, I cranked the engine and it started (carb needs adjusting).

However it ran for just a couple minutes before dying and again the spark is very weak. Even removing the spark plug cap and testing the bare wire yields a weak/sporadic spark again. Won't even hit on ether.

Any ideas? Would it be best to replace the condenser? Or does this sound like an ignition coil issue?

The ignition coil spark winding measures 5k ohms with spark plug cap removed, and 10k ohms with cap installed.

I'd appreciate any suggestions on how to troubleshoot/fix this and get this great bike running again.

Also, anything else I should check/repair/replace to help avoid injury and/or damage to the bike after having been in storage for 25 years?

Thanks!

 

[hrc200x]

Where the points rub on the flywheel, was that area still nice clean metal or rusty? If its rusty it can wear down the rub block on the points fast, which sets them out of adjustment. Did you emery the points first then adjust the gap or the other way around? Since you had a good spark after cutting the end off the plug wire and moving the wire around is there a chance the wire is damaged further up the line or where it goes into the coil? I'd keep messing with the points and make sure they are in the .012 to .016 range, try setting them at both the top and bottom of the range. Fuel systems in bikes that sit usually are dirty and need attention, that means starting at the gas tank and working your way down to the carb. Petcocks, fuel filters, gas lines, carb openings and jets can all plug with old gas, rust, corrosion. Next to the main jet should be a pilot jet with a small opening, from the diagram it doesn't appear its removable, did you try to put a small wire through that? Is the hole in the main jet open? The main jet looks like it threads into a main jet holder that has a bunch of small holes in the side of it that also need to be clean.

As for other things to do to bike, oil change, adjust the valves, clutch adjust, cam chain adjust, check air filter, these small motors seem like they need a air filter in place in order to run correctly and most importantly to keep dirt out of motor. Sometimes running with the choke on is either compensating for a plugged jet or a intake leek between the carb and motor. Not familiar with a 79 Z but there might be a few different gaskets or o rings between the carb and head, make sure they are all intact and there is no metal to metal contact, have seen some where they had the gasket against a o ring which left it metal to metal on the other side. If you get good spark and bike running, ways to check for intake leaks is to use starting fluid and spray it around the intake pipe where there are o rings or gaskets and see if rpm changes, depending on how bad the leak is seems like it can either make rpm go up or down. But keep in mind your spraying something flammable next to the spark plug wire, maybe cover it up with a doubled up rag or spray from the right side of motor to left. Also if motor stalls or kicking it over you hear a squeak this can also be a intake leak.