Triumphrat

ydog

Just got a 67 mt cub and it is misfiring at hi rpm. Can anyone give me some direction on how to advance the timing? Thanks

Triton Thrasher

You need to follow the manual and set the timing correctly, rather than randomly advance it in hope of better running. We can't rewrite the manual here for you.

Misfiring at high rpm can be oil on the contact faces of the points. Clean them with paper. Can even be a failed charging system and battery going flat, or fuel starvation, or something up with the notoriously fussy Energy Transfer ignition, if it has that system.

ydog

It does have the energy transfer system. Haven't found a good source for tuneup guidance. Any recommendations? Thanks

ydog

It does have the energy transfer system. Haven't found a good source for tuneup guidance. Any recommendations? Can the ETS be replaced with an electronic ignition system? All new to me. Thanks

Triton Thrasher

Typical ET problems. The alternator sends out little waves of AC current. If the points don't open at a good part of the wave, the spark fails. It is likely that as you rev up, the auto advance is advancing points opening to where they are not getting good power from the alternator. Some ET bikes have the other fault and won't start.

Causes can be too much advance (in your case), points gap too wide, also in your case, tired alternator, alternator rotor mistimed to the crankshaft, worn auto advance, not using the special ET auto advance, not using an ET coil, trying to wire the ignition like normal coil ignition, God knows what else.
Some will disagree, but I think that ignition will always give you trouble.
I see that Googling "Tiger Cub club" and "Tiger Cub spares" brings up useful-looking stuff.

Mr.Pete

It's still possible that you just have a condensor problem.The misfire would be load dependent,and limit your road speed to about 1/2 what it should be.If it's an open-circuit condensor failure (more likely),you can just fit an extra condensor to the coil terminal or points wire.

You may need a degree wheel to check timing and phasing of the ET.You definitely need the ET type AAU,which has a short advance curve (5 camshaft degrees,or 10 degrees at the crankshaft).You might get by using a different AAU,provided you lock it at full advance.

I don't know what the fully advanced timing is for a Cub.With the engine in that position,you should have the points just opening when you twist the AAU to the fully advanced position.
The alternator should then have the leading edge of the magnets on the rotor just level with,or up to 1/16" past the trailing edges of the stator laminations.If you look at the top of the rotor the front magnet edge should be about level with the front stator lamination edge.

There should be holes in the back of the rotor that you can choose to get it phased right at full advance.You can drill more,if necessary.

ydog

Thanks for all the great info. Looks like I have my work cut out for me.