Restoring old '78 YZ-80

[DarylS]

Hi All,

By hook, crook, and otherwise I managed to hang onto my first ever bike. It's a 1978 YZ-80 that I bought brand new when I was 12. After spending 20+ years hiding in the garage I pulled the bike out of hibernation, put some gas/oil in the tank and after about 20 kicks it fired up, beautiful! My 9-year old son is now anxious to try "Dad's old bike" out for himself. It will make a great restoration project.

There's some obvious parts the bike needs (tires, chain & sprockets, brake pads, rear swingarm bushing etc.) but need some advice from the group, hence this posting.

I put the bike away properly way back when I stored it (drained tank & float bowl, fogged the cylinder through the spark plug hole etc). that's why it started OK for me.

I did say I fired it up, but the idle isn't stable. It starts up fine but the revs never "drop" when you lift off the throttle. So if you blip the throttle to say 5000 RPM the engine STAYS at 5000 RPM till you hit the kill switch. When you restart it the revs are normal until you rev the engine again. What's really weird is that if you press the kill switch only long enough till the revs drop, then flick the switch back over before the engine stops the engine will maintain the revs at whatever speed the engine was spinning when the spark came back on.

Any idea's what the problem could be?

TIA!

Daryl

[Airhead]

Hi Daryl, If the inlet manifold is rubber, it sounds like it's split or loose. to prove this spray liberally with something like WD40 when the engine is racing, If it's split or loose the revs will no doubt change.

...Paul

[DarylS]

Hi Paul,

Thanks for the advice.

It IS a rubber Inlet Manifold so I took the carb off today to get a good look, the inlet manifold seemed fine. On re-assembly I used silicone grease to help seal the carb-to-manifold junction in case there was a flaw that I didn't see. Unfortunately I have the same behaviour. The "WD40 trick" didn't work either. The only way to reduce revs is to use the kill switch as before.

Any suggestions what else I can look into?

Is there anything in the carb itself that could be stuck or clogged? I haven't taken it apart yet but am thinking on giving it a good deep clean to see if that will fix the problem. Also, with 20+ years of storage there may be some internal seals and such that may have dried out. Wish me luck finding parts if that's the case!

Cheers,

Daryl