First project, 1980 GS550L needs a fair amount of work...

[Aerospaceman]

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Recently picked up my first project-bike! A 1980 GS550L (black), and it came with a 1981 GS550T (red).

Planning on getting the L up and running (roadworthy/safe) and then potentially customizing it in some way (cafe? but I may keep stock and play with the red one instead - but for now just focused on getting it up and on the road as-is).

Current status of the black bike:

• Front brake has no pressure - assuming all the fluid leaked out
• Rear brake may be locked up - wheel spins but with a lot of resistance
• Exhaust has a pretty big hole on the right muffler, otherwise looks in decent shape
• Bike runs, sounds pretty good, but smokes something bad. Pretty sure it's blue but have only ran it in poor light.
• Frame is essentially rust-free, only surface level anywhere I've found (aside from a couple spots on the exhaust)
• Only has 4500 miles, for whatever that's worth on a 41-year-old motorcycle

I am focusing on the engine first, specifically that smoke. Previous owner (shop) picked it up with intent to fix and flip, but smoke led them to cut loss and I picked it up for cheap. I ran a compression test on the cylinders (pulled all plugs and disconnected gas, connected gauge to each cylinder in sequence, open throttle and cranked over until pressure settled). Pressure readings were 106, 115, 90, 115 psi for cylinders 1-4 respectively.

Before I pull the engine out/apart, is there anything else I should check?

This is my first major mechanical project and I have some remote assistance from my brother-mechanic (long distance though).

[Grimly]

Those compression figures might simply be the shims need sorted out, or the ring packs have got stuck (accounting for smoke), but if the smoke is caused by the valve stem seals turning into lumps of carbon, there's not much choice but to take the head off. Then you can re-ring it, if necessary.

I'd do the valve clearances first, plus whatever else it needs to run properly, then see what happens to the compression and smoke after it's done a few hundred miles.
Put some ATF / acetone mix down the plug holes and leave it for a few days, if you're lucky it might free off a few sticky rings.

[Aerospaceman]

Thanks for the suggestions! So you think checking/adjusting valves, then brakes/electronics/exhaust and pack on a few hundred miles as is? What if the valves end up not needing adjusting?