I decided to revive my 1984 Xr350 after a couple of decades of storage. After cleaning tank, carbs, fresh fuel it fired on fourth kick. Bad news is it produces a smoke screen that kills every mosquito in the neighborhood...I did a Mystery oil soak overnight, ran for about ten minutes. No change, Drained oil and filled with straight 30 + STP type added. Repeat running engine, no change...
I am unable to try a Mexican tune up on an loud, unregistered dirt bike in my community.
Engine was a strong runner, 2 seasons old, lots of XRsOnly internal goodies. Is it possible the 30 year old valve guide seals have disintegrated and causing the oil burning?
Compression seems good, crisp throttle response...
Your rings could be stuck and/or your valve seals could have dried up. A compression check could help in this diagnosis but even then it could be either/or/and. Stuck rings might still have some compression. Best thing to do is take the top end off so that you can inspect the rings, clean the rings if needed and just go ahead and replace those valve seals. If you had access to the Mexican tune-up you could find out if it was just the rings sticking. And by replacing the valve seals you'll take care of the valve adjustment as a part of the process.
Alternately you could just replace the seals through the inspection cover then adjust the valves and see if that takes care of it.
Try Seafoam. I'd pour some in cylinder, let it sit overnight, repeat, put some in the crankcase, and fire it up. It is one of those miracle cures, but you have nothing to lose at this point.
I have seen it work for this sort of thing.
Probably stuck rings. Bad guides and/or seals don't produce a smoke screen worth of burning oil
Your rings might be stuck, or the seals on your valves might have dried out.
Update:
Tried a multi day MM oil soak, ran it until hot but no change in smoking.Changed crankcase oil to straight 30 + an STP like treatment. ran until hot: no change. Seafoam soak........, no change. Bike would start second kick, good compression, sounded crisp.
Guess is that some minor bore corrosion or oil ring failure must be issue Too many other projects that need finishing and short on cash and shop space.
I sold it with full disclosure that it needed rings at minimum and possibly a piston and bore. On to next resurrecting more old forgotten toys. Next , 1989 ATK406 Cross country, 1975 Honda MR50 Elsinore.
Thanks for the suggestions.
