smokey engine-which repair option??

[domiles1]

Got a '79 GS750 which runs a treat but smokes a bit when idling and a fair puff when pulling away. Tried a secondhand engine and it aint much better. Looking at repair options ....
1. Big bore kit, I think its about 810cc, about £500
2. Try replacing just the piston rings, £200
3. Live with it! £0

Was hoping to get the bike as near perfect as possible, a nice reliable machine, but a few unexpected problems are making it cost too much. Any advice on what I could try or any comments on my repair options gratefully received.

Cheers
Dom

[Animal Mother]

Valve guides?

What oil are you using?

[MisterCinders]

Where is the smoke coming from?

Leaks in the exhaust headers? In the head?

Is the smoke from the engine or just oil burning off, possibly indicating an oil leak?

What color is the smoke? Does it smell like fuel?

[Big T]

Test your compression and see if it is within spec - report here

The most likely cause is valve guide seals. These can be replaced with the head in place, there's a guide to it somewhere around here

For the time being, go with the $0 option

How much oil does it use?

[domiles1]

Thanks for the replies, everyone. Lots of questions that need answers! I'm getting the bike back from the workshop next week so I'll have a good look at it and answer some of these questions. The smoke is coming from the exhaust so its like its coming past the piston rings or some other way - valve guide seals possibly.

[SqDancerLynn1]

Pull the top end off. Replace the base gasket, hone the cylinders, replace the rings, replace the valve guide seals..