sudden smokey cylender

[jimho london]

hello ,just joined this site  .my wife has had her 400/4 for 15 years problem free , last year i bought a 1975  k5 american import ,original and running good, i didnt use it much and it stood unused for a few months ,  i started it up and got much smoke from the breather then smoking badly from one pipe,being used to old brit twins and singles i am a bit scared to start tearing it apart .any ideas on if it can be something a bit more simple than rings and pistons,i,m frightened to give it a blast in case i make things worst,hope someone can help , many thanks ,  jim.

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Welcome to the forum. I would do a compression check to find out if it is the rings, or valves.
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[sgtslag]

If it sat for a few months, without being run, I would check to see if you have bad gas, varnish deposits, or even water in your gas, or oil.  Why not start with the simple things, first?  Get some SeaFoam, or similar gas additive which will absorb water, and dissolve varnish deposits within the fuel system.  I would also check the oil to see if it is contaminated with water (has milky white stuff in it); again, if you can get SeaFoam, follow directions, and add it to the crankcase (will absorb water, dissolve varnish and carbon deposits within the engine and the transmission -- change the oil and filter as soon as it darkens; usually it will turn black within minutes, if the engine has never been treated before).  If you can't get SeaFoam, run the engine until the oil gets to above 212 F/100 C, to ensure it will boil off any water within it.  Be careful not to let the engine idle too long, as you never want the oil to go above 250 F...

If none of that helps, then go for the compression check, and beyond.  Cheers!

[Re-run]

Welcome!
Now, to the grease.
If the bike sat for a while, as slag said, it could be bad fuel.
Condensation also can build up and when the engine fires, it burns off the water.
You could have a sticky valve or a ring was stuck and even though it is free, the cylinder wall may still have a little build up that will wear away.

I guess it depends on what color this smoke is.
get in sunlight so you can accurately see the color.
White = water
black = fuel
blue = oil

Look carefully as the black and blue can be hard to tell apart.

[jimho london]

thanks for your reply,s.  i will do a compression test first  as advised ,hopefully its a sticky ring or valve as mentioned , i always think the worst first (maybe i need to speak to someone),i tend to think its not bad fuel as i,v had bikes sitting for a long time without a problem and it was new fuel last time i had it on the road ...........but who knows it could well be that prob. thanks again.

[jimho london]

thanks for your reply ......a comp test it is , fingers crossed its something sticking, cheers