Replaced plugs but now getting smoke?

[robgusto]

I have a 1981 GS 750 and fired the bike up today. I recently purchased the bike and am still new to riding/wrenching. When I felt the header and pipe for the 3rd pipe in from left it was cold when all others were hot. So I started troubleshooting by replaced the plugs. The bike came with NGK R DPR7EA 9 plugs. I replaced with recommended NGK 2120 D8EA plugs. I noticed that there was a slightly above normal amount of smoke out of the right side pipe (3rd and 4th pipes/wires/cylinder) but all 4 pipes were hot, so I'm not down a cylinder!! Good news!!!. Do I need to gap the plugs or do they come spec to fit the bike? Any ideas on where to start troubleshooting the issue with excess smoke? Also, previous plugs looked good when I took them out.

[tkent02]

You are probably just burning off the unburnt fuel from the cold cylinder that has been accumulating in the pipes. Go for a ride.
NGKs new in the box are usually gapped pretty close. Don't worry about that either if you don't have the correct gauge for it, as long as it runs well...

[Nessism]

That one cylinder is most likely burning oil, and the oil fouled the plug. Now that the plug is firing it shows the oil burning smoke. I'd do a compression check: warm engine, hold throttle wide open, and take compression.

[robgusto]

thanks for the response I will go for a ride to see if I can clear it out

[castlekin]

strange as it may be, check the color and smell of your smoke. That will tell you if it's a fuel or oil issue. Dark smoke, burnt oil smell is oil. Gray smoke, gassy smell is fuel.