1979 KZ650C White Smoke and oil from Exhaust?

Hey everybody looking for some help! I have a 1979 KZ650C that I bought used and I am in the process of rebuilding. I have replaced the head because the valve seats were rusted and beyond repair. I have also bench synced the carbs and replaced many gaskets and O-rings as well as the plugs. When I had the head of I checked the rings and they seemed to be good. It has recently started to blow white smoke from the exhaust that gets worse as your roll the throttle. It also blows out little black specks with the white exhaust smoke but I can't tell if it is oil or just carbon from inside the exhaust pipes getting wet and blowing out. The shite smoke stops once it gets really warm and after you've giving it a lot of throttle wide open. Sometimes it will start again randomly. It also seems to run rich but in low gear on the throttle (up a hill for example) it misses. Looking for advice, help, anything to get this figured out. Also, if anyone knows of a good vintage motorcycle mechanic in the Longview, WA area let me know. Thanks!

Cjyeck wrote: Hey everybody looking for some help! I have a 1979 KZ650C that I bought used and I am in the process of rebuilding. I have replaced the head because the valve seats were rusted and beyond repair. I have also bench synced the carbs and replaced many gaskets and O-rings as well as the plugs. When I had the head of I checked the rings and they seemed to be good. It has recently started to blow white smoke from the exhaust that gets worse as your roll the throttle. It also blows out little black specks with the white exhaust smoke but I can't tell if it is oil or just carbon from inside the exhaust pipes getting wet and blowing out. The shite smoke stops once it gets really warm and after you've giving it a lot of throttle wide open. Sometimes it will start again randomly. It also seems to run rich but in low gear on the throttle (up a hill for example) it misses. Looking for advice, help, anything to get this figured out. Also, if anyone knows of a good vintage motorcycle mechanic in the Longview, WA area let me know. Thanks!

First of all, Im a bit jealous because ive always wanted a black bike. I have the same bike you have in green and blue but 1977.

Anyhow, you have a oil leak within the engine. White smoke is not a good sign, I wouldnt ride the bike until you find out where this leaking oil exists within the engine.

Did you replace the valve guide seals?
Steve

Before you do anything drastic make sure you know what is coming out of the exhaust.
White smoke is condensation.
Blue smoke is oil.
Black is un-burnt fuel.
The little black specs will be just some crap from inside the exhaust.
Establish what colour smoke you have then go from there,
If you did not replace the valve stem seals on the replacement head the chances of oil being burnt is high as the seals will be about 40 years old, hopefully a lesson can be learnt from this, also replace valve stem seals with viton ones from a performance parts specialist they do not harden like others .

Thank you all for the replies. I did not replace the seals when I put on the new head. I am fairly new to motorcycle mechanicing and I don’t have all the necessary tools to do a job like that. When I bought it online the seller said it did not have any issues, guess this is what I get for taking their word. I was kinda leaning toward the valves as an issue but wanted to get some advice. The one positive about this is I was gonna have the seals in the old head done by a guy where I live, that’s how I found out the valve seats where shot. He will bead blast the head and replace all the seals for $150.00 all you have to do is remove it and take it in. Guess I will be tearing it down again. At least I’ve done it once already, just time consuming and meticulous work as I’m sure most of you know.

The smoke coming out only comes out of one exhaust pipe (original dual exhaust). It definitely looks white but smells like burning oil. It also has a fuel smell but if the valve seals are bad I assume some fuel could be making it past the valves?

650 Dude, don’t be too jealous the bike was originally blue and gold (see attached) and I stripped it all down and rattle canned it matte black! I like the look as opposed to being shiny.