Kawasaki Ninja ZX Forum banner
1 - 6 of 6 Posts

·
Registered
Joined
·
14 Posts
Discussion Starter · #1 ·
Lately I have noticed that if I let off the throttle quickly a decent amount of blue smoke comes out of the exhaust. If I roll off the throttle, no blue smoke. Some times just a bit of blue smoke will come out if I hammer the throttle from idle. The most prevalent amount of smoke however is on the quick deceleration first described.

Bike has fresh 93 octane gas plus some octane booster, fresh oil change and proper oil fill level.

What are some causes of this? I was thinking about swapping out the spark plugs. I am not sure how involved of a job that is, but I am trying to sell the bike and don't want to waste any un-needed time working on the bike. The few test rides I have had on it have noticed and commented on the blue smoke making them wary and ultimately leading to a lower offer than I would like to accept or making no offer at all.

Thanks in advance for any tips or suggestions.

Bike is a '99 ZX-7R. 22k on chassis, supposedly ~5k on rebuilt performance motor.
 

·
7777
Joined
·
6,859 Posts
Blue smoke is oil. Sometimes a performance motor will have a lot of crankcase pressure and push oil up the breather hose. Disconnect the breather hose from the airbox and plug the hole in the airbox and test it.

Another idea is how full is your oil in the crankcase. There is a sight glass on the side of the cases. It should be half way up the glass. Too full and you dip the piston in oil.

Blue smoke on acceleration is usually rings, blue smoke on deceleration is usually valve guides.
 

·
Administrator
Joined
·
58,646 Posts
Lately I have noticed that if I let off the throttle quickly a decent amount of blue smoke comes out of the exhaust. If I roll off the throttle, no blue smoke. Some times just a bit of blue smoke will come out if I hammer the throttle from idle. The most prevalent amount of smoke however is on the quick deceleration first described.

Bike has fresh 93 octane gas plus some octane booster, fresh oil change and proper oil fill level.

What are some causes of this? I was thinking about swapping out the spark plugs. I am not sure how involved of a job that is, but I am trying to sell the bike and don't want to waste any un-needed time working on the bike. The few test rides I have had on it have noticed and commented on the blue smoke making them wary and ultimately leading to a lower offer than I would like to accept or making no offer at all.

Thanks in advance for any tips or suggestions.

Bike is a '99 ZX-7R. 22k on chassis, supposedly ~5k on rebuilt performance motor.
This would further verify my diagnosis.
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #5 ·
Most likely valve guides or seals are worn. When you let off throttle abruptly there is a high amount of vacuum in the intake and the first thing that gets drawn into the intake is oil from the valve train.
Ok that sounds like a good explaination and probable cause, thank you sir!

Blue smoke is oil. Sometimes a performance motor will have a lot of crankcase pressure and push oil up the breather hose. Disconnect the breather hose from the airbox and plug the hole in the airbox and test it.

Another idea is how full is your oil in the crankcase. There is a sight glass on the side of the cases. It should be half way up the glass. Too full and you dip the piston in oil.

Blue smoke on acceleration is usually rings, blue smoke on deceleration is usually valve guides.
I will try your first suggestion when I get home, thank you. The sight glass right now is reading about 3/4 the way up, is that enough to be "over full" ? I can certainly drain a bit out if you think it might help.
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #6 ·
Ok so new problems, yay.....

I filled her up with the fresh gas, etc, and ran her for a while, was still blowing smoke but running OK.

I let it sit the last 3 days and went to start it up today and I could not get it started. It kicked over a few times and ran for about 3 seconds and would die, other times it would just crank and crank and I would get some blue smoke out of the exhaust as it was cranking. Other times it would load up while cranking and it would backfire really bad and then continue to crank and not start. I tried all combinations of choke/no choke/ with and without a bit of throttle, nothing would get it to start and run.

I believe the plugs need to be changed. But I am also thinking that the carbs might be out of whack. Is this a job a novice can complete or is it something that a shop should really do?

This sucks because I am only trying to sell the bike, and I don't have a way to transport it to a shop if it needs some work by a professional.

Kinda lost as for what to do now.....
 
1 - 6 of 6 Posts
Top