Honda Twins banner
1 - 18 of 18 Posts

·
Registered
Joined
·
41 Posts
Discussion Starter · #1 ·
Ok, so here is the issue....
My 78 CB400 T2 smokes (oil smoke) when it has been run at 55 MPH for 20+ miles.... if I run it for 5 or 10, no smoke.... When it does smoke, I can let it sit for 20 min, and it will be fine for a while... BUT.... tonight, it started to smoke, and I sat at the gas station for about 20 min.... got back on, rode 20 more miles, and NO SMOKE!... some times it would smoke after this... some times it dosent... What is wrong?
 

·
Sensei
Joined
·
27,183 Posts
Check oil level, and for fuel thinned oil...... Check compression......
 

·
Premium Member
Joined
·
670 Posts
Do you mean smoke from the pipes or smoke from the breather?
 

·
Registered
Joined
·
41 Posts
Discussion Starter · #4 ·
It smokes from the pipes, like the rings are bad.... but if they were, it would smoke all the time. The oil level is good now, but it gets low afer a while. What weight oil should I be using? Top end would involve the valves/guides?
 

·
Sensei
Joined
·
27,183 Posts
Fuel thinned oil gets past the rings and burns....Not to mention the damage the lack of proper lubrication allows....... Smell the oil on the dipstick, and remember to shut off the petcock when parking....
 

·
Sensei
Joined
·
27,183 Posts
Sorry, apparently I wasn't clear...Smell it for a "gasoline" smell.......
 

·
Premium Member
Joined
·
185 Posts
Check that the engine breather pipe is not blocked, also does it feed into the air box?
Could be that oil mist from that is being fed back into the carbs.
 

·
Registered
Joined
·
41 Posts
Discussion Starter · #9 ·
I cant see any oil in the air baox, and it doesnt look like its blockd... but, it does smell strongly of gas
 

·
Sensei
Joined
·
27,183 Posts
What smells strongly of gas?...The oil or the airbox?.....IF it's the oil, don't run the engine anymore until you change the oil and find out how fuel got in there.....
 

·
Premium Member
Joined
·
185 Posts
If the engine has been popping back through the carbs then it will smell of gas.
The reason I asked about the breather was if it intermitently blocks then the engine would build up pressure internally and could then force oil down the valve guides.
Just an idea.
 

·
Registered
Joined
·
41 Posts
Discussion Starter · #13 ·
and thats the black rubber tube going going into the valve cover?
 

·
Premium Member
Joined
·
185 Posts
Thats the one.
 

·
Registered
Joined
·
41 Posts
Discussion Starter · #15 ·
no, its not blocked.... but i checked compression and the right one is 140 PSI, and the other is 135 PSI. claymer says 185 +or- 14... would this be it, or is it probably the valve guide seals?
 

·
Sensei
Joined
·
27,183 Posts
Both readings are well below minimum specs...You need at least a re-ring/top end freshening job.....Once the head is off, you can check it with acetone to see if valves are sealing correctly........
 

·
Sensei
Joined
·
27,183 Posts
For the intake sides, fill above (before) the closed valve and look for any seepage into the inside of the head.... ANY leakage at all is unacceptable.......exhaust is "after" the valve (pour where the stem and springs are after setting the head so it "holds" the liquid.......)
 
1 - 18 of 18 Posts
Top