Topic: Burning Oil

[NewOldSchool]

So I have had my '74 CB750 for a little over a week now and it's running great. Ive changed the oil and filter, put in fresh plugs, adjusted the cam chain and valves, adjusted the points  and had the bike timed and the carbs balanced. There are two small things bothering me though. After riding around for a while and the bike has warmed up completely I notice a small amount of smoke seeping out of the end of the breather hose that dumps out around the swing arm pivot. This only happens at idle or after giving it a quick rev. Also the bike still rattles quite a bit when in neutral, not anything like it did before the tuneup, but it still does. I know its a 36 year old bike so I don't expect it to idle like a new sport bike.

[gnarlycharlie4u]

So I have had my '74 CB750 for a little over a week now and it's running great. Ive changed the oil and filter, put in fresh plugs, adjusted the cam chain and valves, adjusted the points  and had the bike timed and the carbs balanced. There are two small things bothering me though. After riding around for a while and the bike has warmed up completely I notice a small amount of smoke seeping out of the end of the breather hose that dumps out around the swing arm pivot. This only happens at idle or after giving it a quick rev. Also the bike still rattles quite a bit when in neutral, not anything like it did before the tuneup, but it still does. I know its a 36 year old bike so I don't expect it to idle like a new sport bike.

what's your oil level like?
Also, are you completely sure that your piston rings are in good shape or that there are no damaged pistons/cyl?

[KingCustomCycles.com]

A compression test would settle any disputes on cylinder condition.  It is normal for these bikes to puff some vapor out of the crankcase or tank vent as they burn off accumulated condensation in the oil.  The rattle may well be normal also as it is hard to determine without a video or audio clip. 

[gnarlycharlie4u]

A compression test would settle any disputes on cylinder condition.  It is normal for these bikes to puff some vapor out of the crankcase or tank vent as they burn off accumulated condensation in the oil.  The rattle may well be normal also as it is hard to determine without a video or audio clip. 

exactly.
OP, just how bad are you burning oil? Do you have blue smoke in the exhaust or is it just oily vapor through breather?

[NewOldSchool]

As I've said I just changed the oil its right at the "full" mark on the dip stick. No blue smoke out of the exhaust, not even on start up or when cold. Just the little bit coming out of the breather and a tiny bit if I open the oil cap after a ride.

Ill take video of the bike running soon as I can.

[gnarlycharlie4u]

As I've said I just changed the oil its right at the "full" mark on the dip stick. No blue smoke out of the exhaust, not even on start up or when cold. Just the little bit coming out of the breather and a tiny bit if I open the oil cap after a ride.

Ill take video of the bike running soon as I can.

tbqh... it's probably not an issue.

[Spanner 1]

The complete cure for that would be to ride the bike for at least 100 miles in one day, when you get home you'll be amazed at the much better bike you have..... these old SOHC's hate short trips, stop/start stuff etc. Do a long ride and then see what problems that eliminates, you'll be amazed at the fab bike you didn't know you had.
( Caveat )..... 3,000 mile service, just like it says in the book, done first .... still no other substitute for miles to produce a smooth running, easy starting bike.  

[Roach]

Italian tune up, works all the time.

[NewOldSchool]

The complete cure for that would be to ride the bike for at least 100 miles in one day, when you get home you'll be amazed at the much better bike you have..... these old SOHC's hate short trips, stop/start stuff etc. Do a long ride and then see what problems that eliminates, you'll be amazed at the fab bike you didn't know you had.
( Caveat )..... 3,000 mile service, just like it says in the book, done first .... still no other substitute for miles to produce a smooth running, easy starting bike.  

I absolutely agree. I completed the entire 3000 mile service last week, then went for a nice long ride and got the bike nice and hot. It does run so much better once its been warmed up and opened up a bit, when I get home it runs soooo smooth compared to the morning when its idling after the 1st start of the day.