Topic: CB750K4 Bad Smelling Smoke

[Yoshimitsuu]

Hey all, let me preface this by saying that I did some work on the bike last year when I bought it but was not able to take it out for more than parking lot stints and down local roads. With that said, my bike always had a smell to it but it was never potent and it would mostly be when it started. Smoke was white which was likely the engine burning off moisture from storage.

However, this season I have taken it on a longer ride and noticed that it’s smoking more and it smells pretty bad unlike before. I haven’t done any work to the engine or anything and it’s pretty much been stored properly through the winter. I’m afraid it’s smoke that’s mixing with oil because it doesn’t smell like pure gasoline smoke (at least to me, my experience on old bikes is limited).

I suppose my questions are:

1) Could oil or bad smelling exhaust be caused by leaving my petcock open and oil mixing with fuel? I think I did this once by mistake and if this is the case I’ll change that oil ASAP.

2) If not, where would be the next place to look?

3) If it’s been stored since winter and ridden only minimally, is it too early to tell?

I understand that bikes that haven’t ridden a lot can smoke a lot but I just want to be sure as I love this bike and want to keep it for a long time. In addition, I’ve checked oil levels and I’m not losing oil at an alarming rate. I’ve plug chopped but I’ve assumed that my bike has run rich since I got it (prior owner installed PODs because they get the honeys) but I located a stock air box and K&N air filter to take care of that very soon. Any help is appreciated. Thanks!

[seanbarney41]

Also be awAre that this is not a 2014 civic, new and exciting smells are often involved and may be normal

[BobbyR]

Is it possible you have stored the bike with the gas in it. The small may be gasoline varnish.

[Yoshimitsuu]

Thanks guys! So far I actually changed the oil in the bike and also replaced the gasoline with new gas. I’m returning the bike to the stock air box so when I pull the carbs I will look through them and clean any varnish that could very well be in there I checked for dead animals, nothing in there.

I do have one more question however. My biggest worry is that the smoke is blue and that something is wrong with my engine. I checked the ad from the guy that I bought it from and one of the things listed as being tended to was the the pistons and rings were cleaned and honed (but then again, we all know how those ads work...) To me the exhaust smells bad but I’ve never actually seen it look that blue it’s more of a cloudy white when I actually do see it which I assume is it burning off moisture from storage (it’s running a bit rich, which I hope to fix as well with the stock air box). If there is something wrong with my valve guides and/or rings how would I know for sure? I’ve also heard that rings can take a while to seat and that after a job like that it could smoke for some miles. Again, it’s hard to tell but I just don’t want to do any damage to the bike. Thanks again for all of your help!

[Yoshimitsuu]

I figured I would post a video that would help. It’s hard to describe these things in words. Smoke is most noticeable when throttle is pinned and on startup. I smell it on a ride but I don’t see it much.

[BobbyR]

Oil smoke does not usually dissipate that quickly. Old school trick is to put a piece of clean white paper behind the muffler. You will see the oil on the paper. If it gets wet with gas it will dry, oil will not.