Topic: What's that sound?

[bigjoshc]

So, I bought a 1973 CB350F at an auction.  After reading through this forum for a few weeks I finally got it running.  THANK YOU ALL FOR SHARING YOUR KNOWLEDGE!

Anyway, I took it down the road for the first time today.i only went 5-7 miles.  When I got back I noticed a strange whining sound when the RPMs are coming down after a revving.  I took a quick video (see below).

Also, I noticed some smoke or possibly some vapor/steam coming from the breather tube that goes up to the head. Something was dripping from the tube. The liquid that was dripping wasn't oily. Is it steam coming out of the breather?  Should I be concerned?

Since I bought the bike I've done the following:
-cleaned and rebuilt the carbs using an aftermarket rebuild kit
-oil change with new filter
-new air filter
-new points and condensers, and timed
-adjusted tappets
-adjusted cam chain
-synced carbs

Here's the video: http://youtu.be/baigA123Thk

[goldarrow]

Just run it.  Put 100 miles on it and see if smoke still there. 

[Trevor from Warragul]

Motor sounds fine.  Smoke from the breather is usually blow-by from worn rings/pistons.

[krusty]

My CB350F does that. Fumey oily smell too. Have a Cruzin' Image piston kit ready to put in when I get 'round to it.

[lucky]

If it was me I would be checking the top end to see if it is getting oil!!

Does not sound good.

[bigjoshc]

What's the best way to check and see if the top end is getting oil?

[Johnie]

Open the round caps on the valve cover and look in there with the motor running. You should see oil splashing around.

[hoodellyhoo]

My experience has been that most small cameras make engine noises sound worse than they are so it's hard to diagnose potential problems based on a video like yours.

That said, are you sure you cam chain is properly tensioned and that the mechanism is moving freely? The tensioner utilizes a spring that get weaker over time and can no longer provide enough force to tension the chain. If you run the engine long enough with a loose cam chain it will rub on the tensioner hinge, making noise and causing it to seize. There is a better method that what's in the manual for adjusting the cam chain on these motors. If you think this my be the case, do a search for 350 or 400 cam chain adjustment to help you get it properly tensioned.

[bigjoshc]

I pulled the tappet plugs and looked for oil.  It seemed plenty wet in there and I saw some oil moving around.  I had already adjusted the cam chain tension but I did it again just to be sure.  It's not cam chain noise for sure.  Maybe I'm just being paranoid.  The bike seems to run OK.  I've put about 50 miles on it since and have not noticed any problems other than the weird noise.

[jamesbekman]

You can do a compression check on the cylinders.

But like the previous post said, run her, rings expand again when heated up and run through for a while... 

[martin99]

As said, not easy to capture sound in this way. But for me it sounds almost like a spring binding as it coils out, got me wondering if the carb slides are binding on the way down? If you open and let go the throttle when the motor's not running (with the petcock closed so you don't flood it) does it make the same noise?