White smoke out of exhaust port 1 and 2

[surfish95747]

hey all, I am in the middle of putting my 1980 cb750k back together. I bought this bike from a guy who couldn't get it to run. He said all it needed was a new starter motor. I stripped the frame down, cleaned the engine, rebuilt the carbs, put a new starter motor in it and now just two days ago I got everything back together. I filled the engine with Shell Rotella T 15-40 and hooked fuel lines up to the carbs and gas tank.

It fires up no issues, even better when it is warm. I know at some point the carbs need to be synced ( I am in the process of getting my hands on a carb sync right now), but I am hearing a very loud ticking in the right top end of the engine. Also, white smoke comes out of  exhaust ports 1 and 2 ( even with the headers on) and the left exhaust puffs white smoke which increases as the engine warms up and idles longer, which it idles right around 1000-1200 rpm. What could the white smoke be? Does the loud ticking or knocking noise mean the valves need to be adjusted? Or does it need a complete valve job? Thanks guys!

[shinyribs]

Could just be out of adjustment. Unless it has oodles of miles, or was stored for a very long time (think rusty valves), it probably doesn't need a full valve job. But only a leakdown test can tell you this.

Out of synch carbs , even slightly, can make the engine produce all kinds of funny noises. So I wouldn't sweat that too much until after you get your carbs sorted.

White "smoke" out of a tail pipe normally is actually steam. But, since we're talking air cooled, we know that's not it. Unless you have a lot of water in your fuel. But that is unlikely since the bike starts well.

If it's real rich it could be puffing raw fuel out, which may appear white, but it's actually/typically grayish.

The same with oil. If it's puffing oil it may appear white, too. Though oil should produce a more gray/blue smoke.


Any smell or residue with your white smoke? You can check those two spark plugs for oil residue.

Any chance you done a compression test?


BTW, that's a real pretty color! What is it? And it's nice to see a twin cam with wire wheels, too!

[surfish95747]

Shiny, thanks! it was just a rattle can. Rustoleum Lobster Red. I'm a painting amatur and recovering from surgery so it was a good learning experience and a way to not go insane while in recovery.

Tomorrow I will get back to you as I will do a compression test and let you know. I did do a compression test when the engine was out of the frame, I was manually turning over the engine so the PSI's were significantly lower at 35 psi, but each cylinder had the same compression.

I rebuilt the carbs to factory specs and settings, so I imagine it is running a bit rich. When I give it throttle it takes a second for the RPM's to decrease after I release the throttle. I think that means its too rich?

The smoke just smells like exhaust, so I don't know if that means anything or not.

I've got to take the carbs off before I do anything else because I think I need to fix the float or bowl in carb #3 as gas just leaks out when the petcock is on and the carb drain screw is closed.

So, I will probably fix carb #3, put them back on and then sync the carbs. Then worry about any excess noises from the valves. Should I check my cam chain tension as well? How often should those be maintained.

[TOOLS1]

Too rich will not cause the engine to be slow to return to idle. These engines are "air throttled," so that means you either have a vacuum leak, or your throttle is hanging up somewhere. As for adjusting the timing chain, never hurts to do it, but will hurt if you do not.
TOOLS

[birdmannn101]

My CB750 smoked real bad and would only run with the choke on.  With some help here, I found out it was the idle jets that really needed cleaning.  There was a lot of popping and cracking too heard while it was trying to run.  After I cleaned the idle jets it ran great.

[shinyribs]

TOOLS1 wrote

 As for adjusting the timing chain, never hurts to do it, but will hurt if you do not.
TOOLS

Well said!

Slow return to idle is typically a vacuum leak. With these Cv's I've seen plugged idle circuits cause it,too. Underneath your pilot jet there is another brass tube that needs to be removed and clean,too. The emulsifier tube.

Two more things that are very easy to overlook on these carbs: First, the o-rings that seal the idle mixtures screws. If you got that,cool. If not, I can explain more in detail if you like. Should be o-ring-washer-spring in there. If not=vacuum leak. Also, on #2 carb bowl there is an extra o-ring that the other 3 don't have. Seals the port for the accel. pump passage.

Oh, and pull in your clutch lever when listening to rattles. They have noisy clutches and pulling in the lever will quieten it. That may be one noise you are hearing. If so, don't worry about it. They aren't 'supposed'' to do it, but they do. There are fixes for it, if the noise really bothers you, but it's not really hurting anything. Personally, I like it. :)

Lobster red..I' gotta find me some of that. Best wishes on your recovery!