Smoking airbox? 1980 750 LTD 4 cylinder

80 deg and sunny today. I just finished up mile 17 of 40 on my way home from work. I pulled to the stop sign, saw there were a few cars coming, so I had to wait. I looked down and noticed my bike was smoking a little bit from the carb area. I figured I had a little gas leak or something. I look down, and believe it or not, my airbox was venting a little bit of smoke from the emissions system hooks to it. The hose must have popped off. I thought this was weird, and that the fumes she be getting sucked back into the intake. When I opened the throttle, it stopped. So, is this normal to be getting a little smoke from the crankcase breather. I was averaging about 60 mph for those 17 miles.

Your reed valves are probly toast and allowing exhaust to blow back thru the emissions system. You need to remedy this ASAP, as this will affect power and mileage.

Rip it all out and plug the airbox hole, and run a hose across the valve cover outlets. You dont need to remove the reed valves as this will render them useless.

GL.

So, you don't think that the fumes would be coming from the crankcase? I remember times when I would take the oil cap off my car and other bikes that were hot some fumes would come out.

I'm 100% ok with scraping the emission system. I just left it there because it wasn't causing issues. I would like to get some plates to just blank it off. Wasn't there a guy here that was doing it for people at a reasonable price?

Running the motor with the big hoses at the reed assy off, there should be no pressure/ ex gasses, only a small vacuum.
This will show if the reeds are leaking, as they are a 1 way valve, air gets sucked into the hole past the reed into the exhaust. Thee should be a full test in your FSM.

actually...the smoke is coming from the airbox out of the hole that the FSM attaches to... so it would be coming from the crankcase breather....

Sounds like it could be an oil issue, either type, temperature, or moisture. A small amount of fumes would be normal, hows the inside of the filler cap, any signs of moisture?
Unlike your car, there is no PCV system to recirculate fresh air into the crankcase, only the breather for the built up pressure to escape.

Fresh oil, correct type, weight, and level (crankcase not over-filled)??

Would sniff-test oil to rule out fuel intrusion into crankcase (which can cause excessive smoke from from breather).

Compression test figures within specs?

Good Fortune!

I'm thinking bad ring seal too. Do a compression check.

Valvoline motorcycle oil, 10-40 w/1500 miles on it, compression was done 1500 miles ago (and after sitting since '87) and it was 135 accross the board (cold, WOT).

There is no fuel intrusion... I know this because I check the level daily because I did have this issue when I first got the bike and was working on restoring it. Floats were misbehaving and let gas get into the oil. I never ran it though because I caught it beforehand...plus the bike wasn't running yet .

Correct oil level.

When you say check the oil cap for moisture, are you referring to a presence of a waxy, gooey substance?
I had an issue on my 550 w/ moisture on my sightglass window and was told that short rides are easy way to build moisture up. This bike doesn't have any moisture on the window and the rides are 40 miles every time (my work commute), so it is up to operating temp for some time.

I may have given you guys the impression that it is SMOKING. I just noticed a little bit of fumes, and these fumes did not hang in the air like they do when coming from an engine that's using oil. From what I can tell the bike hasn't been using any. The plugs look brand new and are finally showing some signs of that tan color after I richened up the pilot circuits, plus the pipes don't emit any smoke at all.

Maybe I should think about an oil change? It has been sitting since 87 and maybe there is just a lot of old crap that collected over the years that now needs to get drained out with the oil?

Yes the gooey looking white stuff would be moisture. Patton had a good thought about the fuel, didn't you have some flooding/ fuel level problems? If that was the first oil change from sitting all those years, then a fresh change would be a good Idea. Isn't 1500mi the recommended service?
Good to here it is running good these are great bikes, lots of fun.

I am not sure. I just had 3k in my head, but maybe it is 1500 mi. It's not the first oil change. When I first got it I put some real cheap regular motor oil in it just to get it running. I didn't even drive it at all with this oil in it. I drained that oil out and put the current oil in it.

Have you really pushed the bike yet?

Take her out and ride good and hard (1/4+ throttle/shifting 6-7k rpm) for about 15 minutes, then get on the freeway and let her rip for another 15.

Then roll back home and drop the oil immediately. Dont burn yourself

You'll be amazed at the crud that can come out of these things after sitting.

GL.