Smoke from under frame/footpegs and sketchy running

[TheEelBlaster]

Alright, I searched this forum and a few others last night for about 3 hours but could not find anyone else with the same problem as me. Here goes:

So, I bought my 72 CB750 four from someone last week for a fun bike to ride around and commuter. This is my first ever bike, but I do have a lot of experience working on my 74 VW Beetle that I figured I was a step ahead of some other people that have never done any work on an engine.

The guy I bought it from said he just changed oil, cleaned and tuned carbs, and it is ready to ride, it just needs a clutch cable. so I got a clutch cable, installed it, and it starts up after just a couple of cranks or one kick, it idles pretty well (I think?) it runs and it drives, but there is a very apparent problem.

Just under the frame, somewhere between the rear brake pedal, the footpegs and where the rear wheel is closest to the front wheel, there is smoke, quite a bit of smoke, it feels/looks like exhaust, but it very well could be smoke. I don't want to ride it if I'm about to explode the engine, but it also hasn't been on the road since 2005, so I feel like it just needs a good working in.

Unfortunately I have to get this in working order to be able to bring it to Cali to college with me where I will NOT have a shop to do any big stuff :(

Any suggestions of what to look at or check out?
Thank you all so much in advance!!

[TheEelBlaster]

Oh yeah, and the second part. I feel like there is some inconsistency with the gas getting from the tank to the tubes below the tank, and it just wont start up, like being out of gas, like possibly a clog. I dont want to break anything or remove anything that needs to be there, so I have not done much with that besides looked at it.

Practically everything is stock.

[TOOLS1]

Your smoking might be the crankcase breather on the back of the case. On the fuel, pull the fuel line, and see if gas flows.
TOOLS

[TheEelBlaster]

Just started it up again. ran fine. located the hose that was puffing steam like a train. rode it down my driveway and back up. Then let it sit and reved it some to listen to engine. there is a "clack clakck clack clack clack" noise while running (should I hear that?) and then some steam (or smoke?) started coming from the sparkplug nearest the sky when sitting on the side stand after running for probably 15 min. 5 minutes after that it "put put put died" and now when I try to start it up it seems like no gas gets to anything. Waiting then I will try again.

[TOOLS1]

I hope you did not leave it sit still, and run for 15 minutes.
TOOLS

[TheEelBlaster]

This is where I am a newbie. Some mornings I have to let my bug run for 15 minutes before it will even be able to drive. So I guess that was a poor choice? Did I cause permanent damage?

[RodneyCB750K1979]

Probably not since the motor didn't seize up.  Idling for extended periods of time will cook the oil seals and gaskets and could distort the aluminum parts. Was the steam or smoke from the spark plug with the spark plug still installed?

[TheEelBlaster]

The spark plug and wire was still installed, and the smoke/steam almost
immediately stopped when the engine died. I now know not to let it idle for
more than a minute or two? Does this effect the bike, for example, while
sitting in traffic?

EDIT.
Should I sea foam the oil tank and then do an oil change tomorrow? and see how it runs?

[motogrady]

You can let it sit and idle with a house fan blowing air across the fins of the motor.
The beetle has a small blower that moves air around that engine.
Sounds like you overheated it.  You were cooking the oil or grease that has acculmulated (sp?) around the plug base

I'd change the oil, charge the battery, and ride it around the block, close to home a few times.
Blow that crap out of it.
The fact that it idles for 15 minutes would tell me the carbs aren't that bad.

If it starves for fuel, look up the "son of sam" in the search here.

[TheEelBlaster]

Thanks, I did sea foam and changed oil.  should be doing pretty well now I hope. I tried looking up "Son of Sam" and nothing came up.

another thing is at my attention now, getting my bike road worthy, the throttle. it is extremely stiff and does not rotate back to idle by default. it just stays wherever I twist it, but it is very difficult to turn, I will kill myself if I can't fix it. is it a simple fix of a new pull throttle cable? or will I also need a new plastic throttle handle thingy?

[shultz_1978]

If it is like my 78 Just get both pull and push throttle cables, Clean out the tube throttle housing.

[shinyribs]

When Grado mentioned looking up Son of Sam what he meant was Spawn of Satan. Its the nickname given to the vacuum operated petcock on those bikes. There should be plenty of info detailing how to work around the SOS and regaining your fuel flow.

[shultz_1978]

What all years had the Spawn of Satan?

[LukeM]

I think they started in the late 70s.  I know my '79 had it.  I left it on mine, since it was a 750L.

It's a fuel management device, that allows gas flow while the engine is running, and shuts off fuel when it's not. It can be bypassed, as long as you're using the petcock on the gas tank.

As far as the smoke/frame issue, if you can make a video of it, that might help with diagnosis (unless it's not doing it as of 7/29/13).

Luke M

[TheEelBlaster]

Thanks, I will look up "SOS" when I have some more time to work on my new hobby. but for now, throttle cables are shipping, I woke up this morning with a puddle of gas under my bike (I guess something is working when the gas thingy is pointed up), and I need at least a new front tire.

Suggestions for tires?
I currently have an almost flat front tire, but the rear tire looks awfully new. I saw specs on tires should be 110/90/18 for rear, and 100/90/19 for front?
Rear tire says Kenda Challenger (this one --> http://www.motorcycle-superstore.com/3/31/401/6097/ITEM/Kenda-K657-Challenger-Rear-Tire.aspx) but reviews aren't so great for the front tire. Should I buy all new tires if the rear tire is not a good one to have? Also, what are some suggestions for tires? And what website should I but them from (are they possible to put on by myself), or should I go to my local Honda bike dealership that says they can get me new tires and install everything for me for under $200?

Thanks a ton for all the input so far folks!