82 CB750C smoking and missing a little. Need help plz.

[GreenSkullCB750C]

Hello all 👋🏻 CB noob here new to the sight and the CB life. Just purchased my very first 1982 CB750C. I have had the bike for about 2 weeks now and been going over things and it’s has been running great at least I thought, untill a mis fire showed its ugly self. Pulled the plugs and this is what I found. Not sure about firing order, think its from left to right 1 2 3 4 right? So if that’s true, #1 and #4 showed black soot like material covering tips and electrode of spark plugs. #2 and #3 showed light tan color which if I studied correctly 2 and 3 are fine but 1 and 4 are rich or my heat range for the plugs are not correct! Is that right? clean the plugs and reinserted in the block. The guy that sold it to me told me that he had the carbs cleaned and reassembled with a sync. Not sure on that either 🤷🏻‍♂️ Checked the gap on all 4 and set gaps to .026, my book says 0.24-0.28, is this correct? So many questions 🤦‍♂️ Still not entirely sure 🤷🏻‍♂️ Then I noticed that the #4 header pipe was smoking at the block and out the pipe (straight pipe btw) when bike ran for to long! Is this a form of over heating? Could there be a bad valve guide letting oil in #4? Any and all knowledge would be greatly appreciated!!! Hopefully TOOLS can shine some light 🙃

[TOOLS1]

Since it is 1 and 4 and they are on the same coil I would start looking at the ignition system. First, check to make sure that the charging system is working. If the charging system on the DOHC bikes is not working it will cause ignition problems. Then I would check the spark plugs, wires, and coil. There are instructions on how to do all this in the Honda Factory Service manual which can be downloaded from our manuals thread here on the home page. Or you swap the parts one at a time with the ones for the 2-3. If the problem mover to the 2-3 side, you have found the problem.
TOOLS

[GreenSkullCB750C]

Thanks for some direction TOOLS. I will take a gander at all the electrical and see what I come up with! Any idea as to whats making my #4 header from the block smoke after after getting hot? I’m kinda thinking a valve seal has gone bad allowing oil into the chamber  or is this a byproduct of ignition misfiring? Ima noob and want to be sure about it before I go and install new oil seals and stuff 😬 Again  Thanks for shining some light on it!!!

[TOOLS1]

What color is the smoke? Where exactly is the smoke coming from? Is the rubber plug that goes over the cam chain tensioner bolt missing? Is the valve cover gasket leaking?
TOOLS

[GreenSkullCB750C]

It doesn’t start smoking untill its hot! As I let it idle, smoke starts to seep out at the header flange where it connects to the head! It all happened a day ago while I was riding. Didn’t do none of this before. Something happened. Scared to ride it so haven’t since a day ago. I shut it off and let it cool! Still smokes as it cools. Grey in color not sure about blue tint couldn’t really see being that its just seeping and not being thick in nature! Faint for most part. Also coming out the end of #4  like going through pipe and out but thats expected. Its also coming out of number #1 but not from the header flange and not as bad as #4 thinking thats due to misfire! But 4 is noticable!!!  Could a coil that drives 1 and 4 that’s bad cause 1 and 4 spark plug to get fouled which looks like black soot??? Tricking me into thinking air/fuel ratio is off but really its just not igniting??? And no valve cover is not leaking from what I can see! And no the cam chain adjuster are still intact. Haven’t touched em! Also it became a little harder to stay running, wants to shut off a couple times after choking. Thoughts 🧐

[GreenSkullCB750C]

Ok so I pulled the #4 pipe off so I could see the valves, they didnt look wet! Possibly rule out the oil leakin through valve stem seal. I started the bike with the pipe off and let it idle, every so often a puff of grey smoke pops out, as it was getting hotter, the smoke became more and more as it got hotter, so shut it off and reinstalled the the header back on and tightened it! Apparently the exhaust pipe to the head wasn’t tight enough making it seep out. That’s correct now, no seeping from pipe now. Definitely missing when I put load on it, blipping randomly as I try to increase speed. I believe that the charging system is in function order! Gonna go and grab 2 new coils, 2 inner and 2 outer plug wires and 4 new saprk plugs! My question now is what type of plug is best for being the correct heat range? Pulled the plugs after cleaning once and 1 and 4 plugs  keep getting black soot on them! Is this a sign of the misfiring or incorrect spark plug heat range? Thanks again for the help!

[TOOLS1]

You should not require a different heat range spark plug from one cylinder to the other. If you downloaded the factory service manual it will tell you the correct plugs to use. It sounds like 1-4 are not running correctly. Could be ignition not working correctly, or vacuum leaks on those two carbs.
TOOLS

[GreenSkullCB750C]

Thanks TOOLS for your guidance good Sir.  
Also here is what she looks like at the moment.

[TOOLS1]

Nice looking bike. That airbox does not look bad on it.
TOOLS

[GreenSkullCB750C]

Thanks
I think it maybe its a chrome trim peice but yea it it all looks pretty good for being almost 36 years old! I’m gonna be looking for the coils, wires and plugs! Any trusted online website suggestions for the parts? Thanks again!

[TOOLS1]

Any auto parts store can get you the correct NGK spark plugs and wires. Coils and plug caps, try vintagecb750.com or Z1enterprises.com
TOOLS

[GreenSkullCB750C]

Thank you sir. Will update later!

[GreenSkullCB750C]

Hey guys back with that update I promised. So this has been a journey for me but I learned a great deal about the bike and what essentially was happening. Starting off I want to first and foremost exaggerate the fact that these things called "SPECS" actually mean something when it comes to certain models. Okay with that out of the way let's begin. I had a nasty little "DUO" of problems going on. First thing was not the Ignition Coils like I first presumed. No, It just so happen be this little thing called the "Air Cut-off Valve". Basically this operates with a rubber diaphragm located on the left side of each carburetor. When the throttle is open i.e. demanding more air the diaphragm due to the vortex of pressure change, closes so when cruising or gettin on it, it's closed allowing more fuel trim from the jets. Now when you close the throttle i.e. slowing down, the closing of the throttle butterfly changes pressure therefore opening certain fuel passages that allow the cylinder to keep getting fuel while the butterfly is closed. This "Air Cut-off Valve" being bad was making the cylinder basically run dry through the cycle of combustion. Now on to the Second part of this fiasco. The second problem I encountered was I absolutely had the wrong type of Spark Plugs!!! This was the icing that topped the cake and let me explain why.  At first glance when the problems all started, I went off what kind of plugs the previous owner had had in the motor. Total mistake on my part! the plugs he had were platinum or iridium center electrodes. When I bought new ones the first time they were still wrong smh.  Finally I discovered that there are Canadian models of CB that require a specific plug I guess for a certain reasons I'm unaware of BUT, My model calls for a copper center electrode spark plug. So with the number 4 carburetors "Air Cut-off Vlave" blown the cylinder wasn't getting any fuel but the other 3 were! Then the spark due to the wrong material the spark plug had, caused weak firing of the spark and it was erratic not consistent which in turn was also creating a misfire. So 1 misfire caused by 2 seperate problems! Now she purrs like a kitten but growls like a tiger! Hope this helps! Cheers  

[TOOLS1]

Awesome! Glad you got it sorted out. Thanks for the update.
TOOLS