Topic: Burning Oil or Fuel Around Carb Boot/Bowl - '74 CB750

[matthew.hyndman]

I'll preface by saying I'm a novice of mechanics and bikes, so I apologize if there's an obvious conclusion here or another thread I should be referencing.

I've had my 1974 CB750K for a few years now and have only performed basic maintenance on it. As I was winterizing it, I noticed what looks like burnt fuel or oil around one of my carb boots and float bowls (see image attached). As I was running the fuel out of the carbs, that area was smoking mildly.

Any ideas on what the issue could be or what I should be doing about it?

Thanks in advance.

[setdog]

i wouldnt call that 'smoking mildly' considering there shouldn't be any smoke at all .  i wouldn't be running that bike as it looks like its about to catch on fire.  maybe im being over dramatic, but yikes.

i get those carbs off the bike and on the bench asap and start going thru them, and for safety i would dump all the fuel in the tank and plan on not riding or starting it up for a bit

i would immediately be looking to replace the carb boots at the least, and perform a thorough inspection of the carb bodies, to start...and then worry about a scheduled tune up procedure, involving ignition timing, valve adjust and cam chain

[seanbarney41]

in the video, you can plainly see the smoke coming from the cylinders in between 2 and 3 below the carbs.  They get hot.  Any foreign material there is gonna burn.

[ekpent]

 Do you have the breather hose hooked up at the nipple coming out the the middle/upper part of the valve cover there in the back and if not is oil running down there. Burning oil does have a distinct odor and flavor. Might be some other oil leak also.

[newday777]

Are your valves adjusted properly?
An intake valve too tight can be a cause to push exhaust gasses out the intake, the popping in video and smoke, leakage seen.

[matthew.hyndman]

@newday777 I'm not sure, I haven't adjusted the valves since I've owned it. The popping in the video might just be the gas I'm running out but noted anyways that I should adjust the valves. That's this procedure? http://www.sohc4.net/cb550-faq/indexphp/tappet-adjustment-procedure

@ekpent I'm not sure I'm following. Are you referencing a breather hose in the area shown in the photo or somewhere else?

@setdog It ran well all season up until this point, so it just snuck up on me. This was back in November when it went away from the winter and it hasn't been run since. I've never removed boots, carbs, etc. so if there are any good starter materials or threads I'll take anything I can get my hands on.

[andy750]

I think Ekpent might be correct - the breather hose is the black hose in your photo at the back of the cylinder head - may be leaking from there if you overfilled with oil. Here is what I would do:
1. Clean area around the back of the engine in case anything has leaked.
2. Check the oil breather hose is on tight
3. Check the oil level (when bike is warm)
4. Refill gas tank/carbs with gas and run the bike for a mile and then check for any leaks.

My guess is something is leaking onto the rear of the engine and causing the smoke. Probably not the carbs - as even if they were overflowing they would not smoke like this - and I have had overflowing carbs That smoke looks oil-based.

Nice K4 BTW I have one myself - since 2001.They are great bikes. Id take the previous suggestions though and learn how to work on the bike - valve adjustments, cam chain adjustment - its not hard - get a manual (Shop Manual or Haynes manual or Hondamans book) and some basic tools (10 mm, 12 mm, 14 mm, 17 mm wrench) and a JIS screwdriver (much better than a #2 Phillips).

Ask questions if unsure - this is what the Forum is here for!

good luck!
Andy

[ekpent]

@newday777 I'm not sure, I haven't adjusted the valves since I've owned it. The popping in the video might just be the gas I'm running out but noted anyways that I should adjust the valves. That's this procedure? http://www.sohc4.net/cb550-faq/indexphp/tappet-adjustment-procedure

@ekpent I'm not sure I'm following. Are you referencing a breather hose in the area shown in the photo or somewhere else?

@setdog It ran well all season up until this point, so it just snuck up on me. This was back in November when it went away from the winter and it hasn't been run since. I've never removed boots, carbs, etc. so if there are any good starter materials or threads I'll take anything I can get my hands on.

I looked closer at you pics and did notice your rubber breather hose is attached but do see some oil residue up around that area. Make sure one of your tappet covers is not leaking or any other places around that area.

[matthew.hyndman]

@andy750 Very helpful, thanks. I'll start there. I've done a few things on it so far (oil changes, cam chain, drive chain, etc.) but I'm pretty much doing everything for the first time so anything around the valves is new to me. Glad the K4 has treated you well, I love it so far.

@ekpent Thanks, that makes sense. I'll check that breather hose and the tappet covers.

[setdog]

There does seem to be quite a bit of oil on those rear fins, which I would think is unusual.  oil burning off the fins would def create slot of smoke.  In the photo, looking at residue around the tappet cover (cylinder 2), could you simply have oil seeping out under the tappet cover?  Or too high oil level as suggested earlier.  Check the condition of the tappet cover oring.  Residue around carb bodies could be built up oil particles getting flung around from air passing thru cylinders