Topic: 1977 CB750 Four K - How can I deal with Gas/Oil leak from Engine after Winter?

[jpham1802]

Hi everyone,

This is my first post on the forum, and I'm hoping to get some advice on how to tackle a gas/oil leak from the engine of my CB750. I apologize in advance if this question has been answered. If anyone can send me the links to such similar posts, it would be a great help! But if not, below are (1) the problem, (2) my questions, and (3) the bike background. 

Problem: Two months ago when the snow started to melt, I smelt gasoline near my bike on the driveway. After taking a closer look, I saw gasoline dripping down the engine fins; and 2 steps near the bike, there was a big oil stain on the ground (see attached picture). There was also what seems like oil leaking from the top end gasket (also see attached)

Questions:
1. What would be the proper orders to examine and pinpoint the problem? Or, what could have caused this leaking problem?
2. My guess is that the oil may have leaked through the gasket...If that the case, should I may as well just take the whole engine out and rebuild it? I am willing to do so cause this could be an awesome opportunity to learn. I am not planning to ride this summer either way.

The bike background:
It is a 1977 Honda CB750 Four K (I believe it is also called the K7? Please correct me if I am wrong). I bought it last summer. The previous owner had it since 2001 and rode it until 2009. It was stored in his garage since then. When I got there, the bike started and I was even able to ride it home.
However, I stopped riding it after 1 week when realizing that it had a problem with the rectifier as the battery didn't take the charge (but let's leave this for another day). So, the bike sat on the driveway all summer. When I tried to push it inside my garage before the winter hit, I found myself couldn't, due to the seized drum brake.

My biggest regret was that I kept procrastinating dealing with the brake issue, that I ended up leaving the bike outside throughout the whole winter. Not until recently after I dealt with the rear wheel, that the bike is finally inside the garage. Learn the hard way.

Thank you so much for all your help! Please let me know if there is any other information I could provide. And I also apologize for my grammar. English is not my mother tongue.    

[golfman]

Looks like you have a couple problems the oil leak would be a head gasket which is a bigger job it would not have happened over the winter . The fuel sounds to me like fuel line , gas tanks , or petcock maybe even a stuck float .

[disco]

I would deal with the leaking gas problem first. More than likely 1 or more of the float valves is passing gas.

The oil leak doesn’t look bad enough to worry about. I would wash it down thoroughly and monitor it for a while. Seen too many people “keen to learn” who pull these apart and never complete it.

[BenelliSEI]

+1 to Disco’s comment. Get it running. Ignore the oil leak, looks minor.

Fuel will be leaking from the petcock, or a stuck float (if you are lucky). Fill it up, open the petcock and if an overflow hose is leaking from a floatbowl, tap on it (the fliatbowl) with the end of a ratchet wrench. Sometimes that will free off a sticky float/ valve.

If your unlucky (my actual problem today) you will spot the fuel cross over tubes (from carb to carb) leaking. The only way to replace them is take carb one and four off the rack, after you take the carbs off the bike........

[ekpent]

 If you had your petcock on the fuel tank turned off while it was sitting and it still leaked fuel out of the carbs then the petcock is a leaker which needs fixing first. Might want to check/change the oil for gas as some or a lot could have got in the crankcase. Carb cleaning may be in its future also if those leak badly with the fue tap on.

[jpham1802]

Thanks everyone for your comments! I followed your advice and inspect the petcock and fuel lines and they all seem fine. So I narrowed down the problem must be in the float valves.

I have taken off the carb. A few notice, there seem to be fuel stains on carb 1 and 4 (see pictures). And when I removed the carbs there was still some fuel left in the carb 2 dripped out.

[HondaMan]

I can't open your pictures, but have these observations for you:
1. If the head and engine was leaking gas, the cylinder(s) filled with gas.
2. If #1 is true, then you MUST change the oil, draining the crankcase, and change the oil filter. Once it is running again, change it again in about 50 miles.
Gas is a strong solvent, and will wash all lube from the insides of the engine. And, it makes nasty fumes that cause more troubles.

Overall: check the fuel petcock on the tank. If it does not shut off the fuel in the OFF position (where it should be set by you every time the engine is shut off for more than a few minutes) then it must be repaired so it works, or this will happen again!