Engine noise/knock??

[PharmD750]

So I recently bought a 78 CB750K and changed the oil and filled it up with 93oct gas since it hadn't been run in quite a while. I have zero experience with older bikes, but to me the engine does not sound totally right. I don't know if there is some sort of knocking going on in the motor or if that is just how these older motors sound. I tried getting the valve covers off this afternoon without too much luck. Most of the valve cover bolts came off easy but 3 are being really stubborn and I did not want to risk stripping them since I don't have access to a lot of specialty tools. I am going to try and post a video of the motor running shortly once I get everything back together. I am also going to see if I can see anything through the valve cover inspection holes. I rode the bike around the other day (about 4 miles) and it doesn't seem to lack any power and the noise doesn't get louder as I give more throttle. Sometimes when I give it a lot of throttle the motor chokes out, not sure what that could be either. Hopefully someones got some ideas for me. Thanks in advance!

 

[PharmD750]

Ok so I had to put it on youtube... not really sure if you can hear what I am trying to get you to hear but its worth a shot. The first time it dies is when I tried to rev the motor...

Also I took the gas tank off before this and noticed this bolt sitting inside a hose that comes from the carb. Can anyone tell me why this might have been there or what that hose is for? Looks like a breather of some sort. Thanks for your input!

 

[PharmD750]

I also drove it and it has, from what I can tell, all of its power. It is definitely faster than what I expected it to be when I bought it last Sunday.

 

[dirtdigger]

It is hard to tell exactly but it sounds like either a loose valve or an exhaust leak at the head. Engine needs to be removed before valve cover etc can be removed from the motor so no reason to remove the bolts. Valve adjustment is done through the inspection covers.

 

[PharmD750]

I was thinking it was maybe a loose valve. I think its on the left side of the motor that's why I had my phone on that side. Thanks for taking a look.