Topic: Need Help: Looking at buying a '74 CB750 with 3100 original miles

[VTSlim]

This weekend I'll have the opportunity to purchase a 1974 CB750 from one of my best friend's inlaws. The bike was purchased new by the one and only owner back in 1975. Obviously, with only 3100 miles on the clock, it's been sitting idle for much of it's life. The bike has a 2007 Virginia state inspection sticker on it, but I'm told it has been ran a few times since then.

The bike is all original except for the Kerker 4-1 (grrrrr!) and paint has been described to me as being "beyond very good". If these pictures show up, you'll see that it's just dusty and a bit rough around the edges from sitting in a barn for most of it's life.

It's a no-brainer, right? Well, not exactly. Here's where I'd like to enlist the help of some of you guys who have been wrenching on these things for years. I'm told that it has a blown exhaust gasket, and carburetor problems, both on cylinder #1. Secondhand, I was told that the float pin in carb #1 was broken, so a new one was riveted on, which caused the exhaust gasket to blow. Sounds a bit fishy to me. From the pictures, you can see the discoloration around the exhaust port. To me, this doesn't look like exhaust soot, it looks oily/gassy.

At a minumum, I plan on performing a compression check, analysing the "substance" around the exhaust port, and inspecting the different spark plugs for comparison. I'll also have to ask a few more questions regarding how exactly a carb float pin caused the exhaust gasket to blow. 

The other primary known problem is that the brake master cylinder is leaking. Oh, and the sissy bar has a broken bracket (dealbreaker!).

Since I'm sure that the asking price will be amongst the first questions, I'll go ahead and throw it out there that they're hoping to get $2000, which is down from the $4000 that they originally wanted a couple of months ago. I'm not inclined to pay more that $1500 for the bike, even if the exhaust gasket/carb problem turns out to not be a major problem.

I'd really appreciate any feedback regarding the potential problems with cylinder #1, and the asking price. I'll be sure to follow up with an update after I take a look at it on Saturday.

Thanks!

[Jerry Rxman Griffin aka MuthaF'er]

It sounds like it's a good deal for a 3100 mile bike. If you get it for $1500. However, blown exhaust gasket??!! The exhaust gasket is a round copper seal which sits between the exhaust and the head. That sounds like BS or ignorance. Head gasket leaks are expected eventually. And head gaskets don't blow, they usually leak/seep. The float POST pin was probably broken during rejetting for the Kerker when the pin was removed incorrectly. JimF may be able to microweld that for you. He has a laser welder and can do aluminum. Riveted on??!! WTF?!

The master cylinder probably just needs a kit which is available. New/NOS masters are not available but David Silver Spares sells a close replacement so that's a non-issue.

A good Kerker can get you a nice down payment on expensive replacement 4 into 4's. Will need to/should double check the carb work that was done. Make repair/replacement/jetting changes.

If it is in good/new appearance condition the mechanicals can easily be overcome.       

[VTSlim]

There is another thread with the same topic due to a network error I was having this morning, but I'm going to go ahead and reply to this because you addressed what is really the whole point of what I was asking.

To me, there is no way that the exhaust would choose to "blow out" a gasket which should've been crimped between the flange and the head when it could easily escape through an open exhaust pipe instead. That's why I was particularly curious about what the other causes of the mystery substance on the head fins could be, and why. Blown valves causing major leak-by? Blown head gasket? I've been trying to wrap my brain around why an exhaust gasket would blow in such a way ever since I first heard that...

[Jerry Rxman Griffin aka MuthaF'er]

Back to the other thread........ found it after the fact.