Topic: CB750K8 tank swap options?

[gearsoup]

I'll be starting work on my '78 CB750K later next month, thinking I'm going to go with a restomod look. If it was an older K bike, I'd likely bring it back to OEM look, but the '78 is just "meh" to me. One thing on my wish list is the fuel tank, as I do really like the look of an exposed fuel cap (as opposed to the door/cover that the 78 has).

I've read that the K6 and older tanks do fit, but a gap is left at the seat. I'd like to retain the stock seat (since I just received a new reproduction unit), but don't mind if I have to cut/relocate the hinge and lock assembly to make an older tank fit proper. Is this even possible, or should I just stick with the '78 and make the best of it? I know Carpy has a weld in bung and cap, but I'm unsure of it's compatibility to the '78 tank.

[BenelliSEI]

I’ve modified a ‘78 550K tank (almost identical to the cb750K) to take a 3.5” Monza style cap. We removed the door and welded the threaded spool directly to the tank below. Closed off the overflow hose from the opening under the “door” and removed the hinge plate and lock mechanism. Cut a large hole in the lid (to fit tightly over the spool), then welded it in place and then bondo and paint. It actually looks really nice.

[gearsoup]

Do you have before and after pics?

[Kaze]

What is most critical is where your K8 carburetor sits vs. the K6 tank's fuel tap.
My K7 frame (same as K8) has a K6 tank on it, BUT I have a K6 carburetor too.
The rubber hoses between my carbs and engine are 2" long. If your carbs sit closer to the engine, then the fuel tap will hit the carbs.
It's about 11 1/2 inches from the front of the K6 gas tank to the fuel tap.

SEAT ISSUE:
The K6 tank sits perfectly on the frame, and the rubber tank cushion in back slides onto the back of the tank as it should. However, there was indeed a large gap between the seat and tank. At least an inch if I recall correctly. Unless you love doing everything yourself, having the seat foam altered, and seat reupholstered professionally would be a good option. Especially if you have a quality upholsterer in your town.