Topic: Cb750 tank/seat question (year specific)

[KrautKoffin]

First time poster, lurked for a bit.  so I've been eyeing a 77 cb750 on Craigslist but the tank and seat are in bad shape. The tank has the worst knee dents I've ever seen and the seat is tore up. Can I find a minty tanks for an earlier year (sans the door) and install it with a new seat? I know the tank sizes changed and from what I could read, the only issue was the stock seat not mounting correctly. I'll be making my own cafe flat seat for this bike. Any help is appreciated!

[Wobbly]

The F tanks will definitely fit, and they also work with a café racer handlebar while the original K7/K8 tank does not work with any café bars I have seen (too wide and thus too close to bar ends, switches).  The Cuppini bar works on European models that have the steering lock on the side. Everything else, you either dent your tank, break your fingers, or cannot lock. Not even Laverda's Brevettato with multiple adjustment possibilities works unless you install it upside down. There is a new K7 tank available at CMS for $ 1600. It's the last one they have. The last new ones in alpha candy red are probably the two in my basement  . I also have one in near mint condition and a black F2 tank  N.O.S. with slight shelf wear (rubs), but they won't go cheap. For a café racer setup, you have other tank options, and it doesn't make sense to put a new or mint tank on if you repaint. But, I still recommend the F tank for best clearance.  The F seat and earlier K seats fit--but with modifications. The K7/K8 hinges and lock are located in the same spot as the earlier model--but on the opposite side of the frame. I also have a couple of K7 seats, modified and unmodified, with new upholstery for sale. The Italian company GAMAN made sports seat especially for the K8, but they are very rare. I tried the F1/F2 sport seat on my K7, and it looks and fits good too. But, again, hinges are on the opposite side and the chrome bar around the seat has to be replaced with an F-type one.
I have seen earlier K tanks on k7 bikes. So, it must work. I just don't have any experience with them and don't know what modifications, if any, are in order.

[KrautKoffin]

Thanks for the reply! I only said new tank because I'm dreaming of finding an undented tank for cheap. Good to know someone out there hoards seats and tanks! There's a local bike swap meet here next weekend that I'm hoping to score a tank at. The F tanks were from 70-76, correct? I guess as long as the tanks mounts up I can always build the seat around it. The tank on the bike now is on bad shape, so anything will fit is an improvement 

[754]

F tanks are 75-78 the first two years are probably different than the last two.

[KrautKoffin]

Ok cool, so basically all cb750 tanks will fit my 77, but the F tanks are smaller than the K tanks?

[Wobbly]

I am not sure what is required to fit the K6 or earlier tanks. The F2,F3 tank fits perfectly, and I don't think it's fit is different from that of an F1 tank. The K7/K8 tank holds 19.5 Liter, the F tanks hold 17.5 total if I remember correctly. Café Racer bars work with the early K tanks, just not well with the K7 tank.
On a side note: the chrome chain guard from an F2 fits perfectly on a K7. And the chrome horn from the K6 also fits nicely--although you have to change the connectors. The K6 horn looks better and is easier to obtain. Aside from that, the K7 shares a number of things with the F1 (the front disc brake for instance, which is larger than on earlier models). Finally, the side covers of a K7/K8 will also fit the F model and vice versa.

[750K]

You can fit early model tanks on a K7, the deal is they are shorter in length so you'll have to figure out mounting a seat. The stock K7-K8 seats have hinges on the left and lock/release on the right, the pre 77k's are reversed. You'll likely want to look for a K tank from the mid years, the petcock is on the left side of the tank just like the stock K7-8 tank. The early K tanks have the petcock on the right, I'd expect fuel line routing to be easier if the petcock was on the left. The idle adjust screw on the 77-88 carbs is up top on the right side of the carbs and the fuel inlet is on the left between #1-2 carb bodies.

Ive got an early model tank with a right side petcock and it drops on no problems, I can't remember if the mounting rubber on the frame lines up with the tanks mounting tab. By the looks of it the tab is the same length on both tanks but the back end of the early tank is maby 2'' shorter than the stock K7 tank.

I can take good measurements of both if you need them, I have a spare k7 tank thats off my 77 at the moment as well as a 72 K tank sitting around.

[KrautKoffin]

Thank you both for the input, this is my first bike and any help is greatly appreciated! I would love some measurements if you can get them, as long as the F tanks mount up like the k tanks the seat won't be an issue. I'm going to make a flatback seat so I'll just extend it forward if need be. I'll definitely be looking for an F tank now with no dents and bad paint (I'd hate to paint a nicely painted tank) with the petcock on the left side!

[lucky]

The 77-78 tanks are about 1 inch longer in the back end.  Thats it.

Some tanks have the petcock on the right and some are on the left. Watch that.

[750K]

So with the early model 72K tank upside down it measures 20.5" from the tunnel at the front to the end if the rear tab, the 77k tank is 21.5" from tunnel to end of the tank not the tab. So 1" longer on the 77-78k tanks.

[RSchaefer]

F0 thru F4 ('75-'78) gas tanks are the same and interchangeable with the exception of the petcock.  The '75 - '76 petcock is different then the '77-'78, different threads.  Left petcock on all.

[Mr Freeze]

Does anyone had a 76-78 F tank available?