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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: FTR on February 07, 2026, 06:34:57 AM

Title: Fit a post 85 fuel tank to an 84 bike
Post by: FTR on February 07, 2026, 06:34:57 AM

Hi brick gurus,

I've done a search on this but nothing really answers my question.

I have an 84RS bike with a tatty fuel tank. The existing one has the thermistor fuel sender unit and a centre mount for the rear of the tank to secure to the bike frame. Ive been offered a later tank that's in much better shape, no leaks and it has the float type sender unit. The sender unit has been removed from the tank but the guy has it and can dig it out.

Can anyone tell me how practical it is to swap the older tank for the newer? Im not worried about the fit to fairings etc as they are all going, it's the fit to the frame and connection to the electricals I'm concerned about. I have an after market seat which clears the mounting bracket on the back of the early tank.

- is it possible to refit the sender after it has been removed and get a reliable gas tight seal?
- Is there any conflict between the frame and the underside of the new tank?
- Is it possible to adapt the wiring connector on the older bike to the newer tank fuel pump etc?

Many thanks

Stu

Title: Re: Fit a post 85 fuel tank to an 84 bike
Post by: daveson on February 08, 2026, 03:35:52 AM

Dunno. This is one of those questions that could give me a bit of mental indigestion.

Sometimes, in a situation like this, I'd ask myself "do I really want to make a rod for my back, or should I just sell the modern tank and put the money towards a suitable tank? As a clue I'm pretty easily convinced if one of the options is an easy way out.

Title: Re: Fit a post 85 fuel tank to an 84 bike
Post by: FTR on February 08, 2026, 09:04:36 AM

Thanks, the more modern tank is pretty inexpensive so was tempting to try to swap it out. I’ve since located an older tank so it will be interesting to try the two side by side and I can answer my own question.

Title: Re: Fit a post 85 fuel tank to an 84 bike
Post by: frankenduck on February 19, 2026, 05:02:07 AM

It is possible but not practical IMO.

To start with you'd need:
1 - A newer fuel level sender (and newer cluster if you want the low fuel light to work)
2 - Rewiring to make 1 work
3 - Re-engineer how the rear of the fuel tank attaches to the frame

Tank shape is identical so faring fit is not an issue.