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I have a 85 kz700a-1 it is not quite a bobber yet, I intend on making it one. The gas tank itself is intact, no petcock and severe rusting. Have small holes starting to appear. I don't need a stock tank, would prefer one different, but would like coverage of top part of frame from trippletree to seat. Does anyone. Know what models and years will fit? I've spent a few hours on here searching , can't seem to find anything, so pardon me if it's here already. Is there any aftermarket options? I am new on this site. Any help appreciated. Love this site!

Is the tank installed on the motorcycle? I'm wondering if you have the rear tank mount bracket.
As for other tanks >> direct fit would be the KZ700, KZ750-L3 & KZ750-R1 GPz. these might be hard to come by.
You might be able to use a KZ750E tank with some fettling of the rear mount, but I really don't know.

ps: a KZ700-A1 should be a 1984 model & I wouldn't cut up or ruin one of those.

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For a bobber you may want to consider a 750 LTD tank. Some fabbing may be needed for the rear mount but it's a bobber so that shouldn't be an issue.