First bike a good find

I just picked up a free 1983 XJ 750 Maxim. The only obvious problem was a toasted battery and badly rusted tank. The bike stopped running about 10 years ago and just sat in a guys garage. I added some oil, turned it over by hand, hooked up a battery and rigged up a little lawnmower tank to see if I could get it to run before investing time and money looking for a tank.
Fired right up with a bit of choke and ran strong. Ran it up to third gear in the shop parking lot.
I rebuild a few outboard motors and worked on lots of cars but never bikes.
I've read through a few threads here on what needs to be done but first is a tank. Having trouble finding one. What years are compatible with 1983?
Tons of good info here and I'm looking forward to getting this bike up and running.

 

All years of XJ750 Maxim tanks will fit. All years of XJ650 Maxim tanks will fit, but they are 1 gallon smaller and do not have a fuel gauge. Hogfiddles will be along shortly to add to the list.

 

Here it is:

Pulling together info that I have posted regarding tanks..... sometime I'll even re-write it to make a it a little more coherent and logical. Nonetheless, here's the info. Read through it, and maybe you'll find what you need:
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Just for giggles, I did swap some things around to see how things fit:

1 900rk Tank- does NOT mount onto the xj650 maxim, xj750 maxim, OR xj750 seca frame. The upper mount for the frame reflector contacts the seam edge of the 900 tank before the tank can slide onto the rubber mounts. If the reflector mounts were cut off, the tank would slide onto the rubber mounts, BUT the tail of the tank would still be about an inch too far back and will still not allow the tank to be bolted down.

2.750 Maxim tank - as we all know, the 750 maxim tank is a direct bolt-on swap for the 650 maxim tank. The 750 maxim tank WILL also bolt directly onto the 750 seca frame without any modification to the tank of the frame.

The seca seat will still work on the frame, but there is about a 1" or so gap between the seat and the 750 maxim tank.

The seca side covers will not mount onto the frame as the tail end of the maxim tank aims down at the back and interferes with the sidecover top-front edge.

3. 750 seca tank - WILL physically bolt directly onto the 650 and 750 Maxim frames.

The Maxim seat front edges need to be modified to fit the extra length and steeper angle at the rear of the 750 seca tank.

I did not have time to check on sidecover fit. However, due to the upsweep at the rear of the seca tank, the maxim side cover upper front point should still be ok and not interfere.

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Regarding 650 Seca / 650 maxim

Frames are different, I haven't done a seat-swap comparo, but I have done tank-swap comparo which is here in another forum......

That all said, if I get the time in the next few days, I'll try to do that for you.

In the meantime, a quick solution would be to pull the covers and foam, and the do a Seatpan swap..... The seat mounting is different

The 650 rj tank will fit the maxim frame, but you should use the 650rj triple clamps to allow clearance at the front if the tank.... Otherwise you'll run the fork tubes up against the tank on tight turns
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650rj tank on a 550r

650rj tank is slightly shorter in length, by about 1/4 inch at rear oval mounting hole. However, if the tank is pulled back just that tiny bit it will bolt into place. Doing that though, pulls the front hooks about 1/4" back, which leaves a slightly "loose" fit at the front.

The petcock just clears the valve cover but with enough clearance to not be an issue.

The bottom rear of the tank does interfere with the seat pan's lower front corners but they could be trimmed back and re-shaped a bit to allow the seat token and close again.

The front of the seat is too long, too, but if it is cut back and re-shaped and re-curved I could be made to fit nicely.

All that would be cosmetic changes, and readily do-able.
The only "major" issue will be that the bottom of the cramped edge of the tank touches the top ends of the airbox. Once the tank is bolted down there will be pressure in the airbox. If the airbox is heated and softened, the two "channels" could be formed. I guess the tank could be trimmed, but I think that may weaken the seams and I wouldn't recommend that.

550r tank on the 650rj

The 550r tank is about1/4" too long, PLUS the front mounting grommets are just a little bit too wide for the tank to slide on.

When the grommets were removed the tank almost fits right in place.

However, the lower front edges of the tank interfered with the horns. If those are lowered or relocated, that issue will be easily resolved.

The rear of the tank tunnel interferes with the frame but if the tank rear is raised about an inch or so, it clears the frame. If some makes a riser/spacer to mount the tank just that little bit higher its right in line above the regular rear mount

The issues to really address would be --what to do about the tank grommets on the 650r, and the rear mount. Here are the solutions....

Two things must be done for the front:

1. The big ring on the mount needs to be moved in toward the backbone about 1/4" on each mount to allow the rubber grommets to fit in the slightly narrower tunnel of the tank.

2. Use the grommets from the 550r, as they are slightly less tall AND the have a little bit smaller diameter that the 650rj grommets.

For the rear of the tank--make spacer to mount the end of the tank about an inch or so higher above the original mount.

Long and short of it:

Either tank can fit on either bike with either seat mods and airbox mods to put a 650r tank on a 550r; or, minor alteration to the front tank mounts on the 650r, relocate the horns, and add a riser for the rear mount will allow the 550r tank to fit on the 650r

Dave Fox

 

Thanks for the info. This makes finding a tank much easier.