Previous photographs in topic 379 "Extra Gas" show the mounting method I used for an XR tank.
This method was used on two bikes, but it involves complicated shaping of pads from rigid foam
material that is hard to find. Substituting with the closest available foam material was workable,
but posed three problems. First, there was the trial and error shaping and fitting of the foam, and
even with my best efforts there were imperfect fits. Second, as the substitute foam compressed
over time, a problem developed with maintaining a clearance gap for the fuel tap on the XR tank.
Third, dirt could accumulate around the various chunks of foam and was impossible to clean off
without removing the tank.
When it came to mounting a tank on a third bike I thought there had to a better method,
one that used easily obtained materials, maintained clearances, did not require trial and
error fitting, and did not allow dirt to accumulate. Also, I wanted to be able to make up a
kit of mounting hardware that could be fitted to any CT quickly and accurately, using only
the tools I travel with. The key was a different mounting and support system for the rear
of the tank. It was used to fit an XR tank to Arthur, the 110 I bought in Australia for my last
big trip over there. I was able to fit Arthur's tank using prefabricated kits of parts, one for
the tank and one for the ignition, in about an hour. Inspection at the end of the trip showed
no problems with the method.
Here's the tank fitted.

1. ELECTRICS
Relocate the ignition switch. Fabricate mount from mild steel or aluminium.

Extend the four ignition wires. Cut existing wires about midway, staggering the cuts. By
doing this, two big bumps at either end are avoided, making clearance between tank and
frame easier. Use heat shrink on all eight joints, and give extra protection to the wires by
slipping a length of bicycle tubing over the whole lot as in the photograph below. The tubing
can be secured with cable ties at either end.
Below: the mount, with a small tang to stop lock from turning Here the holes for handlebar
bolts are still to be drilled. To make the lock hole I drill multiple small holes then file out to fit.

2. FRONT TANK MOUNT
6mm threaded rod is used in the front tank mount, as I could not find a 6mm bolt
long enough. A benefit of the rod is that it can be cut to the exact length, and unlike
a bolt can be inserted and withdrawn from either side.

A couple of rubber bungs are drilled through and used as spacers. I got these from
a home-brewing outlet. Use a drill press, 7mm drill, go slowly and enjoy the smell.
Later they will be cut to the correct length, as with the ones on the rod.

Here's how the threaded rod and bungs relate to the aluminum and black
rubber mounts on the tank

Two brackets for the front of the tank, cut from 4mm aluminum. Tried steel ones but they
were unnecessarily strong and costly as I had to get someone else to cut them out.
The aluminum can be cut with a hobby type reciprocating saw such as a Dremel using
a standard wood-cutting blade, though a metal saw would be easier - just didn't have one.

I didn't think it the wood blades would work, but here's the proof. Managed to cut
out three brackets before needing to replace the blade. These brackets are the
hardest part of the whole job - not the cutting out, but getting the shape right.
They need to be exact, otherwise the tank will not sit correctly or may not have enough
clearance at the front or back. The grid they are sitting on (above) is marked in 10mm
squares - this could be used as a guide for laying them out.

3. REAR TANK MOUNT
Exhaust clamps, steel rod and garden hose. What else would you use to make the rear
mount? My CT downtube is 51mm diameter and luckily there is an exhaust clamp exactly
that size. Slightly bigger wouldn't be a bother, though. Weld the rod to the bracket, heat up
hose and force over rod as cushioning. The rod on either side of the clamp forms the tank seat.

Clamp fitted to downtube. Leave the clamp loose until tank is fitted so that it can be slid
up or down to get the required tank clearances.

4. FOAM PADS
Look like knee grips off a Triumph, but these are foam pads that are glued .....

here .....

and here, to fill the gap between tank and frame. Make sure the throttle cable run is
not restricted and the wiring harness still has clearance when the handlebars are turned.
The aluminum brackets are fitted to the frame using the existing engine protector bolts.

5. FITTING
Fit the front of the tank using the rod. Cut the bungs so that they are a close fit, taking up
any gaps between the aluminum brackets and the existing tank mount parts.
I use nylok nuts on each end of the threaded rod, or two ordinary nuts locked together.
Just snug the nuts so they are sitting lightly on the outside rubbers, don't clamp the
tank tightly - it should still be able to move a little.

Check there is clearance between the tank and the steering head.

Check clearance between the tanks. Slide exhaust clamp up or down downtube to adjust
the tank, remembering to check that the cross rod is still in a suitable position to act
as a seat for the tank bottom and is not touching the fuel tap.

Also make sure that wiring is not being pinched and is not stressed when the
handlebars are turned.

6. TIE-DOWN
With the front and rear mounts in place, the tank can still lift at the back.
To restrain this, the screw that on the XR was a seat-fixing point is used ....

along with a small tie-down strap and solid metal ring.

Like this at the top ...

And below the tank the strap loops around downtube.
Tighten just enough to hold tank lightly against the rear mount.

Don't forget a breather tube - doesn't do much, but it looks pretty!

7. FUEL MANAGEMENT
With two petrol taps there are nine possible combinations of settings, two of which are
undesirable and will be mentioned later, and four different ways to connect up the three
fuel lines. Here's the way I prefer, regarding the XR tank as the main supply and the CT
tank (including its inbuilt reserve) as the reserve supply :
Connect the line from the XR tank to the "ON" spigot on the CT fuel tap.
Connect the reserve line from the CT tank to the "RES" spigot on the CT tap.
The line from the CT main is plugged and tucked in close to the carb (below).
Using fuel from the XR tank :
Top tap ON
Bottom tap ON
Using fuel from the CT tank :
Top tap OFF
Bottom tap RES
Using fuel from the XR reserve :
Top tap RES
Bottom tap ON
Fuel off :
Top tap OFF
Bottom tap OFF
TWO SETTINGS TO AVOID :
1) Top tap ON / Bottom tap OFF
2) Top tap RES / Bottom tap OFF
These tap settings will allow fuel to siphon from the XR tank into the CT tank,
possibly overflowing the CT tank.
Below shows line connections and location of the rear mount in the background.
I fitted an extra inline filter to the XR tank line. On this model bike there is a filter
built into the carb, but an extra filter could be fitted to the CT line as well if you wished.

8. CAPACITIES and RANGE (Range calculated at 3lt per 100 km, typical of loaded and fast riding conditions)
|
|
Liters |
U.S. Gallons |
Imperial Gallons |
Kilometers |
Mileage |
|
CT Tank |
5.10 |
1.34 |
1.12 |
170 |
106 |
|
XR Tank |
9.80 |
2.58 |
2.15 |
326 |
203 |
|
Totals |
14.90 |
3.92 |
3.27 |
496 |
309 |
If you have managed to empty all three tanks, XR main, CT, and XR reserve,
and still haven't got to where you are going, there is one last hope. The XR tank
has a high spine that can trap a little fuel on the right hand side where it cannot reach
the outlet. Lay the bike over on its left side and this fuel will be transferred to the tap area.
Not much, but maybe enough for another thirty kilometers.
A note on tanks : The Honda XR tanks are from late 1980's models. No doubt
there are many others that could be adapted, but having figured out all the clearances
for this tank, I prefer to stick with it. At 9.8 litres, it is also the biggest that will fit easily.
If you pick one up, make sure it has both tap and cap, as these will cost more than the
tank itself if you have to buy them separately. So far I have bought five XR tanks, and
all but one had a tap that leaked when tested. After a lot of manipulation and a couple
of days soaking in fuel they all came right - perhaps the internal seals dry out if the tank
sits empty for a long time.
Cheers
Bernard (NZ)
