Update 11-25-06: I have removed the tank completely, and it will eventually go into the trash, since it is well on the way to self-destruction due to repeated contact with the chain. If you buy one of these, ALWAYS check the tank mounts after any fall or lay-down on the left side of the bike, to make sure the lower inboard edge of the tank is still clear of the chain. Because of this problem I can't in any way recommend the tank for a woods rider, or any competitive racer. It's great for other uses IF you keep a close eye on alignment and the tightness of the mount hardware and also have good "petcock discipline". The rear upper mount bolt into the subframe MUST be loctited and checked routinely, or it can come loose in the most embarrassing and destructive way.
I chose this approach to add additional fuel capacity to the existing 2.1 gallons on my 525 EXC for several reasons:
I wanted at least another gallon to give me enough range that I wouldn't sweat bullets two hours into the ride, wondering when I was going to run dry. The BD tank gives a claimed 1.1 gallons. The Clarke and IMS replacement tanks only add about 0.8 gallons, and frankly, I think they are really ugly. I don't like the phallic bulge at the filler or the way they obscure the side of the engine. The factory MXC tank adds 1.4 gallons, but a didn't want the added bulk on the radiator wings and the EXC seat doesn't match up properly to that tank. The MXC tank is also rather spendy, and it too hides a lot of the engine.
I liked that I could unbolt the BD side tank in a few minutes, plug the fuel line, and leave the tank at home if I didn't need the extra fuel.
I have read good reports on the BD tank, and at $166 it seemed like the best way to go for my needs.
If I still feel the need for extra fuel, I can add an MXC tank later and have a total capacity of 4.7 gallons.
The instructions that came with the tank _seemed_ pretty complete, with lots of pictures and warnings. I found that there are several major pitfalls that await the first-time installer.
The front tank mount is held to the sub-frame with a
long bolt and a special tapered spacer that fits into the cavity in the airbox.
You must drill out the existing threaded insert.
Pitfall #!: The
instructions warn strongly that when you drill out the
threaded insert you must take care to drill straight through the
sub-frame, using a pilot drill first. I was as careful as I could be, but I
still got the upper hole off center and had to file it to get the bolt through.
The problem is that there is a welded seam ridge inside the tube that makes it
very hard to keep the drill bit from wandering off course. I was unhappy with
the situation, as I am sure it has weakened the frame at that point. If I had to
do this again I would remove the sub-frame ENTIRELY and drill it at 90 degrees
on a drill press. Live and learn....
The finished front mount. Both the brackets are
plated steel and very stout, and also rather heavy. I will gladly trade weight
for strength in this case.
Pitfall #2: The rear
mount, showing the three washers required to clear the EXC plastic, as well as
the existing aluminum spacer. The supplied 16 mm bolt is
too short and the last thread pulled off the bolt when I tried to torque
it down (in a later step). I cleaned up the insert in the sub-frame with a 6mm
tap - thankfully it was unharmed - and installed a bolt that was 4 mm longer.
The mount is to be left slightly loose until the next step is completed.
The tank is slipped into place. The upper mount is slotted for positioning, so
after getting everything aligned, drop down the tank at the rear and torque the
upper mount. Note in this picture the shop rags that keep the metal shavings off
the chain.
The fuel line has to go through the airbox in order
to clear the chain and countershaft sprocket. The front hole has to be
positioned very carefully, in order to clear both the frame and the airbox
rubber boot. It must also clear the lip on the airbox cover. I used a step drill
and a piece of scrap steel plate to protect the rubber. Then I drilled the rear
hole as described in the instructions.
The line is pulled through the airbox...
and tie-wrapped to the sub-frame to give room to work
on the filter. BD gives no guidance here...
Pitfall #3:
The recommended fuel hose
routing looked pretty shabby to me, and I didn't like the idea of using
the supplied clear fuel hose at the carb and main petcock, since the wall
thickness was too small to use the original spring clamps. (The clear hose works
fine on the tee, BD petcock and tank nipple since they are barbed fittings. I
did add small nylon tie-wraps for peace of mind.) I replaced the clear front
pieces with 1/4 inch rubber automotive fuel hose, which is the right OD for the
spring clamps.
I ran the front section forward, then looped it up, around, and back to the main petcock to make things line up nicely and to minimize stress at the bends. The hose still clears the choke button and both the idle speed and mixture knobs. I added a large tie-wrap on the clear hose at the point where it exits the airbox to stabilize the new petcock (not shown in this pic, but easily seen in the previous image), and I secured the front rubber section to the clutch hose to keep it off the cylinder.
The BD petcock is a slick piece of hardware and it feels very nice to operate. Recommended orientation is with the Off position straight up, and the On position pointing forward.
Pitfall #4:
There are no instructions concerning the
fuel cap vent. I chose to run a piece of 5/32
vacuum hose forward to the airbox and terminate it at a universal automotive
inline fuel filter. I ran the hose across the top of the tank and through a hole
as shown. When the tank is lifted into place, the hose runs through the ears of
the top mount bracket. The hose is well protected by the tank. I tie-wrapped the
vent hose to the rear mount.
At the lower left - the vent filter is tied to the
sub-frame.
The finished installation.... maybe. Gee, I wonder if that
vent hose will stay on in the brush?
At least the hose lets you safely dangle the cap when
you are adding gas the tank.
SEE UPDATE 05/04/06 at bottom of page!
Baja Designs recommends that you remove the rear
shock and check for interference between the chain and tank, since the KTM
sub-frame is easily tweaked out of alignment. I removed the plastic mud flap and
both shock bolts, and wiggled the shock out between the frame and tire. Here is
the a pic of the rear wheel fully stuffed using a floor jack - I don't think the
wheel will actually go this far with the shock installed - the knobs are jammed
hard against the underside of the fender.
The chain should clear the tank by about 1/2 inch. It
looks scary fully stuffed, but I think that the amount of time that the chain
spends this close is pretty minimal. The BD salesman told me that they have no
seen signs of chain contact, though a lost master link would probably wreak
havoc here! It would be a good preventive maintenance item to check this
clearance periodically, and especially after a major fall. I plan to add it to
my check list.
Tire clearance is ok - this is an almost new Pirelli
MT21 in size 140/80-18. Anything wider just won't work.
This concerns me... is the chain going to contact the
fuel hose? Time will tell... there is no way to shut the fuel off at the tank if
the hose gets torn off!
Side view of the fully stuffed tire. It's a pretty
strange sight.
Pitfall #5:
The side stand contacts the
tank, HARD. No instructions about this situation....
Before and after pics of the side stand mount. Note
the large gap between the stand and the stop in the left image. I fabricated a
wedge from a scrap of 1/4 inch aluminum plate and epoxied it in place with JB
Weld. I was reluctant to weld the steel stop because I didn't want to ruin the
plating, and this solution gives more even contact on the soft metal of the
stand. I have had very good luck with JB Weld and have no doubt that it will
hold up.
The stand now clears the tank.
In conclusion, I am happy with the way the tank installation turned out, but I think Baja Designs needs to refine the installation procedure. I like the ease of operating the new petcock. BD warns that the rear tank must ALWAYS be run dry (or very low) before switching on the main petcock and shutting off the BD petcock, to prevent the main tank from draining into and overflowing the rear tank. The new tank outlet nipple is well below the float bowl, but I have heard no reports of failure to feed the last amount of fuel.
I filled the tank and checked for leaks, but neglected to measure the actual quantity. I will try to remedy that later. I will also post a complete rider's report after my next ride.
Update 08/13/05: Capacity Test:
I drained the BD tank completely dry through the carb drain, added about 1/2 qt of gas to the tank and went for an easy ride around my neighborhood. When the engine started to show signs of starvation, I switched the BD petcock off and rode home on the main tank. I parked the bike nearly vertical by propping a 2x4 under the stand and turning the bar to the right stop. I drained the bowl and front fuel hoses and poured that gas back into the main tank. Then I drained the residual fuel from the BD tank - I was surprised that it was only 6 fl oz (I had expected a lot more). I then filled the BD tank to the very top of the filler neck using a large measuring cup and made some calculations (values are rounded off).
Unusable fuel: 0.05 gal (6 fl oz)
Total Capacity 1.28 gal
Capacity at 95% (to allow for fuel expansion) 1.22 gal
Usable fuel when filled to 95% 1.17 gal
So it appears that the Baja design guys are telling the truth about capacity. It is interesting to see that topping off the tank will give you about 8 more ounces, enough for 3 miles of easy riding. And remember that unusable 6 ounces? I now carry a short length of 5/32 inch vent hose. If I run the bike totally dry, I can still salvage another 2 or 3miles of fuel by pressurizing the tank with my mouth and letting the gas flow back up into the main tank. I would rather do that than walk those miles!
NOTE: When you are filling the tank, the fuel level rises very rapidly when the tank is nearly full. The "95% Full" amount equals 1 3/8 inches below the top rear lip of the filler opening. It would be unwise to fill the tank much above this point if you are going to be transporting the bike - you risk a fuel spill. If you are going to ride immediately, go ahead and top up the tank for the 3 miles that extra gas will give you.
Update: 08/16/05: Ride Report:
I rode about 110 miles of mixed wooded single track, open ATV trails and forest roads, and about 5 miles of highway. All rides were started with the BD full and feeding the engine. I dumped the bike three times, filled up twice, and can now make some solid observations:
There is no sign of chain rub, either on the tank or the fuel hose. There are some slight tire rub marks, but they are cosmetic only. I didn't drop the bike on the left side, so I don't know yet how well the mounts will stand up to a hard hit.
The tank feeds very well, unless the fuel level is low and you are climbing. The carb ran dry at 43 miles while I was climbing a steep forest road. I switched to the main tank until I crested the grade, then switched back to the BD tank and got almost another 10 miles before it ran dry for good.
The petcock is easy to reach and operate. It is important to switch on the main tank and immediately switch off the BD tank to prevent the main tank from partially filling the BD tank. I don't believe running with both petcocks open (after the BD tank has run dry) would hurt anything, but it isn't a good practice. It is definitely NOT a good idea to open both petcocks when both tanks are full!
I topped up the BD tank completely before the first ride to see if it would spill out the vent or leak around the cap - there was no leakage whatsoever, except when I dumped the bike and I got some fuel spillage out either the carb vent tubes or the tank vent (I am not sure which).
I really like the additional range - I no longer worry about running dry. So far I have had no problems other than the installation issues I described above. I was afraid that the tank would look dorky, but the black color blends in and I don't think that it hurts the lines of the bike significantly. I definitely prefer it to an aftermarket main tank.
Update 05/04/06: The vent system as I designed it is a disaster, and a serious danger. I finally managed to ride off with both tanks full and both petcocks turned on. I still don't know how it happened, but by the time I became dimly aware that something was wrong (about 10 miles) I had lost more than half a gallon of fuel all over my chain and rear wheel. It is a miracle I didn't crash or turn myself into a fireball.
The problem is a very serious one if you ran the vent hose down low as I did: the fuel from the main tank starts the flow going and a siphon is maintained until the fuel level drops below the filler cap opening in the side panel tank. So theoretically you could drain almost all of the contents of your main tank onto the ground. I asked around at KTMTalk and there were a few recommendations, all of which I ignored ;) They were:
1: mount a vent eliminator (check valve) on the BD cap and call it good.
2: run a small hose all the way to the steering head and secure it up high.
3: leave the cap vent open to the sky and don't worry about it.
The fuel system has several requirements: it needs to allow air in to replace the fuel that flows into the carb, it needs to allow air out to allow for thermal expansion and flow from the main to the side tank, and it should eliminate (or at least reduce) the amount of gas lost in a fall. Number 1 doesn't allow for fuel expansion to the best of my knowledge. Number 2 would work great, but it is a very complicated layout with an additional fuel hose running over the top of the engine and radiators, and it doesn't completely stop the risk of dumping fuel on the instruments or engine in a fall. Number 3 isn't a good choice, but it's the one the BD engineers made, maybe because it's the easiest and there is no perfect solution.
I chose to restrict the vent openings in both main and side panel tanks. I epoxied over the large (1/8"+) holes in the vent nipples and re-drilled them with a 0.040" drill bit. This still allows plenty of airflow but severely restricts the fuel leakage rate. I then ran a vent hose in a simple arc through a couple of nylon clamps out the back of the bike as shown in the pics:
Now the fuel will go off into space if I am dumb enough to leave both taps on. The flow rate is minimal - I filled both tanks and opened the petcocks and timed the leak rate: about 0.75 gal/ hour. In other words, you would lose maybe a pint in the first 10 minutes of a ride - hopefully you would figure out what was happening within that time frame. At least it would give your riding buddy time to shout "What's that stuff dripping out the back of your bike?!!"
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