I have run the IMS tanks on every bike I have owned, but have never run a Clarke, mostly because of sponsorship from IMS. However, both tanks have their advantages and disadvantages. For instance, as Paul indicated, the Clarke holds more fuel, but sits really high above the frame. Like Paul, I am not sure about changing the plug with the Clarke tank installed, but it is not a problem with the IMS tank.
For my needs, I have settled on the IMS tank that uses the KX250 shrouds and a different pipe configuration. The advantages of this tank is that you get 4.2 gallons that sits really low in the frame (lower center of gravity equals better overall control). This tank is also much more slim than the other tanks on the market, and plug changes are a snap. Like Paul, I really don't have problems with fouling plugs, but put in a new NGK BR8EVX before every race. When you travel 5, 10, or 20 hours to a race, you don't want to get a bad start because of a failure of a $10 part.
Back to the subject at hand, the up sides are:
1. 4.2 gallons that sit lower in the frame than other tanks
2. slimmer tank gives a better feel.
3. I like the looks of the KX250 shrouds better than the KX500, and graphic options are endless.
4. The new pipe required with this tank, is stronger than anything else on the market, period.
5. the new tank uses the bottom radiator mount on the water pump side of the bike as the top mount, so the problems with the top mount under the seat are gone.
6. On the stock pipe with the old large capacity tanks, some folks have had touble with the pipe touching the bottom of the tank after a crash tweaks the pipe. The new pipe that goes with this tank is routed much differently, so this potential is gone forever.
There are two down sides to this tank/pipe. First, with the new routing of the pipe, the pipe will touch your right boot. This was weird a first, but after just a couple of hours riding, you will never notice it again. The second is the cost, as you need to purchase the tank, shrouds, and pipe all at the same time. However, if I were running the old IMS tank, and needed to replace my pipe, I would swap to this pipe anyway because of the added strength of this pipe.
In a nut shell, if I had it to do all over again, I would still opt for the package with the new IMS tank, KX250 shrouds, and pipe, as the advantages far outway the cost of the kit.
Good luck in your quest.
Rick
