IMS Fuel Tank / WR400F Carb issue

Bought 2 new Ty-Davis 3.1 Gallon IMS tanks for My WR and YZ 400's this past weekend (Tired of having to pit for fuel during the GNCC's). Both were a pain in the butt to install because of the right side petcock and the Shrouds don't fit up as they should. (Had to remove the FMF POWERBOMB on the WR because the fuel line from the petcock was 2mm away from the header....) anyway once installed and the fuel lines run the YZ does fine, but the WR was shutting it's self down constantly. I checked the fuel lines for the possibility of a Fule line collapse, but found none. To rule out carb line clogging, I rerouted the two upperhoses to the airbox..... Retested, 20 minutes later the damn thing shut down again. This time it would re-light then die.... This went on for 30 minutes....Now having become extremely pissed off....I pulled the remaining lines from uner the bike, inspected them for blockage (None Found).....

Just for the hell of it I decided to blow through the lines and listen for air escaping from the lines in the air box....The lines were clear....I then re-routed the lines back between the swing arm, and attempted to re-light the beast.....Dammit it fired up and I rode the hell out of it for the 10 miles back to the trailer with no problems..... WHAT IN THE HECK IS UP WITH THAT......

It appears that the damn thing vapor locked, I have never seen a Yamaha do that before.... This is the second time in the last three rides that the WR has done this....The last time was at another location, I got fed up and took the bike to the wash rack, once all the mud was removed the damn thing ran like a raped ape.......

Any Thoughts ?

Bonzai :)

Is the fuel cap vent and hose clean and clear? I have seen bikes at work with the problem you've described, (mainly road bikes) and it has been blocked cap vents. Worth a look, but if you run the same cap on both your YZ and WR tanks then i'm stumped.

I also thought so in the beginning. I initially had one of those new breather hoses with the little cap on it. I removed it and replaced it with the stock cap and vent hose that I had been using on my YZ. It died again. I physically checked the vent system to ensure that it was clear and functioning properly..... This is a good mystery.

This evening I'm going to replace the last two hoses on the carb (All will be new then. I'll also drop the bowl and make sure I don't have a piece of trash floating around and intermittently blocking a jet.


Bonzai :)


Don't know about IMS but the Clarke tanks come wrapped in Glad Wrap. Could be a floater in the tank that eventually gets wrapped around the screen. Turn it on reserve to get both screens to draw.

Kaze, Two days and no response? This one got you stumped? Curious to know the problem once you figure it out, good luck.

I know this is wierd, but it happened to me. I put an IMS tank on my old 98' WR400 back in 99' and had the same condition you described. No rhyme or reason. It would run, then not run (left turns only :D ).

Turned out my decompresion actuator cable was over stretched in the frame loom by the oversized tank and opened the exhaust valve only on left turns. Could your unit be doing this too ? :)

Does the bike lock the rear wheel in gear when it dies ? Or does it run on ? Try flicking the decompression lever at speed when it dies. This, by accident, is how I figured out the problem on the 98'. Just for grins, pull the tank and inspect that cable and lever for play and/or blockage. :D

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