TMax Fever

The Yamaha T-MAX is susceptible to a disease where it won't restart in hot weather. Mine developed the disease and I thought that it was a battery problem. I was wrong. This is everything that I know for sure about T-MAX Fever: In essence it is "The bike will start after a few hours. Go and buy an endoscope"

(This relates to the XP500, I don't know if any of it holds true for the newer XP530)

• If you turn the ignition on while the stop/run switch is set to run, then the fuel pump should run for 2 seconds. You can hear the relay click behind the headlamp, and you can hear the fuel pump run under the front of the saddle.
• During a bout of T-MAX fever the relay clicks but the fuel pump doesn't run.
• Whatever the problem is, it exists within the fuel tank. I managed to disconnect the fuel line and check that the pump was getting power - it still didn't run until the bike had cooled down for several hours.
• The fuel pump runs all the time that the engine is running. A fuel pressure regulator valve inside the tank directs most of this fuel back into the tank, the fuel line to the injectors should be pressurised to 2.5bar.
• The fuel tank contains a single complicated unit comprising the filter, pump, pressure regulator, fuel level sender, wiring, and connectors.

The motor is on the left next to the filter. The F.P.R is just visible on the right below the main column.

• Yamaha calls this whole unit the "fuel pump" and they don't sell the individual components. They charge about £400 for the unit. The thieving bastards.
• It is easy to get a replacement pump to fit into this unit.
• It is nearly impossible to get a replacement F.P.R for this unit. Polini sells one (part number 1730001) that runs at 3.5 bar rather than 2.5 bar. It seems to have the same dimensions as a F.P.R. from an old Toyota MR2 but that has an even higher fuel pressure pressure.
• During correct operation petrol pisses out of the F.P.R and runs back into the tank.
• If I owned an endoscope I could have checked that this was happening by simply stuffing it into the tank through the filler - I don't.
• On my bike the F.P.R had seized - unfortunately my attempt to "free" the valve destroyed it.

This is what I believe happened:

1. Innumerate environmentalists persuaded everyone that petrol should be laced with ethanol.
2. Galvanic corrosion between the different metals seized the F.P.R.
3. The pump has been working against a solid column of fluid, labouring and cavitating and eventually overheating.
4. The hot pump just about carries on spinning, but won't restart once it's stopped.

I have fitted a new (second hand) unit to my bike, judging by what I've read it's still from the susceptible batch. I might fit a fuel pressure take-off to the fuel line and buy a gauge but that is looking rather difficult. If the pump gets noisy, or if I have fever problems again I will rush out and buy an endoscope and observe the F.P.R. I'll keep my readers informed.

Richard "Everybody's got the Fever" B