Sunday 11 September 2016

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


  1. Seemingly you can buy replacement Fuel Pressure Regulators in Italy - where they love their T-MAXs.
    They are made by BCR, part number 407050100

  2. I bought the endoscope. There is no problem with the FPR, the pump just doesn't run once it's got really hot. I have changed the motor and had no problems since... fingers crossed.

  3. Where did you get the motor? And how much was? Thanks

  4. I got the pump on ebay, it was about £30. There's a company that makes high quality pumps that are compatible with high ethanol fuels - much more expensive.

  5. Thanks RJB
    I am so frustrated with Tmax fever.
    So you just replaced the pump and not the whole assembly with the float and filter, etc...? Still OK? Bigwheelsturning on youtube did this and still had trouble?
    Did you have have to pull off the whole tail and seat etc...? I am tempted to cut the plastic and pull it straight out.

  6. The story is complicated by the fact that I broke the F.P.R while I was trying to find the fault. I have a new F.P.R and a new motor in the original plastic housing with the original level sensor and wiring. I've had no problems since I changed them.

  7. Yes, you have to remove all the fairings, the seat, the storage box, the mudguard. It takes a while but it's not _that_ difficult.

  8. Hi. Unfortunately, Tmax fever got me the other day as I was riding my ex p 500 through Melbourne's central business district in Australia. I there are numerous reports of Yamaha dealers replacing the fuel pump free of charge in the US although many of these posts date back to 2011. I have contacted Yamaha Australia in order to confirm what they will and won't do to support a loyal and frustrated customer.

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  10. Thanks for letting us know. There's nothing I can do to help, but let us know what happens.