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Mikuni MX40


sharpness

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Sadly, our MX40, after 15years unfailing, albeit light service has given up the ghost. The on/off switch flashes 3 slow flashes followed by 6 quick flashes which, if its the 6 quick ones that count, not the 3 slow flashes means "fuel pump failure"

We are out for 6 weeks at the moment & at this time of year its not a major problem but will need sorting.

My first thought was to ask member NMEA but sadly it was last October that he was last seen on the forum.

When I switch it on the start up sounds normal, I can hear the fuel pump ticking, it fires up as the nearest rad flow pipe starts to warm but it then stops working after a couple of minutes.

The Mikuni Flow chart suggests replacing the control box, if that doesn't sort it replace the fuel pump, I'd have expected that to be the other way round.

Does anyone have any experience or suggestions please.

Thanks

Steve

 

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I have had my Mikuni MX40 in bits twice now hunting faults indicated by the lights. Both times I couldn’t find anything wrong, but got it going again by disconnecting and reconnecting all the plastic push fit wiring connectors. Mine at least seesms to be susceptible to oxudation on the electrical contacts. On top of the unit is a black box, inside of which are 5 or 6 separate connectors.

 

Worth a try. Good luck.

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The last one I remember that was doing this had a faulty relay in the control box. A new box came from Mikuni and it had a much uprated relay inside so perhaps its a regular fault.

I would caution about taking it apart, the screws strip their threads easily and the paper gaskets all fall apart as soon as you remove them.

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21 hours ago, hider said:

The last one I remember that was doing this had a faulty relay in the control box. A new box came from Mikuni and it had a much uprated relay inside so perhaps its a regular fault.

I would caution about taking it apart, the screws strip their threads easily and the paper gaskets all fall apart as soon as you remove them.

Thanks for that, I'd be reluctant to take it apart, not really knowing what I'm looking for, we don't really need it at the moment & are away for a few weeks yet so I'd have problems having parts delivered. I do however already have a spare glowplug & gasket set that I have never yet needed.  

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  • 2 weeks later...

Sorted.  I spoke to Ed Shiers, he gave me some useful pointers. I had the boards up to check some of what he suggested & straight away found a problem with the fuel supply. It looks as though I knocked/leant on the fuel pipe between the fuel pump & glow plug boss & bent it & so restricted the fuel supply when I was servicing the engine/changing the coolant before we came away. I very carefully bent it back close to where it should be and all is well again. I'll remake the pipe properly when we get home. I remember I struggled with the bottom skin tank hose down in that corner but hadn't realised I'd bent the pipe. Thanks for suggestions. 

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