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Generalissimo Tea Boy
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Discussion Starter #1
Moved my vacuum pump today from the Africa Queen engine mount onto the frame instead. Last year my bike cut out twice in 10 minutes on a fast dual carriageway in very hot weather. I've heard that this is due to the engine mounting, heating the pump up and causing fuel vaporisation on very hot days.

Anyway, last week I had a repeat where the bike tried to cut out when the weather was very hot so I decided to move the pump. Being lazy I've just unbolted it from the starter motor cover, removed the AQ plate and zip tied it to the frame to see if there is an improvement.

Now waiting for the weather to heat up again.
 

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YEN_POWELL said:
...Last year my bike cut out twice in 10 minutes on a fast dual carriageway in very hot weather. I've heard that this is due to the engine mounting, heating the pump up and causing fuel vaporisation on very hot days...
That's not what I would expect. Is the Mikuni pump a constant pressure pump, or a constant flow pump?

The original is a constant pressure pump, and would just pump more fuel if some were vapourised. However if the Mikuni is a constant flow pump, and relies on the float chamber valve to restrict the fuel flow (not the contradiction it appears to be), then the flow rate could possibly be low enough that some fuel is being vapourised. The level would then fall in the float chamber until the engine cut out.

Iain
 

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Generalissimo Tea Boy
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Discussion Starter #3
That's a good question and 'I don't know' is not a good answer.

I just heard that ideally, it should be mounted somewhere that doesn't directly attach to the hot engine and with the inlet/outlet pipes pointing upwardish for best results. I've done one out of the two as a halfway stage to see if it happens on the next hot day. It's already done more miles than the Honda pump so I'm not displeased with it or anything.
 

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hey guys, where can you buy the mikuni fuel pump from and how much is it? don't need it yet but just in case.
 

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Pleb
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You bad buggers........ looked everywhere for a fuel pump on my Tranny....can you point it out????
 

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Generalissimo Tea Boy
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Discussion Starter #6
Recycler said:
You bad buggers........ looked everywhere for a fuel pump on my Tranny....can you point it out????
Not sure you've got one. It's only for bikes with part of the fuel tank lower than the carb fuel inlet.
 

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Generalissimo Tea Boy
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Discussion Starter #7
Eugen1 said:
hey guys, where can you buy the mikuni fuel pump from and how much is it? don't need it yet but just in case.
Got mine from Africa Queens, a German company. Cost about £50 including post and packing.
 

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Generalissimo Tea Boy
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Discussion Starter #10

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Generalissimo Tea Boy
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Discussion Starter #11
Dilbert said:
Yen
check out http://www.xrv.org.uk/phpBB2/viewtopic.php?t=1469&sid=93beb461541858df09b19cb1bf70ba9e could be we have the same problem or maybe both are caused by air getting into the pump chamber? (Cavitation), mine restarted by bump start, could be that this just forced the air out thereby re-priming the pump? :?
It does sort of sound like what happened last year except I don't understand why your red fuel light would come on, as that's a sender showing fuellevel in the tank. The second time they came on and went off sounds like the self test on my old RD04.

I think mine restarted because the pump cooled back down, which would fit in with your story as well.
 

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My 2 cents...

Yen, after 2 years of messing around with a mikuni pump kit from Africa Queens I've come to the same conclusion as yourself; heat transfers from the engine through the mounting plate into the pump and causes evaporation.

This first started happening a couple of years back in Turkey, continued into Iran then stopped in Pakistan where it was a little cooler. Now it happens on a hot day stuck in traffic and dang is it annoying.

I recently drilled out the pump mounting holes and effectively insulated the pump from the bracket with some rubber hose. However, having not been able to properly test this and about to go to Morocco for a couple of weeks (got back 2 weeks ago - go there, fantastic riding, great people) bought a pierburg pump (model number noted in another thread somewhere) from the helpful guys at www.hansmotors.co.uk. It was only £40 or so and performed fautlesly (thankfully I had left the original relay in place when I fitted the Africa Queens kit).

Interestingly while in Morocco we bumped into 2 French guys on AT's, one of whom had an Africa Queens Mikuni pump, but instead of mounting it on the inside of the bracket with the hoses pointing toward the rear of the bike (as per instructions) it was mounted on the outside of the bracket with the hoses all pointing up. He had had absolutley no issues with it, but I also noted that his bash plate was significantly cut down to allow hot air out more easily. I'll be doing this mod shortly as it makes a big difference to how hot the engine runs when under heavy load.

I had thought of running both the Pierburg and Mikuni pumps inline (as the instructions show you can) but as the Pierburg is so small (and reliable so far) I think I'll just buy another and chuck it under the seat for emergencies.

I do hope that in 10 years time we will not be discussing AT fuel pumps! At only £40 you can buy 2 (or even 3) of the Pierburgs for the same price as a Honda unit and... well... thats my 2 cents!

Peter

PS. If any of you are heading up to the HU meet please feel free to come on over and say gudday, I'm on a K reg green and purple (shudder!) AT
 

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Generalissimo Tea Boy
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Discussion Starter #13
I'll keep everyone informed re my pump.
 

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I'll be there Kiwi and i'll say hello, I am on black @, don't know the reg, i only just bought it, i'll have a blue Khyam tent. Did you see that program about the bike gangs in your homeland? i think they were called the mongrels? Nice guys, type of blokes you'd want as a son in law :lol: :lol:

Bubble
 

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I do hope we are all going to camp together and form a perimeter barracade with our bikes to keep out all those missled G.S boys & girlys!
Speaking to Glynn he tells me they are completly booked up & there is a long reserve list. So if anyone is trying to turn up on spec. ya might not get in. Other surrounding campsites are also very busy this time of year so book now!!
 
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