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Diaphragm Fuel Pump


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#1 MickC

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Posted 20 January 2020 - 07:45 pm

I have a MK1 and MK2 both with the stock fuel pump,If I have empty carbs and need to get fuel to the MK2 It takes ages on the starter (shorts bursts throttle open) to  get fuel through,the other day I went to start the MK1 (tank was off for about 6months wouldnt start and had other things to do) when I opend the fuel tap fuel flowed straight away and carb filled and the sucker fired straight up ( I have a inline filter on both that I can see fuel flowing)so as the MK1 is flowing without the starter going I take it the diaphragm has gone?

Any thoughts anyone.



#2 dablik

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Posted 21 January 2020 - 09:10 am

Good chance Mick, cos the MK1 can be a pig to start from after an empty tank (just like when ya miss a quick switch to reserve) i normally stick a 10" piece of hose pipe in the tank cap and cover around it with a rag, then give it a good blow to get the fuel moving, you can take the pump apart anyway for a look see, i found this awhile ago on ebay, not sure if will do the job or not though !!

 

Also the chinese fuel pump has been working fine for me and a few others..

 

PS check that shop on the ebay link as they have a bunch of materials.


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#3 Studley Ramrod

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Posted 21 January 2020 - 10:42 am

I wudda thought the mk2 pump is tired and the mk1 pump is working fine.  BUT, hard to know about the mk1 pump after only one occasion, you'd prolly need to run it a bit and see if it gets starved of fuel on a low tank.  Or, disassemble pump and lick it. :)


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#4 TKH

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Posted 21 January 2020 - 11:06 am

Inline filter blocked?



#5 MickC

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Posted 21 January 2020 - 03:53 pm

Sorry but gotta correct myself here MK2 has a chinky pump fitted,had a running issue thought that might be it but wasnt,issue was coughing and spluttering since I put the bike back together,only just solved it but need one more test on a road that was a pain to go up,will report when done.

MK2 ran out of fuel a while back went for reserve only to find I had crossed the pipes over that come out of the tank so already on reserve,So MK2 will drain the tank so pump pumping ok.

Fuel filter looks clean only done a few thousand but have another to try.

Mk1 is  getting paint on the tank so while I am doing that I can take pump off and split,not sure about licking it tho Studders.

Studders I thought any diapragm pump if not working like no vacum no engine running then no fuel will flow.



#6 Studley Ramrod

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Posted 21 January 2020 - 04:10 pm

Not really sure, prolly depends on the position of the diaphragm and the amount of fuel in the tank.  Also, there's prolly a good reason why there's an off tap fitted.  I've had fuel in the cylinder when the carb float valve has stuck and tap left on and the pump worked fine.


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#7 oldman

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Posted 21 January 2020 - 05:07 pm

If the diaphragm has gone porous it allows fuel into the vacuum pipe into the manifold from there to the cylinder and you get a hydraulic lock and the engine will not turn over.



#8 Hombre

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Posted 21 January 2020 - 09:41 pm

The diaphragm pump is pressure not displacement type.  With fuel level in the tank above carb float height, fuel will flow past the pump even with the engine stopped until the float needles shut it off.  Fuel in tank below carb float height and the manifold vacuum has to cycle the pump enough to fill the float chambers.  If you run out of fuel, best to fill up and wait a while before cranking.  I found 5 litres was sufficient.  On a 3VD, best to shut off the fuel cock if leaving the bike for a while with high fuel level as the carbs are downdraft and any leakage past the float needles can drain eventually to the sump.


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#9 MickC

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Posted 22 January 2020 - 08:22 pm

What I will do is when the tank is painted I will put say a litre in and see if it flows or needs to be pumped and add fuel until it does flow just for my own curiosity and let you know,busy for next few wekks but will do it when I can and thanks for your help so far. :good:



#10 ChrisG

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Posted 23 January 2020 - 06:09 pm

I fitted an electric one to the Mrs Diversion and it made a world of difference.

https://www.ebay.co....=item3b12abc408


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#11 Bjørge

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Posted 24 January 2020 - 11:37 am

I fitted an electric one to the Mrs Diversion and it made a world of difference.

https://www.ebay.co....=item3b12abc408

 

Quite noisy, though....


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#12 ChrisG

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Posted 24 January 2020 - 03:06 pm

It was when I first fitted it but quitened right down after a few minutes ride, presumably once it had got all the air out. Now you hear it for a few clicks when you turn the ignition on but don't notice it after that.

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#13 Bjørge

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Posted 27 January 2020 - 07:49 am

It was when I first fitted it but quitened right down after a few minutes ride, presumably once it had got all the air out. Now you hear it for a few clicks when you turn the ignition on but don't notice it after that.

 

I could actually hear mine on the motorway at ~60MPH, infrequent loud ticks. I even attempted using rubber underneath mounting bracket, to no avail. Well, have an old R6 pump laying around to replace it in the near future.


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#14 MickC

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Posted 27 February 2020 - 11:26 am

Finally got round to painting tank and starting with empty carbs (put the MK2a jobbys back on) and an empty tank I ended up putting over 2litres of fuel in and nothing flowed ( there was less than that in there at the start of this topic) until i pressed the button,unlike the start of this topic when I turned the fuel on the fuel just flowed through and it started straight up but now it wont so maybe not being used for a year ish maybe the diaphram dried out a bit (dont know if it can)and let fuel through without pressing the starter.



#15 Studley Ramrod

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Posted 27 February 2020 - 04:55 pm

Might just be an airlock Mick.  A bit like when one needs to turn onto reserve but doesn't make it in time, takes ages for the fuel to get through.


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#16 MipeTDM

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Posted 02 March 2020 - 06:41 pm

I also fitted an electric pump as conversion, and it was also very loud in the beginning. Since I mounted it in rubbers it's a lot quiter and I don't notice the sound any more. It is nice the pump can push the fuel trough my fuel filter when the bike has been standing for a while. After that, it fires right up! With the original diaphragm pump that was not so straightforward.




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