Non starter for 10

Black Panther/Street Moto, Baghira, Enduro, Mastiff, Skorpion Traveller and Tour.

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Re: Non starter for 10

Postby ralf » Sat Feb 25, 2017 2:10 pm

I have exactly the same problem on my 1995 Skorpion Tour. I put it down to the lack of gravity feed of fuel to the carb, it needing to go via the fuel pump which is vacuum operated and hence doesn't operate until the engine is cranking over on the starter. If you bypass the pump and feed the carb direct from the tank the problem will be solved (maybe!!). However, I believe (can anybody confirm this please) that without the pump the bottom reserve bit of the tank can't be used.
Worth a try ?
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Re: Non starter for 10

Postby edfmaniac » Sat Feb 25, 2017 11:24 pm

Almost everyone ditches the fuel pump immediately if they do much reading on the bike. The starting problems still persist due to super lean pilot jet the factory installs to pass emission standards. The reserve is still available even with gravity feed. I've used it. ;)
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Re: Non starter for 10

Postby breakwellmz » Sun Feb 26, 2017 3:01 am

Why is a fuel pump fitted then?
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Re: Non starter for 10

Postby edfmaniac » Sun Feb 26, 2017 4:13 am

Who knows! Probably some engineer said it needed one when gravity says otherwise. There were quite a few things changed between the the prototype making it's tour around to prospective buyers and the production unit coming out of the factory, fuel pump being one of them. Evidently some of the respectable dealers even removed the pump before selling the bikes new.
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Re: Non starter for 10

Postby Skorpion » Mon Feb 27, 2017 4:30 am

breakwellmz wrote:Why is a fuel pump fitted then?


As I understand it MZ bought the engines from Yamaha that they used in their XTZ660 Ténéré, these bikes need the fuel pump as the tank is lower than the carb's and Yamaha supplied the engine's as a unit that MZ fitted as is.

You don't want lots of fuel pumps laying around your factory do you.

In the UK not all Skorpions were sold with a fuel pump fitted, as far as I know all the white Traveller's were supplied without.
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Re: Non starter for 10

Postby dandywarhol » Mon Feb 27, 2017 1:56 pm

Are you sure it is a pump?? :?:

The SZR660 uses a vacuum operated valve which opens to allow the fuel to go from the tank to the carbs but it doesn't pump it. This eliminates engine flooding and the possibility of a hydraulic lock when the bike is parked up and the possibility of the fuel tap leaking.

I'm guessing all vacuum taps operate this way
Last edited by dandywarhol on Mon Feb 27, 2017 2:19 pm, edited 1 time in total.
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Re: Non starter for 10

Postby Skorpion » Mon Feb 27, 2017 2:09 pm

dandywarhol wrote:Are you sure it is a pump?? :?:

The SZR660 uses a vacuum operated valve which opens to allow the fuel to go from the tank to the carbs but it doesn't pump it.................... :roll:


Never having one fitted, but my understanding it is a pump that works on the vacuum pulses in the inlet tract, just the same as pumps in most small scooters do.
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Re: Non starter for 10

Postby edfmaniac » Mon Feb 27, 2017 2:14 pm

According the literature I read the other night, the SZR needs a pump because part of the tank is actually below the carb bowl. OEM parts houses also list the part as a pump. Everyone that has talked about removing it from Skorpions calls it a pump. Must be a pump. :)

You sure you aren't talking about a vacuum operated petcock?
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Re: Non starter for 10

Postby dandywarhol » Mon Feb 27, 2017 2:20 pm

So, how does it pump with a constant vacuum?
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Re: Non starter for 10

Postby dandywarhol » Mon Feb 27, 2017 2:29 pm

dandywarhol wrote:So, how does it pump with a constant vacuum?


I'll answer my own question - It could "pulse" - not sure about "pulsing" 50 times/second at 6,000 rpm :?

I have a spare - i'll pull it apart sometime
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Re: Non starter for 10

Postby edfmaniac » Mon Feb 27, 2017 5:07 pm

It's probably just a simple diaphragm pump with a one way valve in the right spot. Some rc aircraft engines I had when I was a kid used a fuel pump that worked off of crank case pressure and some worked off of vibration alone. But I'm guessing the Yamaha pump is diaphragm based.
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Re: Non starter for 10

Postby Skorpion » Tue Feb 28, 2017 4:53 am

edfmaniac wrote:It's probably just a simple diaphragm pump with a one way valve in the right spot. Some rc aircraft engines I had when I was a kid used a fuel pump that worked off of crank case pressure and some worked off of vibration alone. But I'm guessing the Yamaha pump is diaphragm based.


Yes just a diaphragm pump, uses the pulses created by the inlet valves opening and closing. :D

I would think low pressure output as only carburetter float valve to stop carb flooding.
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Re: Non starter for 10

Postby breakwellmz » Tue Feb 28, 2017 6:34 am

Sounds just like the fuel pump you find in a garden trimmer.
I was imagining a`proper`mechanical fuel pump. :roll:
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Re: Non starter for 10

Postby DAVID THOMPSON » Tue Feb 28, 2017 3:43 pm

big pump not needed it would just make it piss on your pants leg and put you in danger :smt023 :smt113
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