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 Post subject: Re: 750 Sport run issue
PostPosted: Wed Jun 13, 2018 11:19 am 
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Joined: Mon Apr 16, 2018 8:37 pm
Posts: 16
Location: Finland
model: 750 Sport
year: 1989
Thank for the tips! Have to measure the pump pressure. How much is the original pump pressure value?

I desided to get new fuel lines and the Holley regulator. I assume this is the item people are using? https://www.holley.com/products/fuel_systems/fuel_pumps_regulators_and_filters/regulators/carbureted_regulators/parts/12-804?

Also will check the needle and float level.


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 Post subject: Re: 750 Sport run issue
PostPosted: Wed Jun 13, 2018 3:29 pm 
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Joined: Thu Nov 29, 2007 2:38 am
Posts: 280
Location: UK
model: 907 I.E.
year: 1990
Obito wrote:
Thank for the tips! Have to measure the pump pressure. How much is the original pump pressure value?

I desided to get new fuel lines and the Holley regulator. I assume this is the item people are using? https://www.holley.com/products/fuel_systems/fuel_pumps_regulators_and_filters/regulators/carbureted_regulators/parts/12-804?

Also will check the needle and float level.


The Original FP pressure should be around 5PSI; the replacements I found around for this aplication are all 5-5.5psi.

The issue is that the EFI and the carburated pumps look exactly the same so if in the past there have been any changes in the bike (Tank, pump, fuel delivery, etc) most likely the job was not done correctly therefore it must be rectified.

why would you fit something that should not be there and was not included in the original design? That bike never had a pressure regulator so I dont understand why would you put one when the problem is somewhere else?

Moreover, why would you keep a high pressure in the fuel system if it is not needed? all hoses would need to be replaced with EFI ones or they might blow and I an not sure if I would like that to happen with me on the bike...

instead of fixing the real issue you are putting a patch , but the issue is still there.

I would first investigate the fuel pump, then if is you return line is clogged, then the state of the float valve AND the hight & condition of the float itself (could be pierced and therefore is not floating corectly) ;

the pump should have a part number , in any case the ones fitted on low pressure systems (VWs , Land rovers, millions of other carburated vehicles) should fit, in fact if you look on ebay probably there are 50 vendors selling them with branda like Airtex or Quantum

Online I read that Webers 44DCNF should run @ less than 5psi at idle and a little less while on the road (0.25BAR) so it MUST be very low pressure or it WILL put too much pressure on the floats


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 Post subject: Re: 750 Sport run issue
PostPosted: Wed Jun 13, 2018 5:28 pm 
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paso grand pooh-bah
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Joined: Sun Jul 18, 2004 12:00 am
Posts: 5221
Location: southern Germany
model: 750 Paso
year: 1987
:lol: :truck: someone who thinks like me.
A pressure regulator can be a good thing but just like with the wiring mod it should be done only after it has been verified that everything is in perfect working order. If that isn't done you're only adding another variable.

The return line is working. Obito mentioned that earlier.
What do you mean by
Quote:
Moreover, why would you keep a high pressure in the fuel system if it is not needed? all hoses would need to be replaced with EFI ones
? Of course the fuel lines should be EFI ones or they'll dissolve over time if submerged in fuel but what are you referring to about wanting to keep high fuel pressure?!

I would check the carb first as imho chances are higher the problem is there rather than a past owner having swapped to a wrong fuel pump. If the carb is checked and maybe fixed there's no further need to remove the fuel pump. jm2c


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 Post subject: Re: 750 Sport run issue
PostPosted: Wed Jun 13, 2018 7:21 pm 
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Joined: Thu Nov 29, 2007 2:38 am
Posts: 280
Location: UK
model: 907 I.E.
year: 1990
paso750 wrote:
:lol: :truck: someone who thinks like me.
A pressure regulator can be a good thing but just like with the wiring mod it should be done only after it has been verified that everything is in perfect working order. If that isn't done you're only adding another variable.

The return line is working. Obito mentioned that earlier.
What do you mean by
Quote:
Moreover, why would you keep a high pressure in the fuel system if it is not needed? all hoses would need to be replaced with EFI ones
? Of course the fuel lines should be EFI ones or they'll dissolve over time if submerged in fuel but what are you referring to about wanting to keep high fuel pressure?!

I would check the carb first as imho chances are higher the problem is there rather than a past owner having swapped to a wrong fuel pump. If the carb is checked and maybe fixed there's no further need to remove the fuel pump. jm2c



Maybe I was not clear.

When I got the fuel lines for my current project / SSie-Sport (one day I might tell the story of it... a sort of horror one...) I was specificly asked 2 questions:

- do they go inside the tank?
- do they need to feed an FI system?

I was told the EFi ones are stronger than the normal ones and that the ones that go inside the tank are treated for in/out fuel opposed to the standard ones that are treated only on the inside.

My assumption is that there were 2 types , 1 for Efi and 1 for carbs and the ones for carbs are for LOW pressure only.

maybe I am wrong, anyway, IF (IF!) the fuel pump in question is the EFI version, from the Tank to the carb you will have 3BAR /75PSI (or more!) so the lines need to be specific to withstand that pressure.

Since any Pressure regulator will be stayingf between the tank and the carb, unless you put the pressure regulator inside the tank, you will have 3 bars in the fuel line up to the regulator and I would not like to have that on my bike unless it is strictly necessary (like on EFi engines)

I would add that if taht is the case then maybe it would be whise to remove the jet inside the return or you will have un-necessary pressure also on that one.

Anyway, I think the best is to re-check the whole system, making sure is set as it was intended at the factory and eventually check the pump pressure...

I am of the opinion that something wrong was done in the past and that all problems are coming from there.


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 Post subject: Re: 750 Sport run issue
PostPosted: Wed Jun 13, 2018 9:23 pm 
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Joined: Fri Feb 06, 2009 5:40 pm
Posts: 19
Location: Germany
model: 750 Sport
year: 1988
As far as I know, the fuel pump of the SSie deliver 3 bar. Fuel pumps for the carburators models deliver a much lower max. fuel pressure. I believe the value is something around 0,5 bar.

Greeting Volker


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 Post subject: Re: 750 Sport run issue
PostPosted: Thu Jun 14, 2018 2:56 pm 
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Joined: Mon Apr 16, 2018 8:37 pm
Posts: 16
Location: Finland
model: 750 Sport
year: 1989
What is the floot level hight? 42mm or more? If 42mm without gasket then no ptoblem there. Needle is ok.

Oh and my carb has those plastic floots so can’t use the same values as in weber.doc (50mm)


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 Post subject: Re: 750 Sport run issue
PostPosted: Thu Jun 14, 2018 3:05 pm 
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Joined: Mon Apr 16, 2018 8:37 pm
Posts: 16
Location: Finland
model: 750 Sport
year: 1989
My carb is 44DCNF. Isn’t the original 40DCNF?

Edit: got too much fuel gas in my head and confused the carb type :wacko:


Last edited by Obito on Thu Jun 14, 2018 6:00 pm, edited 1 time in total.

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 Post subject: Re: 750 Sport run issue
PostPosted: Thu Jun 14, 2018 3:25 pm 
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Joined: Thu Nov 29, 2007 2:38 am
Posts: 280
Location: UK
model: 907 I.E.
year: 1990
Shop Manual says 44DCNF and flaoting hight 44mm


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 Post subject: Re: 750 Sport run issue
PostPosted: Thu Jun 14, 2018 7:19 pm 
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Joined: Mon Apr 16, 2018 8:37 pm
Posts: 16
Location: Finland
model: 750 Sport
year: 1989
angelix wrote:
Shop Manual says 44DCNF and flaoting hight 44mm


Thanks! Adjusted to that value. Will see tomorrow when I go for a ride, if the result is good.


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 Post subject: Re: 750 Sport run issue
PostPosted: Fri Jun 15, 2018 11:03 am 
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paso grand pooh-bah
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Joined: Tue Jul 29, 2008 9:50 pm
Posts: 3185
Location: Hilltown,Pennsylvania
model: 906 Paso
year: 1990
generally speaking regardless of the spec the float should be level with the carb top with the needle closed

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