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Fuel pressure regulator


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robster
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Dec 13, 2014, 2:48 AM

Post #1 of 13 (1046 views)
Fuel pressure regulator Sign In

Hi, i own a classic car, with SU carb. i noticed some amount of fuel underneath the carb coming from the overflow valve, i was thinking the fuel pressure might be overcoming the fuel needle regulator, which i already replaced with viton tip.
is it advisable to use a fuel pressure regulator? thanks--Bob


Tom Greenleaf
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Dec 13, 2014, 4:33 AM

Post #2 of 13 (1033 views)
Re: Fuel pressure regulator Sign In

Whatever this set up and vehicle is do you even know what specs are suggested?


Carb suggest a mechanical fuel pump usually which itself will only pump so much pressure and if electric you choose the spec when you get one if in line or however done on this thing.


"Needle Valve Regulator" really is if like carbs do just an on/off flow needle to seat that IMO isn't too fussy about pressure just allows fuel into carb bowl as floats drop in the common carbs designs. 4-6 PSI is about right for most.


In short you need to know what it is now and what you require. The leak for now is probably needle valve I would call it is way off adjustment or can't "seat" to shut off flow,


T



Discretesignals
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Dec 13, 2014, 8:02 AM

Post #3 of 13 (1021 views)
Re: Fuel pressure regulator Sign In

Would help to know the year, make, model, and engine size.





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robster
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Dec 13, 2014, 8:12 AM

Post #4 of 13 (1012 views)
Re: Fuel pressure regulator Sign In

i have a 1972 classic mini, it has a manual fuel pump, i mean the pump is attached to the engine. (not electronic), sorry im new to cars.
i am tempted to use those Gum out fuel system cleaner but im thinking it might eat up the viton rubber tip and may start a leak again.

and to add, i got a chance to see the carb float and didnt see any way to adjust it.

thank you


Tom Greenleaf
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Dec 13, 2014, 8:24 AM

Post #5 of 13 (1010 views)
Re: Fuel pressure regulator Sign In

Helps to know what it is but I personally don't know these cars well at all newer or older. Engine mounted fuel pumps are about all limited to the pressure of a spring inside them not elsewhere so really doubt this is too much pressure.


You may not see any adjustment for float/device for these whacked type carbs or even more universal ones but rather bend tabs having the setting #s at hand and probably need to weigh any float if not recently known OK it it's heavy it will sink and fuel will flow like it need to have more and doesn't so there would be your fuel leaking.


I can't possibly come up with specs for this carb exactly or even a good guess. You would at a minimum need carb part #s and then find the specs and settings for it. Rebuild kits usually come with that but no promises.


If you or someone VERY familiar with the carb is available you can take top off of most and watch a float rise in fuel and push needle valve shut before it's too full. A lost art for many now to set and adjust one with zero info for exact carb.


Again - IMO your leak isn't from pressure but a problem with fuel not being shut off for any reason right at the carb,


T



Discretesignals
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Dec 13, 2014, 8:25 AM

Post #6 of 13 (1006 views)
Re: Fuel pressure regulator Sign In

We don't have the vehicle here in the states, so access to service information is nil.

Is this SU carb something you would find on a motorcycle?

If the carb bowl is overflowing, was the seat replaced along with the needle? How much trash did you find sitting in the carb bowl? The float could be leaking allowing it to sink and keep the needle valve open.





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(This post was edited by Discretesignals on Dec 13, 2014, 8:28 AM)


Tom Greenleaf
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Dec 13, 2014, 8:58 AM

Post #7 of 13 (1002 views)
Re: Fuel pressure regulator Sign In

We are following each other around with a few here DS - no problem. I do think a few of these did get legally sold to the US new back then along with some other impossible to fix British Leylands cars and more.


Carb probably is like for a motorcycle. Has to be in need of a total redo probably every 5-10 years at least if used! Whatever type float and bowl is probably full of junk. Rust mud will become chips of rust foul up the show and floats -- doesn't matter if brass, plastic, a composite or what will absorb weight or hollow brass ones leak thru a pinhole to solder after dried and set again.


One common spec I already mentioned was to weigh them. When not part of the spec you get a measurement of when it will float or perhaps some sight glass on the side but doubt it on this.


The end all trouble is if you had a brand new whole carb at the ready you still set it to the car once installed for fast idle when cold and idle when warm. Gets worse - some were made (general for cars and vehicles) such that you changed them for Summer and Winter or long term use in High Altitude or not OR if another country for the fuel quality available could be in the cards.


This is where you need some real hands on experience for this. Rust mud and chips will usually (if any) come out with a magnet. Carb cleaners should be fine to use to clear any ports up to fine wire and blow them thru here and there knowing they are open and work properly.


It's gets trickier yet. Rest of total tune-up and how good engine is as a whole must be known OK before you get accurate settings on a carb or it's a game of ping pong to get them to run as intended,


T



Hammer Time
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Dec 13, 2014, 9:06 AM

Post #8 of 13 (997 views)
Re: Fuel pressure regulator Sign In


Quote
Hi, i own a classic car, with SU carb. i noticed some amount of fuel underneath the carb coming from the overflow valve, i was thinking the fuel pressure might be overcoming the fuel needle regulator, which i already replaced with viton tip.


I don't know but it really sounds like somebody is over thinking this situation. There was no mention of the engine flooding or running bad. I think that factor alone would tell you the carb is not flooding. It may simply have a leak somewhere



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
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Dec 13, 2014, 9:23 AM

Post #9 of 13 (994 views)
Re: Fuel pressure regulator Sign In

Actually not sure if it's even running at all right now. Carb parts replaced or opened still requires knowing it's OK and we don't,


T



Discretesignals
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Dec 13, 2014, 9:42 AM

Post #10 of 13 (989 views)
Re: Fuel pressure regulator Sign In

I don't think I have ever seen an overflow valve on a carb before. Don't think it would be a good idea to have the fuel flowing all down the carb and onto a hot engine. Maybe it is a vent? HT is right, we don't know if the carb is actually leaking or overflowing. Hopefully the OP responds and doesn't leave us in the dark.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


robster
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Dec 13, 2014, 10:14 AM

Post #11 of 13 (979 views)
Re: Fuel pressure regulator Sign In

at first the engine is running fine then probably after few miles the car stalls and i smell fresh gas, i open the hood then gas flows down the overflow tube, it stalls maybe because the excess gas floods the spark plugs.
plugs were pretty dark when i took it off.
will post pics of the carb later


Tom Greenleaf
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Dec 13, 2014, 10:35 AM

Post #12 of 13 (977 views)
Re: Fuel pressure regulator Sign In

OK - It runs then the fuel seen after a stall I take it. Now let's be careful for fire and use some common sense. It would probably run OK or fair cold with extra fuel like a choke does anyway and reject that as it warms. High fuel level in a bowl makes for higher % of fuel to air ratio and would show on plugs.
I think this is going to take finding some exact carb #s and specs that if you have such a car you should want to have anyway.


It's hard not to be involved with old cars in general to quickly know where to get what parts and specifications up to full blown diagrams and factory service manuals if not for you then for another to help you.


#1 for today is not to allow a fire till totally known fixed. Be ready now all the time while messing with it.


Next consider joining a club for these cars as it does fall under the cars of interest IMO and there should be out there with a bunch of folks who live and breathe these things AND know where you can find what!


I'll try when I can to see what I find out there on these if I can but have to some real things too not just be here all the time.


Any more info you find do post it and we'll see what we can come up with for an approach,


T



Hammer Time
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Dec 13, 2014, 12:42 PM

Post #13 of 13 (962 views)
Re: Fuel pressure regulator Sign In

Another thing to consider is many of these carbs uses cork floats and they can become soaked with fuel and no longer float. That will make fuel level too high in the bowl.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







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