R8G fuel pressure.
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Thread: R8G fuel pressure.

  1. #1
    Fellow Frogger! Paul T's Avatar
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    Default R8G fuel pressure.

    Hi all,
    I am having a bit of trouble with fuel leaking from my webers after the engine is switched off. I believe I have too much fuel pressure and the needle and seat cannot stop the flow. The fuel is found on the underside of the Webers (lowest point). This also creates another problem being difficult starting due to what I believe to be over fuelling.

    First of all would I be correct in my diagnosis?

    And what would be the cure? I was thinking a fuel pressure regulator and if so what type and maximum pressure.

    BTW both Webers have had a full overhaul by a Sydney based carburetor specialist prior to being fitted. Running a Mecaparts fuel pump.

    Thanks,
    Paul.

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    COL
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    Hi Paul

    I would be checking the needle and seats and also float height even though you have had them overhauled.

    Another thing to check is the fuel pressure with a gauge to see exactly how much fuel pressure is there. (3-4 PSI is right from memory)

    Is the Mecaparts a electric fuel pump? (it maybe supplying to much pressure)

    I had fuel running out of one of my Webers awhile back when the needle was stuck wide open,the fuel just run out what I think is an over flow.
    Regards Col

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    1000+ Posts schlitzaugen's Avatar
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    If your fuel comes out of the carbies with the engine switched off, I don't really understand why you suspect the pump.

    I would suspect fuel sitting in the carbies leaks out through bad gaskets and such, rebuild notwithstanding.

    That said, I would check to make sure the fuel is not actually leaking inside the manifolds and then out because this might mean your starting problem is due to overfuelling, not underfuelling. But you probably checked the smoke on startup already.
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    I agree with Col, also there are two types of 40DCOE originally fitted to the 8G, either early 40DCOE25/26 or later 40DCOE 29/30.

    The 25/26 has a lower float height of 8.5mm to 15mm, whereas the later 29/30 has a higher float of 5mm to 11.5mm. Also note that the float height is measured with the gasket in place.

    It is also worth checking the needle and seat are correct. Original equipment for the 8G specifies a 150 (1.5mm) needle and seat, whereas the more common type is 175 (1.75mm).

    The attached pics also show the way Renault measures the fuel pump pressure, and the spec for the 8G.

    My car has a Mecaparts obtained fuel pump, which appears to be a "normal" steel-top Sofabex with the fuel return blanked. So far it seems to be functioning quite well after circa 20K miles.
    Attached Thumbnails Attached Thumbnails R8G fuel pressure.-dsc08132.jpg   R8G fuel pressure.-dsc08133.jpg   R8G fuel pressure.-dsc08134.jpg   R8G fuel pressure.-dsc08135-001.jpg  
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    1000+ Posts Frans's Avatar
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    Agree with SZ. The Webers have little "sump covers" on the bottom that can leak and hence the fuel on the underside. They will then empty the float chambers and be hard to start cos there is no fuel. With an overhaul the new gasket can sag after a while and all you might need to do is tighten the 4 screws at the bottom.

    After that I would investigate further.

    Frans
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    Fellow Frogger! Paul T's Avatar
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    Thanks guys.
    The fuel pump is a mechanical pump.
    My Webers are marked 40DCOE 29 and 30.

    In the first instance I nipped up the 4 screws at the bottom of the carbies as my first thought was the fuel was leaking from there. I suspect the needle and seat and the gaskets on the bottom of the carbies so I have ordered 2 new gaskets for them. I will check the float levels as Simon suggests. Can't do much until next Friday as work is getting in the way again. However I am taking it to Mount Panorama tomorrow to do some spectating at the Bathurst Light CC Supersprint.

    Took it for a burn today around some of the back roads and had an absolute ball. Can't wait till the engine is properly run in and all the little niggles are fixed.

    Thanks,
    Paul.

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    Paul,
    On Graeme's Gordini I made sure that I got the neoprene type gaskets for the sump plates, similar to pump diaphragm, as I had problems with the previous kits. I got mine from MLP Cars (Mick) and I ask personally for them.

    The previous carbs had perfectly flat faces as well, and as soon as I put the gaskets in they were fine.

    I have also found on Graeme's G (29/30) I run the floats at 6mm and it runs cleaner and is not lean at 7k. With a Fascet pump at 4.0 psi exactly.

    Ray
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    Quote Originally Posted by geckoeng View Post
    With a Fascet pump at 4.0 psi exactly.

    Ray
    FYI, race car runs on 3 psi, which is good enough for 3kms/l. So the pressure can be real low and it will feed what is needed.

    Frans
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    I run my 17TS with 2 X 45 DCOE's at less than 3psi. Not sure exactly what but it is regulated to less than 3. It is fine on the race track. from memory that is what is recommended by Weber else you get splash in the fuel bowl that upsets the level. Well I read it some where and so when I was having trouble with my carbs that is what I did. That wasn't the problem, but I have left it like that so not sure what would happen if I took the regulator away.

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    1000+ Posts alan moore's Avatar
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    I also like 2.5 to -3 psi on DCOEs and also I use 8mm float height. I find the neoprene tipped float valves seal off better than the standard brass type.
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    Hi Alan,
    I like the rubber tipped needles as well. From off-road days. When you are bouncing over rough road it was the only way to stop flooding.

    Had a Weber specialist replace mine a little while back, and put them in my hand after. Took the car back to the workshop put them back in and reset the carbs. And all I need now is to put the "slosh tubes" on the emulsion tubes for tight gymkhana events.

    Ray
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    I found that when the car had not been used for awhile and once started and the fuel ran out in the fuel bowl, the rubber tips had got sticky and would not open. So mine have been replaced with metal needles.

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    Quote Originally Posted by Sunroof View Post
    I found that when the car had not been used for awhile and once started and the fuel ran out in the fuel bowl, the rubber tips had got sticky and would not open. So mine have been replaced with metal needles.
    Different situations need different solutions don't they? No "one size fits all"! Interesting post. I learn all the time!
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    If all the sensible fixes don't fix it (and you seem to have addressed those potential causes), maybe check that the tank isn't pressuring because of a dicky filler cap pressure release spring or a filter with a built in check valve.

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    Fellow Frogger! Paul T's Avatar
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    The fuel pressure pressure is now at 4 psi and sounds like it needs to be lower by at least 1 psi. The carbies are still leaking so it will get new neoprene gaskets and check needle and seat size and float height as suggested.

    I took it for its first good 5th gear run on Sunday of about 50km. It appeared to use a heap of fuel and when cruising it was "hunting". Not sure if this is all a fuel/carbie problem or electrical i.e- points? Still a way to go sorting this out.

    Thanks for all the info and suggestions.
    Paul.

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    COL
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    Hi Paul

    The carbies sound like they are flooding the engine with fuel to me.

    A trip to a dyno is a good quick way to sort out the issues you have.
    Regards Col

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    Quote Originally Posted by COL View Post
    Hi Paul

    The carbies sound like they are flooding the engine with fuel to me.

    A trip to a dyno is a good quick way to sort out the issues you have.
    Thanks Col,
    I will get it to my mechanic who has a dyno and try to have it sorted once and for all.

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    Quote Originally Posted by Paul T View Post

    I took it for its first good 5th gear run on Sunday of about 50km. It appeared to use a heap of fuel and when cruising it was "hunting". Not sure if this is all a fuel/carbie problem or electrical i.e- points?
    Paul.
    Hunting is usually a lean condition at that particular rpm and throttle position.
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    All this stuff suggests the carby overhaul did something or left something wrong.

    That is why I asked what the smoke looked like. Little info corroborated with overlooking answers given here give us little chance of helping.

    I would check progression works in light of the hunting at cruising info. If the shop left some crap in the progression circuit that's exactly what you'd get.

    Much better to do all the work yourself. With "professionals" and "specialists" you pay and do the work twice (at least).

    And before going for neoprene gaskets and stuff, just check mating faces are perfect and there's no distorted stuff. After all these cars worked very well from factory with paper gaskets.
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    Quote Originally Posted by schlitzaugen View Post
    All this stuff suggests the carby overhaul did something or left something wrong.

    That is why I asked what the smoke looked like. Little info corroborated with overlooking answers given here give us little chance of helping.

    I would check progression works in light of the hunting at cruising info. If the shop left some crap in the progression circuit that's exactly what you'd get.

    Much better to do all the work yourself. With "professionals" and "specialists" you pay and do the work twice (at least).

    And before going for neoprene gaskets and stuff, just check mating faces are perfect and there's no distorted stuff. After all these cars worked very well from factory with paper gaskets.
    My 17 TS has two X two 45 DCOE's that were used to replace the fuel injection by previous owner. I had a similar problem and when I compared the progression circuit to that of a 12 G and Alpine 310 I found that my carbs had only two progression holes compared to the 12 G/Alpine which had three. I also looked at Al Moores carbys and they also had three so we drilled another hole in exactly the same place and size and fixed the problem. In the case of my car I am still running on progression holes until 2800 RPM or almost 100 kph in top gear. In other words with 12G jetting the mains don't come in until nearly 100 kph. This is normal for DCOE Webers as far as I can understand. The whole long saga is on here some where. I could probably still do some fine tuning because if I need to run say in traffic at 2,800 rpm for a while it is still a bit hesitant. But I have been able to live with that. If I didn't have a number of other cars to play with I might be tempted to play a bit more.
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  21. #21
    1000+ Posts schlitzaugen's Avatar
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    Later carbies had five progression holes, so I take it your problem wasn't only yours. The evolution is explained in John Passini's book.

    But my suggestion is that there might be some crap left who knows where after the overhaul. I had a similar problem with a downdraught DGV and I went down the same path of irrationality assuming that an overhauled carby is in perfect shape. Doesn't have to be, but in absence of proof to the contrary I would not take anything for granted.

    Live and learn. Or not.
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    Fellow Frogger! Paul T's Avatar
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    I removed one of the carbi tops this morning to check the float level. Simon suggests the float level for my Webers (29/30) should be 5 to 11.5mm. Mine measured 5.66 to 14.08mm so one problem found. I removed the needle and seat looking for a size stamping but nothing to show the size so I'm still in the dark there. It is running a bit rich looking at the black smoke on (hot) start up so the jets might need to be changed. As I am a complete novice with Webers I am not confident to tackle it without some professional help plus tiny parts big fingers.
    R8G fuel pressure.-dsc_5453.jpgR8G fuel pressure.-dsc_5454.jpgR8G fuel pressure.-dsc_5457.jpg

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    1000+ Posts Wildebeest's Avatar
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    Quote Originally Posted by geckoeng View Post
    Hi Alan,
    I like the rubber tipped needles as well. From off-road days. When you are bouncing over rough road it was the only way to stop flooding.

    Had a Weber specialist replace mine a little while back, and put them in my hand after. Took the car back to the workshop put them back in and reset the carbs. And all I need now is to put the "slosh tubes" on the emulsion tubes for tight gymkhana events.

    Ray

    Ray,
    I've been holding off posting in case someone else queried your "slosh tubes". It would appear I'm the only one out here who doesn't know what you are about?

    I recall seeing at the speedway a weber'd midget with what looked like extensions fitted to the emulsion tubes. They were out flush with the air horns/trumpets. Was I on the right track [no pun]?
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    Quote Originally Posted by Paul T View Post
    I removed the needle and seat looking for a size stamping but nothing to show the size so I'm still in the dark there.
    That needle and seat looks like the "generic" type found in Fuel Miser type kits, with a "rubber" needle. The Weber seats have the number stamped on the circumference. 150 = a 1.5mm orifice in the threaded part, 175 = a 1.5mm orifice, the shank of a 1.5mm drill can be used to check its size.

    I've attached a pic of a 175 stamped Weber seat.
    Attached Thumbnails Attached Thumbnails R8G fuel pressure.-dsc08163.jpg  
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    1000+ Posts geckoeng's Avatar
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    Mr Wildebeest,
    How are you ??

    With reference to the "slosh" tubes, Frans had a good writ up in his one thread.

    Two new racecars in NZ entry #350

    This is almost exactly what I have done for years.

    Take Care,
    Ray
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