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Hi,
I suppose I can now claim to be a real SU family member as I have seen my carbs pouring gas onto my exhaust... Great experience indeed! But I don't wan't to drive 50 miles back home like this. The car is now stuck in the countryside.
I've read what I found on the forum using the search, & I dont understand what I could have done wrong. I'm running a B20B with freshly rebuilt SU's (Except rebushing) & a Pierburg pump (Probably aftermarket since I got it on a B18A)with DIY pre-pump filter. I don't suspect my brand new float valves to be leaking. The bowls are clean. Fuel comes out of BOTH vent holes. So I'm suspecting the pump is at fault.
I tried to softly hit the pump wit a screswdriver, which made the leak stop for a few minutes (even at higher revs). It came back after a while when idling. I'm planning to mount another (used) fuel pump to at least drive te car home, assuming the pump is putting to much pressure on the line. Has this happened before to some Pierburged cars? George seemed to be a Pierburg/SU combination fan in one of the posts I read, & fo the last K miles miles I agreed. So can a pump all of a sudden increase its pressure or is there anything I forgot to think of & will make my efforts useless? Should I bring something else with me on my "bring the car home" operation?
Thanks for your help!
Séb
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When you say you have freshly re-built SU's, what has been replaced? There are two types of float, old style where the arm is metal, hasn't been available for years. Or new style, where the hinge on the float is made out of the same material as the float itself.
If you have the new style floats, you need the matching lids. The geometry is different. You'll never persuade new style floats to stop leaking with old lids. I've found new lids, new floats, and the Viton tipped valves to cure the leaking problem.
Note the Viton tipped valves are slightly bigger than the originals, but it's not a problem.
Pierburg fuel pumps are OEM.
Regards
Pete
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Pete,
I have made a standard rebuild on my SU's, i.e. the rebuild kit form CVI (without re-bushing: valve, jets, gaskets & I bought 2 needles as well). Nice kit, all needed parts were there & it's been doing great for the past 1'500 miles. That's why I'm puzzled the problems arise now...
I have kept the old floats (with metal hinge), so no worries there. What is really strange is that both carbs leak. So if the floats are at fault, they would have gone bad both at the same time. Can you buy this? That's why I was thinking of the pump... Moreover, I already performed matt b's test (blowing through the valves with the lid upside down) & the valves seem perfectly tight...
Anyway, a good valve cleaning will do no harm.
Tonite is THE night: "bring the car back home" operation is scheduled for 6 pm till ??? I'll have a small fire ext with me. Will report to you tomorrow!
Cheers!
Séb
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I'm with the others in the float valves as the problems rather than the pump... I figure, at most the pump is putting out 6psi or so, and the float valves should be good up to 10 or so psi. Just a guess on that though.
I don't know how much you like the taste of fuel, so you might bring some fresh now fuel line (1/4"ish) for testing the float valves. Easiest I've found is simply to take both float covers off. Leave 'em right side up such that the floats themselves fall, and blow through the fuel inlet pipe. You should be blowing air through both float valves. Then turn the whole thing (both caps still attached with fuel line) over (such that gravity forces the floats onto the float valves) and blow into that pipe again. If you can blow ANY air through the valves with just gravity holding the floats on them, they're gonna leak. Clean 'em.
It is my experience that new float valves leak as frequently if not moreso than used ones. I can't count the number of times I've bought new float valves only to have them leak and back in go the trusty old valves before I even go for a drive. Never throw away old parts that work...unless you've got plenty of extras.
Oh...and of course, the first thing you do is to tap the top of the float covers with a nearby rock or wrench or bolt or whatever. See if that stops the leak. I have a float valve on my Jaguar that leaks every time I start it cold. Its just become standard procedure to be ready with a large bolt as soon as I kick the pump on.
Good luck with it, and get that small fire extinguisher someone suggested. I never leave home without one in anything with SU carbs...and/or Lucas electrics.
-Matt
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posted by
someone claiming to be Ron kwas
on
Mon Oct 28 02:30 CST 2002 [ RELATED]
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Séb
It's important not to forget to install the spacer between pump and block when replacing the pump...this reduces the actuation lever excursion and thereby the pressure...I really don't see how the pressure can all of a sudden increase if you installed the spacer and haven't changed anything. It just sounds like the OE bowl valves leaking (common phenomenon).
I'm a big advocate of installing Grose bowl valves and a post pump filter...in my experience it doesn't take much at all in the way of contamination to hold open the OE bowl valve (you don't mention which type you have)...and a post pump filter is cheap insurance...I prefer the Grose-bowl valves which use a double ball bearing for sealing instead of the conical neoprene...I do believe George and I dissagree on this, but (with a post pump filter) I have yet to see these leak on ANY of my cars...and that is the satisfactory result I am looking for!
To get the car home, I suggest you remove the bowl caps, inspect for / and remove any particulate contamination from bowl sump (either side of jet feed), also blast some carb cleaner through the bowl valves to flush them, and install a post pump filter (those inexpensive, see-through VW ones you stick in between a cut fuel line seem to work just dandy). Reassemble, start, and doublecheck before taking that long trip...a cheapo little fire extinguisher might be a good investment right about now!
Cheers
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Driving to work last Wednesday I encountered a long line of backed up traffic leading up to a towering column of smoke surrounded by fire engines. As I eventually got by the source I saw it was a severely burnt MG-TF. First thing I thought of was overflowing SU carbs...
I guess you've driven the rebuilt carbs for a while with no problems prior to the spate of overflowing from both carbs? Otherwise I would suspect something amiss with the float bowl level adjustment. It only takes a tiny amount of junk to prop a float valve open, but that -usually- only happens on one carb at a time - not both. Once the valve is stuck slightly open, hwever, the (over)full condition of the float bowl keeps the float valve tightly closed on the bit of junk, and it can be hard to clear. A quick fix is to pinch off the fuel line between the carbs and pump (carefully - don't damage the hose) for a bit with the engine idling until it begins to stumble. Then release the pinch and the empty bowls will refill in a rush and swoosh the offending particle past the jet and into the bowl, where it is harmless. Until enough builds up to block the jet intake, that is...
Since both are leaking at the same time is certainly sounds like the pump. Mechanical pumps put out pretty much the same pressure at idle as the do at higher rpms. The lever pulles the diapragm against a spring, and the spring pulls the diapragm back again producing the fuel pressure. If the carbs are not taking much fuel in the level just stays that way for a bit, barely ticking of the top of the cam lobe. It is the force of the spring vs. the size of the diapragm which results in the design fuel pressure. At higher rpms it just has more frequent opportunity to push the lever back up, but that doesn't result in higher pressure. A fuel pressure regulator might help, but those are very sensitive to grit as well.
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posted by
someone claiming to be Ron Kwas
on
Mon Oct 28 10:55 CST 2002 [ RELATED]
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...and the Lucas equipped vehicle can be considered to have mulitple possible sources of electrical selfignition!...a pretty risky combination!
...cute and probably very effective leak stoppage/particle clearance technique!
Cheers
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Ron,
Thanks for your quick answer, altough I would have preferred to hear bad things about my pump instead of my float valves...
I of course took the covers off & didn't notice any dit in the bowls. What made me feel happy about my valves was that they are k miles old & that when I blew through the gas inlet on the front cover while holding the floats against the covers, there was no way to get air passing through. Maybe I don't blow hard enough??? That's why I suspected the pump... Or gan gas pass where air can't???Any idea about this situation?
Thanks again!
Séb
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I've been having problems with my front SU HS6 for some time now dribbling
at high rpms. I have tried a number of different float valves, both
Grose Jet and neoprene OEM valves, and the back carb is fine. I suspected
pressure problems but when I checked the fuel pressure it was rock steady
at 3 psi, which is exactly what it is supposed to be. At speeds below
3000 rpm I don't get any leakage but I DO when I wind it up and I have not
been able to rectify the problem with the current carb, which I rebushed
around Christmas 1999. Got about 3000 miles on it now.
Since the fuel pressure is controlled by the spring that backs up the
diaphragm, I don't think a stroke increase could change the pressure but it
does put more stress on the pump and make the cam push the lever at the wrong
place so I would NOT operate without the spacer.
(In a diaphragm fuel pump the lever actuates the suction stroke and the
spring pushes the fuel out on the discharge stroke. So the spring is the
sole mediator of output pressure. It may be possible for the spring to
become unseated with an excessive stroke and thus be effectively operating
in a shorter position in which case it might put up higher pressure but I
think this is pretty unlikely.)
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma
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Well, the thing is I HAVE the spacer... Maybe it's just part of the SU fun to have some leakage, altough I don't think a burned down amazon is part of any fun... Well, I'll try with another pump & if it doesn't work, i'll go for new valves... If this doesn't work I'll go for a New Beetle! NO, Just kidding, i'd never let my 121 go!!!
Could the float level be a fault?? What is the proper setting anyway?
Tanks!
Séb
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For the HS6 the float level is measured with the float lid upside down
and the distance from the top of the float to the bottom of the lid
is 4.8 mm or 3/16".
For the HIF6 the float level is set with the carb body upside down the the
bottom of the dip in the bottom of the float is 0.5-1.5 mm (.020-.060")
above the bottom flange of the carb.
Too high a float level (with the carb right side up) would certainly
make it more prone to flooding but if it is overflowing the float
chamber lid (HS6) then it is more than that.
Another problem I have had is insufficiently tightened float valves
working loose and leaking past the gasket ring. Currently my problem
only occurs at high rpm so I suspect it is the vibration of an unbalanced
engine shaking the float too hard.
BTW my Pierburg mechanical fuel pump blew the diaphragm on a fuel pressure
regulator and nearly drowned my engine in gasoline. Pressure never exceeded
3 psi as nearly as I can tell so I conclude the regulator was defective.
Fortunately no fire.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma
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