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Well, I thought it was fixed.
It started flooding again today. Not as bad as before I bent the tab on the carb, but still not good.
So I took both carbs off this time, and compared the float levels (which I should have done yesterday). The front one is much higher than where I set the rear one, but it is fine. I lowered the float slightly on the rear one, put them both back on, and now it floods only a little bit. It will start again, somewhat like seems to be your situation Neil, but only if I put the pedal to the floor to get a lot of air in there.
If I take of the hose to the hot start valve on the rear carb, gas pours out (dangerous, I know, because the exhaust manifold is right there), and therefore doesn't bubble up and flood the engine. On the other hand, If I leave the hose on the hot start valve and remove it from the venting filter, very little gas comes out.
first question, should there actually be gas coming out of that hot start valve? I thought it was just for vapour. If liquid gas in the line isn't a problem, could my problem be that the line from the rear carb to the filter is blocked?
Or...could it be that the rear carb is just getting far hotter than it should. Why does it get so hot when I shut off the engine? Is it heat from the exhaust manifold, or does it come from the intake manifold? If from the exhaust manifold, would a better heat shield help things?
Greg
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Remove valve assembly and check for buildup of junk, it can still flow but not allow valve to shut off properly, very common problem.
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posted by
someone claiming to be Rhys
on
Tue Mar 30 17:01 CST 2004 [ RELATED]
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Greg when you say the front carb was "higher" do you mean the float is higher when the carb is inverted? That would mean the fuel level is in fact lower.
What you call the hot start valve is actually a two position fuel bowl vent. It is for air flow, and "fume" flow only. At idle it vents to the charcoal cannister, and at any appreciable throttle opening it vents to air cleaner face of the carb. If the fuel bowl is flooding, fuel will come out of the hose, or out of the vent hole on the carb face.
Do you have a fuel filter - and is it in the hose from the pump to the carbs? If yes, is it above the exhaust manifold number one runner? Remove the filter anyways, and put it in the hose leading to the pump. Don't use one in the hose between the pump and carbs. A filter is simply a resevoir of extra fuel looking to boil. SU's aren't that sensitive to unfiltered fuel, unless the tank is rusty.
You may still have a leaky needle valve. Did you determine what kind you have?
Don't give up yet.
Rhys
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The front carb float is 'higher' when the carb is right side up, so lower when inverted, meaning the fuel level in that carb is higher than in the rear carb.
There is a fuel filter between the pump and the carbs, but it is up front, near the cover where you add oil (name?). Before I had the carbs rebuilt last fall, the machanic in Toronto put an electric fuel pump in. The mechanical one is still there, it just isn't connected to anything. I am starting to think that the pressure might be too high? He said it was a low pressure, high volume pump, good for carbs. It's a Carter pump, with two numbers on it: P61296S and 03F16B. I have been trying to find this on the net in order to discover the pressure, but havn't been successful.
The needle valve, and for that matter the float action, on the rear carb just doesn't seem as free as on the front one. But that may be just because I have it set now so low (when carb is right side up) that there is not very far to go. The needle has a black conical top, and four grooves down the sides. It doesn't seem to be stuck open, though. The float seems to get stuck, however, against the side of the chanber, when I hold the carb right side up and let it fall down. But I doubt it would get stuck like that when the bottom plate is on, because its travel downwards is restricted (?).
Greg
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My experience is that low pressure electric pumps still are too high a pressure
for SUs. The old Pierburg OEM pump is mighty hard to beat and they are still
making them. Not to argue with Rhys, but I have been using filters on both
sides of the pump and not had any problems related to them except when they
get plugged. I am careful to locate them where they don't get too hot,
typically near the oil filler, like yours.
It sounds to me like your float valve may not be closing right. Might be
good to clean it with a Q-tip and make sure that it is screwed in good and
tight with the black fiber ring under it. A 5/16"/8mm or 11/32" socket
works pretty well depending on which size it is.
If you can get by with doing so in your locality, you might consider using
the canister/tubes etc as a donation for the trash. (This probably won't
play in 'fornia.)
--
George Downs, Bartlesville, Oklahoma, Central US
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posted by
someone claiming to be Rhys
on
Wed Mar 31 03:31 CST 2004 [ RELATED]
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Like George says, the electric pumps will produce more pressure than the SU can handle. Most of them run up to 5-6 psi, and the SU wants no more than 3. If the filter is low in the engine compartment it is fine, so right at the discharge level of the mechanical pump is OK.
The geometry of the float tab that actuates the needle valve is important, and the float must not contact the body throughout its travel.
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Ok -- I guess I will hook the mechanical pump back up.
One other thing. When I blow into the fuel line on the front carb, the one that is fine, with the carb upright, I meet no resistance. But the back carb, the one that is acting up, it hard to blow through. Perhaps there is some buildup there? However, if that is so, then that would likely restrict fuel flow rather than make the valve stay open, no?
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