Rochester 4GC gushing fuel from secondary vent tubes.
October 8th, 2012, 12:47 PM
#1
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Posts: 99
Rochester 4GC gushing fuel from secondary vent tubes.
The Rochester 4GC carburetor on my Olds 215 engine has begun to push fuel
up through the secondary vent tubes on the air horn at startup. Engine will
start and run approx.10 seconds before fuel begins to flow from the vent
tubes and floods the engine,stalling it.Trying to restart it is futile.After 5
seconds of cranking,fuel once again begins to POUR from the tubes into
the engine.
Removed carb and checked float levels and drops to factory specs in
repair manual.Reassembled carb and tried again.Same thing.This happened
after two tear-downs and rechecks of floats.
Carb was rebuilt using repair kit from Fusick,with flat neoprene needle and
seat assemblies. The engine ran fine for the entire summer with this setup,
until this problem suddenly began. Do these neoprene needles and seats
have issues like this? Is this a float adjustment problem? I no longer have
the spec sheet that came with the rebuild kit,I'm setting the floats to the
specs in the factory repair manual
up through the secondary vent tubes on the air horn at startup. Engine will
start and run approx.10 seconds before fuel begins to flow from the vent
tubes and floods the engine,stalling it.Trying to restart it is futile.After 5
seconds of cranking,fuel once again begins to POUR from the tubes into
the engine.
Removed carb and checked float levels and drops to factory specs in
repair manual.Reassembled carb and tried again.Same thing.This happened
after two tear-downs and rechecks of floats.
Carb was rebuilt using repair kit from Fusick,with flat neoprene needle and
seat assemblies. The engine ran fine for the entire summer with this setup,
until this problem suddenly began. Do these neoprene needles and seats
have issues like this? Is this a float adjustment problem? I no longer have
the spec sheet that came with the rebuild kit,I'm setting the floats to the
specs in the factory repair manual
October 8th, 2012, 01:00 PM
#2
Registered User
Join Date: Jan 2007
Location: Texas
Posts: 218
I have seen a similar problem on Q-jets when the mechanical fuel pump starts going bad and the pressure is over riding the float and inlet needle/seat ability to close off the fuel flow. Try a diff. fuel pump?
Just my thoughts
Danny
Just my thoughts
Danny
October 8th, 2012, 03:15 PM
#3
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Thread Starter
Join Date: Nov 2010
Posts: 99
The fuel pump can produce TOO MUCH pressure? Always beleived that
a fuel pump failed because it couldn't produce ENOUGH pressure. What
happens inside a fuel pump that would cause it to do that? Your answer
does make sense because I've torn down the carb three times to check
floats and float levels,the last time to change the needle/seats back to
the original pointed set. The rebuild kit set had FLAT neoprene needles
& seats. With the old needle/seats in it,fuel still poured from the vents
after approx. 10 seconds of cranking the engine. I will give your theory
a try. Thanks
a fuel pump failed because it couldn't produce ENOUGH pressure. What
happens inside a fuel pump that would cause it to do that? Your answer
does make sense because I've torn down the carb three times to check
floats and float levels,the last time to change the needle/seats back to
the original pointed set. The rebuild kit set had FLAT neoprene needles
& seats. With the old needle/seats in it,fuel still poured from the vents
after approx. 10 seconds of cranking the engine. I will give your theory
a try. Thanks
October 9th, 2012, 03:45 PM
#5
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Join Date: Nov 2010
Posts: 99
I switched the upper part of the Rochester 4GC (air horn) with another
Rochester 4GC I had as a spare.Float settings were the same.
Started the engine and there was NO fuel flooding from the vent tubes.
Ran engine for about 10 minutes. Noticed fuel seeping from gasket near
fuel inlet. Engine was running rich,but don't know if it was because of the
carb or the amount of gasoline that may have been lying in the manifold.
Ordered new fuel pump to try 70Wcars theory.Still think that the pump
may be pushing too much fuel.
Would the placement of the fuel filter have anything to do with high
pressure? Mine is placed before the fuel pump.Would it be better to place
it between the pump and the carb?
Rochester 4GC I had as a spare.Float settings were the same.
Started the engine and there was NO fuel flooding from the vent tubes.
Ran engine for about 10 minutes. Noticed fuel seeping from gasket near
fuel inlet. Engine was running rich,but don't know if it was because of the
carb or the amount of gasoline that may have been lying in the manifold.
Ordered new fuel pump to try 70Wcars theory.Still think that the pump
may be pushing too much fuel.
Would the placement of the fuel filter have anything to do with high
pressure? Mine is placed before the fuel pump.Would it be better to place
it between the pump and the carb?
October 10th, 2012, 10:57 AM
#7
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Join Date: Nov 2006
Location: SE Wisconsin
Posts: 1,917
If it is an in-line fuel filter, I have only seen them installed between the fuel pump and carb, not between the gas tank and fuel pump.
How long has your fuel filter been in the current location? If forever, then it is not likely the source of your problem.
How long has your fuel filter been in the current location? If forever, then it is not likely the source of your problem.
October 10th, 2012, 11:16 AM
#8
"me somebody" site member
Join Date: Jul 2007
Posts: 1,612
That's what I would have guessed. Since replacing the air horn solved the first problem, but now you have another, maybe you should go back to the old horn and see if you can figure out why the float was (apaprently) hanging up in it (you could hold it right side up, with the floats hanging, and push them up and see if they drop back down).
Of course, on the 4GC, the fuel filter is typically the stone variety, located IN the fuel inlet housing.
Of course, on the 4GC, the fuel filter is typically the stone variety, located IN the fuel inlet housing.
Last edited by aliensatemybuick; October 10th, 2012 at 11:20 AM.
October 10th, 2012, 11:29 AM
#9
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Thread Starter
Join Date: Nov 2010
Posts: 99
Took the Cutlass out for a hard test drive this morning.Ran well with no
fuel leakage. Problem must have been float related,as the gushing problem
went away with the air horn and float swap.
Fuel filter has always been placed before the fuel pump,but will be changing
it to between the carb and pump.
Fuel leakage at the front of the carb was due the inlet fitting was not tight
enough,and had to give the screws on top of the air horn some extra twist
too. There is no stone filter in it. Can't seem to find one anywhere.
So far all is well and will be checking the problem air horn assembly to
see what the malfunction is.
fuel leakage. Problem must have been float related,as the gushing problem
went away with the air horn and float swap.
Fuel filter has always been placed before the fuel pump,but will be changing
it to between the carb and pump.
Fuel leakage at the front of the carb was due the inlet fitting was not tight
enough,and had to give the screws on top of the air horn some extra twist
too. There is no stone filter in it. Can't seem to find one anywhere.
So far all is well and will be checking the problem air horn assembly to
see what the malfunction is.
October 14th, 2012, 08:05 AM
#11
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Thread Starter
Join Date: Nov 2010
Posts: 99
Tested the fuel pump pressure and it is at a little over 5 pounds.Holds good
at that level for over 60 seconds.Rules out the fuel pump as a cause of
the flooding problem I was having. Conclusion is that a stuck float in
the secondary side was the cause of the fuel overflow.
at that level for over 60 seconds.Rules out the fuel pump as a cause of
the flooding problem I was having. Conclusion is that a stuck float in
the secondary side was the cause of the fuel overflow.
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