Q-jet fuel feed questions
April 8th, 2012, 01:03 PM
#1
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Q-jet fuel feed questions
So I recently had to replace my 71's carb after the float on the original one somehow got stuck open and flooded the engine. I had rebuilt a 73 Q-jet just in case of a problem like that. When I put the 73 on, I was amazed by how much better / smoother the car was running than with the original.
I have one of those see through filters in line between the pump and the carb and I noticed that the filter stays full for days at a time with the new carb. It always "bubbled away" after a few seconds with the old carb.
Anyway, what would cause the fuel to run back through the pump towards the tank (don't say "gravity"
)? Would that be a leak in the carb or maybe in the carb mounting gasket? Could that be a problem with the mechanical fuel pump?
Also, can the fuel pump get hot enough to boil the gas? That could also be causing the bubbling in the see through filter... I guess?
I have one of those see through filters in line between the pump and the carb and I noticed that the filter stays full for days at a time with the new carb. It always "bubbled away" after a few seconds with the old carb.
Anyway, what would cause the fuel to run back through the pump towards the tank (don't say "gravity"
)? Would that be a leak in the carb or maybe in the carb mounting gasket? Could that be a problem with the mechanical fuel pump?Also, can the fuel pump get hot enough to boil the gas? That could also be causing the bubbling in the see through filter... I guess?
April 16th, 2012, 02:23 PM
#2
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Posts: 333
Do you by any chance also have the standard paper filter in the carb inlet, and if so does it have the spring-loaded valve in it? Supposedly this little valve keeps fuel in the carb, although it might restrict high-volume flow unless you clip a couple coils off the spring...
The only reason I mention it is because I've noticed the opposite problem after changing carbs; now it drains, whereas before it did not. And I did have a valve in the old (short) filter, and no valve in the new (long) filter.
The only reason I mention it is because I've noticed the opposite problem after changing carbs; now it drains, whereas before it did not. And I did have a valve in the old (short) filter, and no valve in the new (long) filter.
April 17th, 2012, 10:10 AM
#3
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Join Date: Mar 2011
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Hmm.. I have the long filter, with rubber o-ring and check valve in there. It is brand new in the new carb as I just rebuilt this carb. But, I think I've tracked my problem down (or at least one of them).
The fuel does still bubble away after all. BUT, it shows up again after everything cools off and refills the see-thru filter.
So what I am thinking is that the fuel is boiling/evaporating in my mechanical fuel pump. I can hear a noise in there and using a screw driver as a hillbilly stethoscope, I think it is actually boiling after the car is shut off.
If anyone has any suggestions why that might be happening, I am open to ideas...
The fuel does still bubble away after all. BUT, it shows up again after everything cools off and refills the see-thru filter.
So what I am thinking is that the fuel is boiling/evaporating in my mechanical fuel pump. I can hear a noise in there and using a screw driver as a hillbilly stethoscope, I think it is actually boiling after the car is shut off.
If anyone has any suggestions why that might be happening, I am open to ideas...
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