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Fuel leaking on to intake manifold...?

16K views 14 replies 10 participants last post by  302 Z28 
#1 ·
Probably a silly question and I'm pretty sure of the answer, just wanted expert confirmation.

Pictured below on the intake manifold is a dried on yellow deposit which I believe would be fuel which has leaked from the carburetor?



If this is so, does anyone know what the most likely culprit is causing this issue? Would it be the separating gasket between carburetor and manifold?

Thanks :)
 
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#2 ·
That is fuel and its coming from the carb probably the line or the pump pr shafts seals. Either way its time for a rebuild. How long has it been on the car it looks pretty clean. May just need some love or maybe even to be driven more if that an issue. But with gas leaking its best to get it sorted before you go to much further.

Is the fuel line fully sealed up any chance its coming from there and dripping down long the carb body. Low likes tend to hide them selves so its best to check the most likely source first. Put a wrench on the fitting and see if its tight should also not be too tight. Those aluminum fittings are not made to be cranked on.
It is pretty new, no more than two years I'd say and less 1000 miles of usage. I've not come across any fuel from the line, there's nothing damp and I've never seen any drips. I will give see if fitting is loose though. Pump shaft seals??
 
#6 ·
In your picture it appears you have a manual choke and it is wired open (inactive). Sometimes locking the choke out will require additional pumping of the gas pedal to keep it running, which can cause excessive fuel from the accelerator pump to leak past the throttle shaft, resulting in stains such as yours.
 
#7 ·
Looking at your picture of the carburetor I do not see any stains on the secondary housing or on the carburetor's main body. I would start by checking the fuel line maybe uninstalling it and then reinstall it. The stain is mainly on the baseplate. Check the carburetor base gasket, when you have the carburetor use a straightedge to check the baseplate to see if warped. Use two base gaskets when reinstalling the carburetor. Also check around the secondary throttle blade shaft.
 
#8 ·
Another thing you can check too is quite easy and has happened to me before since I don't drive my trucks all the time as I installed some brand new or rebuilt carb's on or just new gaskets they have no leaks at first but after several heat cycles the fuel bowls sometimes just need to be retightened a hair to seal it back up and no leaks.

99 times out of 100 its always the rear more so then the front and I have had the same with center hung and side hung fuel bowls. I always spray my fuel bowl gaskets with wd40 or use chapstick on them so they are easier to come off and even though they say non stick that can get on there pretty good sometimes that they do tare when taking them off. Be careful and don't over tighten them as it won't take much to strip the fuel bowl screws. I use a nut driver and turn them very slowly a few turn at a time on each one in a criss cross pattern and then once they are not able to turn loosely any more I turn it some more but with a light grip and once my hand will still turn around the handle and the nut driver itself no longer tightens then I know its enough.

It does not take much to strip them threads out and over tighten. Be careful with the base plate too as only about 6 ftlbs of torque is all that is needed. Also if the carb would happen to overflow and flood with the needle and seat sticking then the fuel comes out of the vent tube or the boosters and dribbles down the carb and sometimes some will seep through the throttle shaft but it does not mean the throttle shaft is bad.
 
#9 ·
I can tell you just from the picture that the dual feed fuel line you have is not the correct one for your carb. It is for a dual feed carb that has a metering block on the rear just like there is on the front, which makes the carb longer and the fuel inlets farther apart. The line you have has been mangled to shorten it up. That may be the source of the leak. Line that is there is for a 4150, you need one for a 4160.

Also check the gaskets on the float height adjuster screws, make sure things are tight there, and check bowl retention screws to make sure that are tight.

High float height and too high fuel pressure have already been suggested.
 
#10 ·
Probably a silly question and I'm pretty sure of the answer, just wanted expert confirmation.

Pictured below on the intake manifold is a dried on yellow deposit which I believe would be fuel which has leaked from the carburetor?



If this is so, does anyone know what the most likely culprit is causing this issue? Would it be the separating gasket between carburetor and manifold?

Thanks :)

This could use better isolation between the carb and intake. A simple gasket allows too much heat transfer between hot intake and carb. At least a 1/2 inch phenolic spacer also a Holley heat shield is nice to deflect heat away from the bowls. These things keep the fuel in the bowls from boiling away after shut down. A lot of the fuel ends up in the throttle bore of the secondary which then runs out the throttle shaft ends. Another trick is to use a length of fuel hose to connect the front and rear bowl vents. The hose would have a hole carved into the top of the apex to provide the vent. The height and length of the hose helps keep the venting fuel from escaping into the throttle bores.


Also, be careful when torqueing the hold down bolts on the Holley it is easy to bend the mounting arms which results in a vacuum and fuel leak where the throttle bore plate meets the manifold.


Bogie
 
#11 ·
Probably a silly question and I'm pretty sure of the answer, just wanted expert confirmation.

Pictured below on the intake manifold is a dried on yellow deposit which I believe would be fuel which has leaked from the carburetor?



If this is so, does anyone know what the most likely culprit is causing this issue? Would it be the separating gasket between carburetor and manifold?

Thanks :)
If you look closely at the manifold directly under the fuel inlet you can see a spot where the stain looks washed. I would inspect that fuel inlet line very closely because it is dripping on the manifold when the air in the engine compartment is still. If the air was moving then the drip would not go straight down like that.
I am surprised that nobody else spotted it.
 
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