1968 Carburetor drains

[franklinair]

A new one on me; After sitting for a few days the carb has lost all fuel. It's an original (4300), o'hauled about 8 years ago. Do I need to do a complete o'haul (kit)?

Neil:undecided

 

[mechanicalguy48]

Its not all that unusual for a carb to percolate its fuel out especially when its hot or the engine has been run hard. The first signs you see of this are usually hot start problems. Additionally the 4300 will leak fuel from near the front air horn. New gaskets will solve the leak. As for percolation, if you have space install a phenolic spacer under the carb to help insulate it from engine heat.(most have this already)

 

[franklinair]

Spacer plate is in place. Engine not hot. After priming the carb it starts right up & runs fine. It hasn't been on the road for the past year, only short runs to move car around. There's fuel stain on the intake, under front of carb.

Neil

 

[gtcs1]

Spacer plate is in place. Engine not hot. After priming the carb it starts right up & runs fine. It hasn't been on the road for the past year, only short runs to move car around. There's fuel stain on the intake, under front of carb.

Neil

Mine had a leak, stain visible on the front too. It was coming from the accelerator pump, leaking.

gtcs1

 

[robert campbell]

The 4300 is a bit like a Rochester Quadrajet. I have a couple laying around. The Qjet was famous for a couple sort plugs on the bottom leaking and draining all the gas from the float bowl. I would be surprised if the aceleration pump would drain the complete float bowl. But a new one on me.

I will take a look.

Rob

 

[franklinair]

I kinda thought that too, Pierre. I guess NAPA might have an accel pump for a 4300 carb.
(I haven't messed with carburetors since the old Strombergs on Chevy 'Blue Flame' sixes, or when my dad let me tinker with the SU carbs on his '57 MGA!)

Neil

 

[gtcs1]

I kinda thought that too, Pierre. I guess NAPA might have an accel pump for a 4300 carb.
(I haven't messed with carburetors since the old Strombergs on Chevy 'Blue Flame' sixes, or when my dad let me tinker with the SU carbs on his '57 MGA!)

Neil

Mine was clearly visible, after a short drive, I removed the air filter bowl, and could see the leak from the accel pump.

Pierre

 

[robert campbell]

Pierre/Neil,
Just went down and looked at two of my 4300 carbs I have. I am very good on Qjets and Holley’s. These are not my specialty.

Visual inspection tells me that the acceleration pump may cause gas film on the top, down the front and on an intake manifold, but it will not drain the float area. If you take the carb off, there are 4 soft plugs “staked” into the carb body. They are at the base of the bowl area above and between the air mixture screws looking from the bottom. Two are connected to passages for the acceleration pump and two are for other purposes to machine holes in the bottom of the float area.

I would suspect that if you are not “percolating” due to heat, then one or more of them must be weeping. These soft plugs are common on the Rochester Qjet and prone to leaking. If they are and it would easy to check by putting a paper towel under the air mixture screws up against the throttle plate in the front. But if it happens over time it may be hard to tell. Like a week to drain out.

You can clean all of the soft plugs with solvent and then apply a mild layer of J/B weld over them. This is what I do on Qjets.

Rob

 

[franklinair]

I've got an o'haul kit coming tomorrow (NAPA). I'll see what's going on when I pull the carb, hopefully this week. (Really busy @ work, engine change on a Cessna 182, annual inspection, and a Cessna 310 -o'haul both props) I'm not complaining though - business has been doing very well despite all the economic palaver.

Neil