Q-Jet well plugs

[DeVillain]

Good afternoon/evening/morning gentlemen. So I'm in the process of repairing my well plugs in one of my qjets( M4ME) Just want to get different points of view on this relatively simple repair. Im all ears.

["Cadillac Kid" Greg Surfas 15364]

JB weld by all means
Greg Surfas

[79 Eldorado]

I did mine with a 2 part epoxy years ago. Probably a predecessor to JB but it looked similar. Clean and rough the surface. Be careful that you don't go so crazy with the epoxy that that area no longer fits in the pocket into which they protrude. Through away the sponge they give you in the repair kit.

Interesting thing too I didn't see any signs mine were even leaking but the Rochester book I was reading strongly suggested taking care of it.

Scott

[klinebau]

The very early Quadrajets (before 1969) are prone to leaking from the well plugs, but it is rare to occur in later units  What many perceive to be a leak is actually evaporation of the fuel from the bowl as today's fuel is much more volatile.  Internet myths will persist, however.

That said, I re-seal all of the carburetors that I rebuild to eliminate that as a potential issue.  JB Weld will eventually soften up with prolonged exposure to the new fuel.  The correct way to seal the plugs is to drill them out, tap, and then insert a threaded rod sealed with marine tex.

[Scot Minesinger]

Scott,

What you wrote about fuel evaporation is why I do not remove my 1970 carbs and make the plug repair.  Might not entirely solve the problem.  Plus, it takes 72 hours for my Cadillac to take a few more seconds to crank, and that would be one very very slow leak.  The evaporation theory makes more sense.  Any way to test this?  Maybe put plastic wrap around carb and see if that prolongs the good starting?

[fishnjim]

Scott, this has been studied.  No need to test.  Was an article in the self started too.  These reports might be a bit over the average reader, but look at the graphs and charts/conclusions.   
The issue is ethanol makes some of the "other" gasoline components "more volatile" due to co-evaporation/distillation.   I have done a bit of checking into this after hearing so many stories.   I'm a Chem E - retired.   The period fuels were even different than today's base non- E stocks, more "heavies".
Reports below. 
A carb can be envisioned as a small vented pot(float chamber) of gas, sitting on a hot engine after it shuts off.   So for a time, it's slowly boils off the low boilers with no feed from the mech. fuel pump.   This doesn't/can't occur in a FI system that's closed and under high pressure and these "E" fuels were formulated for FI.

[TJ Hopland]

If you are going to seal them check the label to make sure gasoline is listed as ok on the package.   JB weld for example comes in several, possibly dozens? of flavors now and some do better than others in the environment we are talking about here.

If you want to test the heat soak evaporation theory try opening the hood when you park and leave it open till it cools.  Not having the hood there to trap the heat will make a huge difference on how high the temps get and how long they stay high.

Until I went EFI on my 73 I had an aftermarket electric fan in front of the radiator hooked to a simple mechanical wind up timer inside the car.   Anytime I would shut it off I would just wind the timer up to about 10 mins.  Just that little bit of airflow was enough to keep the fuel from boiling out.  It doesn't take much because in this case the flow was hot air coming from the radiator.   This car was so bad that on a warm day using E10 you could hear it boiling.

Talking about the 70's cars I wonder if an Eldo was worse than a RWD car because the engine sat higher.  On an Eldo the air cleaner is almost touching the hood insulation.  RWD cars sat a few inches lower.   I wonder how much different the temps are in those few inches?

[Jon S]

 What year is the car in question from the original poster?  I have a Q-Jet on my 1981 Corvette  and have never had any fuel leakage problems.  Also I had a few ounces of Marvel Mystery Oil to the gas and have never experienced evaporation problems even when the car sits for six months at a time.  Yes earlier years had leakage problems. 

[savemy67]

Hello DeVillain,

As you can read, different people have had different experiences with their QuadraJets.  Of the millions of QuadraJets manufactured, I am sure some of them have leaking well plugs, and some don't.  I have also observed that some epoxy products used to repair the leaking well plugs fail over time, and some do not.

As klinebau suggested, the best repair is to drill and tap the plug holes, and install threaded plugs to which a sealer has been applied.  This is however, much more laborious than than just applying a product to the bottom of the plugs.

Whichever method you use, don't forget that there are five well plugs to consider - two primary, two secondary, and the accelerator pump well plug.  All these locations have fuel that constantly sits above the wells. 

Respectfully submitted,

Christopher Winter

[Dave Shepherd]

I might add that over  the years  I found the slow set JB stood up much better than the fast set JB when sealing the well plugs.

[Lexi]

JB Weld worked great. No sign of softening after 3 or 4 years. Clay/Lexi