[mgoblue]

I've had my '69 350 2bbl THM for a long time, but I've never had this problem until this summer. I go for a 30-minute drive, and it runs great. The next day I go to start the car (without giving it any gas) and it starts very rough and stalls. I assume it is flooded but there is no evidence of that at the carb. I pull the spark plugs and every one of them has a light coat of fuel on the electrode. It is definitely fuel, not oil. So, I clean and reinstall them. The car then starts right up and runs great. The next day it's the same problem - car starts very rough and stalls. Again, fuel on all of the spark plugs. What could be causing fuel to get on the spark plugs overnight while the car is just sitting in the garage?

[Gach]

Most likely the carburetor, what kind of carb you running.

[steve25]

Two things can be happening here and both are related to todays fuel which boils and turns to a vapor at a much lower temperature then straight gas that’s not cut with Alky.

First off you need to make sure all the screws that hold on the carbs top lid are tight, but more importantly the screws that hold on the pump cluster above the throttle bores need to be tight and the only way to tighten them on a 2 bbl is to remove that air horn lid, and this all means you will need a rebuilding kit to do this all.

2) the float level needs to be set a little low for today’s fuel .
The float specs used originally and given as spec’s in the rebuilding kits will many times not work for todays fuel.

3) when you turn off the motor when it’s fully heated up from a drive not only will the todays fuel vaporize in the bowl, but it will do so also in the fuel line leading from the pump to the carb.
This added pressure can open up the fuel inlet needle in the carb and the end result is wet plugs .

4) also the rubber sealing tip on the nose of your needle may be getting eaten up by todays fuel and you even now maybe running running right on the edge of having the carb flood out on you as it does once you shut it down hot.

In short your plan should be to rebuild the carb , and during that process lower the float level by 1/16” and get some fuel line insulation around the line that runs from the pump to the carb .

I don’t know that anyone makes a off the shelf insulating carb mounting gasket for a 2 bbl, but you make one out of a thin type carb gasket and a thin 1/4” thick slice of wood which is what I have seen the dirt track racers do on there 2 bbl carbs.

[Schurkey]

If the engine STALLS, (or diesels) you've got unburned fuel rolling around in the intake manifold.

If the engine shuts off normally, and you have spark-plug fuel fouling, look at the carb and fuel pressure.

[Cliff R]

Choke sticking closed or not "unloading" far enough on a cold start?

I'd start there first as that will cause all the symptoms that you are seeing on a cold start, running rough, poor idle quality, fouling out the spark plugs, etc....

[Aaron65]

When I was a kid, my lawn mower would slowly gas foul the plug. I'd take it out and clean it, and the mower would run fine for a while. After a few weeks of that, I changed the plug and everything was fine. Is there anything in your ignition system that could be getting worn out (points, condenser, etc.)? Never rule out ignition with "fuel" problems.

[steve25]

Simply put, if once the car is up to normal temp ( as in driven for 10 to 15 minutes) if it can then idle fine for 5 minutes with the car in gear then the issue has nothing at all to do with spark, but it all lies with the carb

[Formulajones]

I've run across that in the past and it's usually one of 2 things.

Something on the carb is leaking internally after shutdown. Not uncommon when heat soak sets in.
A leaky well plug or needle and seat or gasket etc... Usually a full and proper carb rebuild fixes that issue.

The other thing I've seen more often is a fuel tank that isn't venting properly. They build pressure from heat this time of year and after shutdown Ive seen that excess pressure push fuel past the needle and seat and drip fuel off the boosters, flooding the engine.

It's pretty easy to chase down. After a nice drive, shut the car down, pull the air cleaner and watch the boosters. Any nozzle drip is a sign of something pushing fuel past the needle. From there you just have to figure out why.

An internal carb leak like a gasket or plug is a little more difficult to see as it could be leaking somewhere below the booster that isn't visible.

[geeteeohguy]

What Steve25 said, 100%. BTDT many, many times with many cars, and that is the issue. Today's fuel.

[mgoblue]

Originally Posted by Gach

Most likely the carburetor, what kind of carb you running.

Original Rochester 2GV

[Gach]

Originally Posted by mgoblue

Original Rochester 2GV

First thing I’d check is the needle and seat. Under pressure driving it may be seating, but once it sets. Might be leaking fuel making the plugs wet. One indication is when you start it, at times may need a couple of pumps. Not always may depend on how long it sets between start ups.