Topic: Why boil over for carb in '68 289?

[wunderwerks]

A friend of mine has a '68 289 2bbl. that starts and runs just fine when starting from cold.  It also restarts just fine immediately after shutting off.  Let it set 3 min. or longer and the gas boils out of the carb down the intake and floods the engine making restarting nearly impossible.  He has changed the needle and seat twice, carb kit once and pulled his hair (what's left of it) several times.  The carb has the factory aluminum (approx. 5/8") between it and the intake.  Is it possible the fuel pump pressure regulatory has failed and it's overloading the needle and seat?  What has happened to cause this?

[rocket289k]

Have your friend check the "thermostatic valve" on the snorkel of the stock air cleaner. I had a similar problem with 65 289. The flap within the air cleaner snorkel was stuck open and as a result the hot air from the exhaust manifold kept flowing to the carburetor. The exhaust manifold caused the carb to overheat and the fuel to boil off.  A quick check to determine if this a problem is if the top of the air cleaner is extremely hot the touch. It should be warm but not hot.

Regards,

Ro

[wunderwerks]

Problem may be solved.  After son in law installed a new radiator the car was running extra warm in warm weather which my friend thought was unusual as it had not run warm before in warm weather.  He pulled the thermostat and found a fairly new 192 degree Motorcraft.   He replaced it with a 160 degree and immediately noticed the temperature gauge now indicated a normal operating temp.  Boil over appears eliminated and it now starts when fully warmed.  He also felt that 10% ethanol gas boils at a lower temperature than the non-ethanol and this just added to the problem with the 46 yr. old carburation system.  He is keeping his fingers crossed.