I just installed a rebuilt 300 i6 in my 1966 f100 and it is turning the exhaust red in about 60 seconds at idle. What in the world could be the cause???? It has a rebuilt Fomoco carb and new ignition. I don't get it.

 

Is your heat riser working?

 

What is a heat riser?

 

On a 300 6 cylinder there is a plate between the intake and exhaust.
There is a spring above and to the left of your exhaust pipe directly below your carburetor.
This plate closes to heat the carburetor and heat expands and opens the heat riser.

 

Heat riser from above heat diverted away from carburetor.


Heat riser from above Heat diverted too carburetor.



Heat riser cold engine position.


You should be able to move heat riser counterweight back and forth.
It may be stuck.

 

Sounds to me like the engine is running way too rich and/or the ignition timing isn't adjusted correctly.

 

x2

A heat riser that's stuck is just going to cause drivability issues.

 

It's the opposite, too LEAN and the exhaust will glow red hot. Also the timing, too far retarded can cause this especially at higher rpm without a load, such as when breaking in a new cam. New engine, did you hook up the vacuum advance?