Reply To: Carburetor percolation

[Jim Chase]

Paul, A photo would be great, thanks. Based on your comments I suspect I have the direction of the outlet line on top of the fuel pump wrong, it should be coming outboard towards the hood rather than forward. In retrospect it was pretty dumb wondering why the line took the kick up towards the manifold, it should have been turned 90 degrees.

Greg, getting the fuel line over to run fwd along the hood ventilation doors should be ideal. The air coming out of the radiator should roll across the fuel line on its way out when the doors are open. That air is about 140 to 150 degrees, which is actually cooling when the fuel evaporation problem is generally happening with the fuel being heated in the range of 150 to 180. The exhaust manifold goes way over 600 degrees and is probably heating the fuel pump and line via direct radiation more than convection. The fuel line probably shouldn’t be insulated along that run forward as you are trying to use the 140 degree air to cool the fuel line, whereas insulation will block the cooling effect and absorb more radiation heat from the hot manifold. The insulation will absorb more radiation than the copper line.

I would avoid having the fuel line running back to the firewall. The cooling air coming out the radiator is mainly going to flow aft and down over the engine and manifolds then under the car as well as out the hood ventilation doors leaving a zone of air next to the upper firewall trapped by the hood being heated by the 200+ degree engine surfaces and much hotter exhaust manifold. That air is going to be pretty dead at low speed and idle, and perhaps turbulent but with no definite flow path out at cruising speed, meaning it will be hotter than the air in the forward engine compartment.

Jim