Vapor lock

enjenjo · September 04, 2005, 06:11:06 PM

As you may remember I had trouble with vapor lock this spring on my trip out west, with both vehicles I drove. Now Ken's Caddy is having similar problems. I am told that reformulated gasoline is more prone to this on carbureted cars. Anyone with experience curing it? I need some ideas.

tom36 · September 04, 2005, 06:43:56 PM

Quote from: "enjenjo"As you may remember I had trouble with vapor lock this spring on my trip out west, with both vehicles I drove. Now Ken's Caddy is having similar problems. I am told that reformulated gasoline is more prone to this on carbureted cars. Anyone with experience curing it? I need some ideas.

I've used phnolic (sp?) spacers between the carb (s) and manifold to prevent heat transfer to the carb. I could actually hear the gas boiling in the carbs on a flathead. Years ago, an electric fuel pump used to work on a flathead. Tom..

GPster · September 04, 2005, 07:20:28 PM

I read at one time that one of the reasons for vapor lock is the size of fuel lines compared to the efficiency of the later model fuel pumps. When you have too small a fuel line plus a fuel pump that is capable of delivering 8# of pressure rather than 4# or 5# it is actually letting the fuel flash in the fuel line because the pressure is below the new fuel vaporization point because the fuel pump is actually pulling a vacuum on the line from the tank. CURES WOULD EITHER BE A LARGER FUEL LINE OR AN ELECTRIC FUEL PUMP AT THE TANK TO PUSH THE FUEL TO THE ENGINE (sorry, I hit caps lock and I'm not going to erase it and re-type). Gas with lead in it is heavier. GPster

Crosley.In.AZ · September 04, 2005, 07:37:59 PM

yep the custom blend gasolines will vapor lock easier

need to isolate if the problem is the carb or the fuel pump & line heating the fuel.

I built a little aluminum shield , used the front bolt of the ful pump on a sbc to attach it on a 1974 GMC truck. Helped a great deal.

My 71 chevy truck I ended up runing a return/bypass line to the tank. I changed the fuel pump to the 3 port style. Never had a lick of trouble from it again.

Dave · September 04, 2005, 07:39:23 PM

(sorry, I hit caps lock and I'm not going to erase it and re-type). GPster[/quote]
Thats a bad additude if i ever seen one.

Dave

enjenjo · September 04, 2005, 07:46:38 PM

Well we are insulating the fuel lines, using header wrap for a start to see if it helps. Also going to a insulated spacer under the carb. It already has a 3/8" fuel ine, 5/16" return, and an electric pump back by the tank. Right now it has 3.5 psi fuel pressure, may up that and see if it helps. May jet just a tad richer too. keep 'em coming.

Crosley.In.AZ · September 04, 2005, 08:06:09 PM

Quote from: "enjenjo"Well we are insulating the fuel lines, using header wrap for a start to see if it helps. Also going to a insulated spacer under the carb. It already has a 3/8" fuel ine, 5/16" return, and an electric pump back by the tank. Right now it has 3.5 psi fuel pressure, may up that and see if it helps. May jet just a tad richer too. keep 'em coming.

is it possible there is a venting problem at the tank?

GPster · September 04, 2005, 08:28:00 PM

Quote from: "N8DC"Thats a bad additude if i ever seen one.
Dave

I'm using a computer that might let me do something at CHAT tonight rather than just listen. I'm trying to save wear-and-tear on my finger. The other one is busy right now saluting you. GPster

PeterR · September 05, 2005, 04:53:44 AM

A friend had a vehicle which suffered from vapour lock every hot day. All the normal cures were tried unsuccessfully.

As a last resort I installed a T hose fitting in the fuel line right at the carb inlet and a tank return line from the T. The return leg of the T had a slug of brass soldered in then a 1/16" drill run through. The small hole allowed vapour to pass through easily but provided adequate restriction to liquid fuel to prevent starvation under heavy load.

This worked better than I had ever hoped and the vehicle has never experienced a problem since. Vapour is dispelled from the highest point, and the trickle of fuel running through the system helps to keep the pipes cooler.

enjenjo · September 05, 2005, 11:21:23 AM

Quote from: "PeterR"A friend had a vehicle which suffered from vapour lock every hot day. All the normal cures were tried unsuccessfully.

As a last resort I installed a T hose fitting in the fuel line right at the carb inlet and a tank return line from the T. The return leg of the T had a slug of brass soldered in then a 1/16" drill run through. The small hole allowed vapour to pass through easily but provided adequate restriction to liquid fuel to prevent starvation under heavy load.

This worked better than I had ever hoped and the vehicle has never experienced a problem since. Vapour is dispelled from the highest point, and the trickle of fuel running through the system helps to keep the pipes cooler.

The Caddy has a similar system on it, but it has a 3 1/2 psi check vakve instad of an orfice. I may change that.

1FATGMC · September 05, 2005, 11:41:01 AM

Quote from: "tom36I've used phnolic (sp?) spacers between the carb (s) and manifold to prevent heat transfer to the carb. [/quote

I had some of these problems with the Q-Jet years ago (forgot all about it) and put in one of the spacers with multiple sheets of different material, maybe a Mr. Gasket, and have never had the problem again.

c ya, Sum

purplepickup · September 05, 2005, 12:05:53 PM

Because my hood sides are open and louvers on the hood I get good air circulation and hadn't had a problem until one day cruising on Woodward Ave in dead stopped traffic on a near 90 degree day. The truck stalled and wouldn't start. After sitting a while it started fine. I assumed it was vapor lock. When I got home I installed a 1" phenolic spacer and haven't had any problems since.

It might be all in my head but an added benefit is a little snappier throttle response. :0-0