Road tour - vapour lock

[Tolle]

Hi guys, I`m going on a US. road trip, have a look at, www.lh2013.com
The organizers  warn about vapour lock , going through some of the hotter desert states. I`ve read a carb spacer will prevent this , will a spacer have any other affect on the engine operation? Engine is a 350 sbc.
Stock 300 Hp. coated headers in a fendered model A roadster with only the hood top on . Should I be worried.
Thanks Tolle.

[wayne petty]

vapor lock is where the fuel lines or the fuel pump get hot enough to boil the fuel into a vapor..

at that point the fuel pump cannot handle the expanding vapor..  so it pushes the fuel before the pump all the way back to the tank...   but there is not enough fuel to keep the engine running... it leans out gets really hot and stalls.. makes it hard to crank also..

the expanding fuel vapors inside the fuel pump are also a huge issue..

restricted fuel filters can lower the pump inlet pressure causing vapor lock easier...

powdered rust in the fuel system will hold the fuel pump check valves open and reduce or stop the fuel pump from working at the worst time..



i have had so many fuel pump fail and when i hooked up a clear vinyl hose to the output and crank the engine to fill it.. it would drain out of the hose and the pump all the way back to the tank...  ya know you are having a bad day when you can blow bubbles in the fuel tank by blowing at the fuel pump outlet..

this also causes cold start.. stall and a bunch of cranking to get it to start again as the fuel pump allows the gas to siphon out the upper level of the fuel bowl so it runs out when you start .. and the pump has not had enough time to pull fuel all the way up from the tank..

a few ways to handle this...


sorry for the length of this reply...

invest in some magnets inside the fuel tank... make sure they get to the bottom.. they will attract any rust to them and keep it out of the fuel system..   and yes i know that nobody has any rust in their fuel system.. but it comes from many sources.. including the gas station pumps..

i normally drop them in and verify they are on the bottom afterwards as i have had a few fall sideways and stick to the inside of the top of the tank.. strong magnets..

i blew out a clogged fuel filter into my clean white drain pan.. and it was full of what looked like rust.. i dropped a tiny super magnet into it..  then i noticed a clean area around the magnet..




i pushed it with my finger..






there are all kinds of neat shaped fuel filters that can be installed inline between the tank and the pump..






or... one can use a standard mid 90s ford fuel filter.



these work with fuel line just by pushing the hose over and clamping them..

there are also versions like this with 10mm inlets





one can find a neat bracket to mount these on a tab of the frame rail on most fuel injected ford trucks. as every parts store will have these in stock for under 10 bucks..

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this is a holley gasket 108-51 similar gaskets should be available in many parts stores.



sediment from the fuel system will also cause what seems to be the fuel to boil over in the carb.. where the sediment holds the needle and seat open slightly allowing any residual fuel pressure held by the pump to overflow the float bowl.. dripping fuel out the throttle shafts..  or flooding the engine..


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getting the engine started after a heat soak where the fuel system has experienced a vapor lock.. pour or spray some water on the fuel pump.. that will condense the vapor and restore pumping ability...

i had one friend who installed a windshield washer bottle and nozzles to spray the fuel pump body when he pushed a button..   i fixed it with magnets...a fuel injection type of fuel filter before the pump and a new fuel pump as i could not get the check valves cleaned with several full flow cranking tests when the line is off the carb and extended into a bottle while somebody cranks the engine with the ignition disconnected to avoid sparks being created..


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open the fuel filter images in a new window to see the part number in the URL if you want one .

[rumrumm]

I ran into a problem a couple of years ago at GG in Des Moines. Temperatures in the mid-90's, asphalt parking areas and streets, low slung car, enclosed hood and very slow stop and go traffic caused my coupe to vapor lock. I had not had a problem previously. Since that happened, I insulated the metal fuel lines from the electric pump to the carburetor and built a heat shield for the pump. That seems to have fixed the problem. I also run a phenolic spacer between the Edelbrock carb and the intake manifold since I heard these carburetors seem to be a little more susceptible to vapor lock than Holleys. Since you don't run hood sides, I don't think I would be too concerned about carburetor getting too hot.  But it might be a good precaution to insulate any metal fuel lines you have. I used vacuum hose and wire ties for this.

[Leon]

I must be lucky because I've lived in the desert for over 40 years and never experienced vapor lock.  We get 120 degrees here and never had it.

[GPster]

Years ago I read an explanation of this problem that was made by an automotive electrician that up-dates restored cars to be driven in todays conditions. In his mind one of the big problem with vapor-lock is too small a fuel line for todays gasoline especially when there will be a high flow demand by a bigger engine. It seems he has found that todays fuels will vaporize at lower pressures and if your engine's fuel pump is pulling more than the line or restriction in the fuel tank will allow the fuel will be under a vacuum in the line and vaporize. This of course be worse if the temperature in places along the line is higher. A fuel pump that is mounted near the tank and is used as a pusher would help this situation. Because you're tanking about a Model "A" I would assume that you have a newer gas line and gas tank than stock so your line size may be sufficient. You might not need to do anything but use good gas. GPster

[Mikej]

Do you use gasohol ? If not I wouild avoid it here. 91+ octane would be advisable. Does your car run cool now? What temp? I see you will be traveling in Iowa 7/11/13. I have a businees, in Logan,  on HWY 30. There is a welcome center between Logan, IA and Missouri Valley, IA. It has a new HWY 30 display. There is also a museum there and gift shop.

[kb426]

My crewcab that pulled the racecar started out with vaporlock. I travel in elevation alot which aggravates the condition. I tried alot of things over about 14 years. As I found improvements, the refineries worked against me. Reid vapor pressure is the measurement term that I remember. The refineries can lower that at will. In turn, the boiling point is lowered. I used a Carter elect. fuel pump mounted as close to the tank as I could get it. It was mounted around the bottom level of the tank so there was always gas in the line from above the pump on startup. My exp. with most pumps are that they have little suction but good pressure pumping. If you don't oversize your pump or install a bypass regulator, you won't aggravate the situation by percolating your fuel.

[enjenjo]

The refineries can lower that at will. In turn, the boiling point is lowered.

They no longer raise the Reid pressure since fuel injected engine run high enough fuel pressure to make it unneccesary.

[Warpspeed]

Fuel has definitely changed since the good old leaded gas days.

I believe todays fuels are now all formulated to work in high pressure EFI systems where fuel boiling at low pressure and high temperature is no longer considered a problem....

There are probably a few things you could possibly do to improve an older carby vehicle.

An electric pusher pump located at the tank would solve many of these vapor lock problems. Another improvement could be made by fitting a return line to the tank fed from a small bleed orifice right at the needle and seat.

That would keep some fuel circulating around the system, and keep the fuel cool wherever it passed close to any hot spots like the exhaust system.

[Arnold]

I must be lucky because I've lived in the desert for over 40 years and never experienced vapor lock.  We get 120 degrees here and never had it.

 Some vehicles got/get vapor lock..and you have to live with it/deal with it.
Other's don't.
I have driven through 120 deg too.No vapor lock either.
BUT I HAVE SEEN THAT DEMON :evil:

 Some vehicles I have owned..dealt with that..figuring it out..
looking back now..