Thread: vapor lock 454

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Hi guys,
I'm hoping someone can advise me how to cure a problem I've had recently. Last weekend I was driving my 68 Iso Grifo (454 BBC engine) home from the Silverstone Classic in the UK. I'd been sitting on about 80mph for about 45 mins on the freeway, when I felt the engine jerk a couple of times. It happened again a couple more times, then the motor cut completely and I pulled over. There was no fuel visible in the glass filter on the fuel line and no pressure at all on the gauge just before the Holley carb. I could hear the fuel pump (Holley 125 electric) was working when I switched on the ignition. When things cooled down a bit, I tried again, fuel gushed back into the carb and she started right up again. When I got home and had been in traffic for a while I looked again under the hood and saw that there was very low fuel pressure and the glass filter was only partly full, so I'm sure the motor would have quit again fairly soon.

I guess this is a vapor lock situation - what should I do? I suppose the fuel line from the tank must run too close to the exhaust somewhere. The pump is back near the tank, so if the problem is between the pump and engine, why doesn't the pump just push more fuel through? I guess the way to go is to lag the whole fuel line with heat insulating sleeving? Any recommendations on products? Should I wrap up the pump in heat shielding too?

Your thoughts would be appreciated!

Thanks,
Chris

ISOs are cool cars....dont see many in the US anymore

If you have an electric pump, it should be mounted as close
to the petrol (see, we can talk Engrish over here) so that the
pump is pushing fuel. Electric pumps are poor at pulling fuel.

How far from the tank outlet to the pump? Since the electric pump
is pushing, the fuel should not vapor lock. However, the line
from the tank to the pump could vapor lock....the pump doesnt
have enough suck to pull out of the condition until all cool down.

Another idea is the pump getting weak OR you are getting a
low voltage condition to the pump that is caused by heat.

mike in tucson

Thanks, Mike.
The pump is brand new and is pretty close to the tank. It is fairly near one of the 3" pipes and its muffler. I will look at lagging everything on the tank side of the pump, and will probably do everything forward to the carb - can't hurt, after all.
Chris

Are you having the same heat wave as europe and russia? Under hood temps maybe higher than normal for you, but moving the fuel lines or insulating may help. Or a regulator and a return to the gas tank to keep the fuel moving.

Just as a test, you could take some insulation (like house insulation)
and wrap it around the fuel line where you think it is exposed to higher
heat. Use some alumninum foil wrapped around the insulation to secure
it....dont compress the insulation too much. That will be a quick experiment
to see if it is heat in a particular spot


another thought...is there a particularly long run of rubber hose in
the system? Rubber hoses should not be longer than perhaps a couple
of feet (British feet is OK). Long runs should be metallic line, never copper.


mike in tucson

Originally Posted by Mikej

...Or a regulator and a return to the gas tank to keep the fuel moving.

^^^this is how I solved this problem with mine... insulating the lines helped to a degree but didn't completely solve it until installing bypass regulator with return to the tank... the cause in my car was poor air circulation in the engine compartment likely due to the absence of inner fender wells but this often happens when fuel line close to exhaust as you described... start with sleeving the line in that area (I use the orange sleeve heat shield material, I don't know what it's called). If you continue to have problems, a bypass regulator will fix it for good.

-Chris

Thanks, guys - this is all incredibly helpful. I've read about fuel return lines. Can anyone describe what the layout is, and what hardware I would need? My pump is a Holley 125 electric (gerotor pump, like some oil pumps and nice and quiet). It is internally regulated at about 7psi.
Thanks,
Chris

You'll need a regulator with a return port on it, then route a 5/16" line from the return port back to your tank, works fine if the return line goes into the top of the tank... Also make sure the line from the regulator to the carb is away and or insulated from high heat sources, too...

Holley pumps run hot if you do not use a return line, and over time they will fail because of it.