Vapor Lock

[jstillmd]

Hey Everyone,

I've noticed a few times after trying to start the car after CC that it hesitates to start and I think it's vapor lock. Happens especially if I drive the car and stop and try to start it again after 20 min or so aka it hasn't had time to cool down yet. It's a 427R running on 91 octane. Thanks! See some of you in a few weeks at CC...out of town the next two weekends.

Jon

[bobcowan]

If it spins over easily but won't fire, it's probably vapor lock. If it hesitates to spin over, it's probably an electrical problem - like too small a battery cable.

[Gaz64]

What carb/s do you have?

Sounds more like fuel percolation.

[Tommy]

We need a little more info to diagnose. Are you running a mechanical or electrical fuel pump?

[xb-60]

Does it help if you turn it over without touching the throttle, and when you hear it just start to catch slightly (might be 10 seconds of cranking), just give it a touch on the accelerator pedal?
Cheers,
Glen

[jstillmd]

It's a Holley 750 with mechanical secondaries. I'm not sure about the fuel pump. It's a Superformance Mkiii built in 2006. I'd have to look at the build sheet to find out. In these situations, if I floor the throttle it'll start but blow smoke out the exhaust. Usually isn't a problem unless the car is hot.

[BAsque1]

Originally Posted by jstillmd

Hey Everyone,

I've noticed a few times after trying to start the car after CC that it hesitates to start and I think it's vapor lock. Happens especially if I drive the car and stop and try to start it again after 20 min or so aka it hasn't had time to cool down yet. It's a 427R running on 91 octane. Thanks! See some of you in a few weeks at CC...out of town the next two weekends.

Jon

Welcome to my world. As the other responders are saying there is a plethora of thing that can be affecting this. I have a 427 FE Side Oiler with the same problems and this is what I have done in no particular order.Checked the block, heads, header , exit hose and intake manifold temp after 1hr run with an INfra red thermometer for overheating.

Check your coolant water mix should be 50/50 water/coolant plus 1 bottle of water wetter.

changed the starter for a hi-torque starter and covered with a heat shield.
installed a phenolic 1/2" spacer between the carb and the manifold to reduce heat transfer.

Checked the gas level in the carb bowls to ensure is specs.make sure that you are not dripping gas into the plenum vua looking down the carb after a run.

checked timing.

heat shielded the gas line from gas pump(mechanical) to carb and incoming hose from tank to gas pump immediately underneath the headers)

Changed the gas filter element.

Theoretically the heat from the engine is overboiling the gas leaving us with slim to no gas on the carbs making it difficult to start or maintain nice idle in heavy traffic. That is vapor lock. I thought about installinf a cool can, however, space availability and net positive effect did not warrant the expense. Plus you would have to carry a cooler with dry ice in the trunk, not too convenient.

I sincerely hope that one of these things work, the starter option I knew I had to change the starter for I rather have the hi-torque type thats just me.
Happy motoring.
Basque1

[mr0077]

That's a slightly rich or flooded condition from heat percolation, not vapor lock...just hold the pedal to the floor during hot starts. Aggravating but managable.

[snakebittexan]

Big believer in a phenolic spacer for these issues--with our government corn gas it's going to become a necessity. A serendipitious effect is improved midrange performance.

[jstillmd]

Yeah if I hold the pedal to the floor during hot starts it will usually start...it sounds ugly and I just want to make sure I'm not hurting the engine. So this is ok to do?

I've also read about phenolic spacers. A lot of people seem to like them so I'm going to consider that as well.

Thanks for all the suggestions!

[Curt C.]

Hard to avoid percolation in Las Vegas. Phenolic spacers, heat shiedling of fuel lines help to a degree but it is hard to completely avoid it in summer time. Pedal on the floor while starting usually gets it fired

[eddyjuan554]

Poulan Pro 18.5 horse mower. two years old. Gets hot and shuts down. All filters replaced, new plug and oil change. Had $300 worth of work done and still not running right. I was told it could be vapor lock.

[vatdevil]

Using ethanol free gas or blending in race fuel helps.....higher vapor point.

[Tommy]

Originally Posted by eddyjuan554

Poulan Pro 18.5 horse mower. two years old. Gets hot and shuts down. All filters replaced, new plug and oil change. Had $300 worth of work done and still not running right. I was told it could be vapor lock.

Apparently, that damn Shelby would put his name on anything if the price was right.

[Sailfish]

I experienced the same sort of situation with my Superformance. I experimented with different "fixes" but the most helpful was installing a wooden spacer under the carb. I tried a phenolic 3/4" spacer and it helped, but at the urging of a friend, I switched to a 3/4" wooden spacer and that all but cured it. I don't have a supplier name, or source, for the wooden spacer-----a friend had it and gave it to me. It appears to be a laminated wood, similar to high-grade marine plywood. It is definitely not a home built product.

[vector1]

Originally Posted by eddyjuan554

Poulan Pro 18.5 horse mower. two years old. Gets hot and shuts down. All filters replaced, new plug and oil change. Had $300 worth of work done and still not running right. I was told it could be vapor lock.

did they check your valve clearance?

[Rick Parker]

eddyjuan554

Get some goats........no gas and they will keep it short.

[rpatton3]

45-50 years ago, drag racers in Arkansas used wooden clothes pins to work a heat sinks and to keep gas line away from heat sources.

They also iced down intake manifold to prevent vapor lock. Who knows if it worked?

[ERA 778]

Clothes pins! Yeah, I remember! One time I must have put 20 of them on the fuel line going to a Carter AFB 4-barrel that was driving me crazy because it wouldn't start when hot! Boy, haven't thought of that in years. You should have see it - clothes pins clamped along the entire length of the fuel line. Can't remember if it fixed the problem or not...

[WardL]

If you can wait until June you can get some summer gasoline which is less likely to cause vapor lock. I expect your problem is more likely due to ethanol than vapor lock. Does the manufacturer say anything about using gasoline with ethanol?