91 octane to stop vapor lock?

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Blackmamba

Blackmamba

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I have a stock 198 Slant six (71 Scamp)
The same story, runs like a dream on the highway, but chokes in the city.

*I've since had an Electric Fuel Pump with return line put in and re-plumbed the fuel line which solved everything :cheers:.
Would filling up with 91+ octane (no ethanol) alone been enough to stop Vapor lock altogether?

Curious to see what you guys think.
 
I would not expect it to change anything. I am not aware that the boiling point of gas or the ethanol added is any different between 87 and 91 octane..... I would be more inclined to find a source of ethanol free gas to see how well that helped.
 
Nope, because it's the fuel temp causing the problem and not the octane rating.
 
It might be you haven't gone far enough, or that FUEL IS NOT the problem


You have a carb base heat isolator? The pump rear mounted? You been careful with line routing away from exhaust?

"What else" does the car have for smog equipment?

My memory fades, "might" have EGR, certainly has (had) carb snorkel heat, and various bullshit devices to screw with timing. Some carbs have temp compensation, and some of THEM are "trouble."
 
67Dart273 said:
It might be you haven't gone far enough, or that FUEL IS NOT the problem


You have a carb base heat isolator? The pump rear mounted? You been careful with line routing away from exhaust?

"What else" does the car have for smog equipment?

My memory fades, "might" have EGR, certainly has (had) carb snorkel heat, and various bullshit devices to screw with timing. Some carbs have temp compensation, and some of THEM are "trouble."
Click to expand...

No heat isolator. Front mounted. View attachment unnamed.jpg
 
Blackmamba said:
No heat isolator. Front mounted. View attachment 1714814264
Click to expand...

Was that your fuel line routing before you added the electric pump?

In that picture your fuel line is resting directly on the heater hoses. And its laying on the valve cover and then routed all the way over to the intake manifold.

That's not right. And a potential safety hazard.

Most vapor lock situations can be solved without an electric pump. Just need a well though out fuel routing with heat isolators and other things to block the heat (shields, heat sleeves)
 
years ago i read an artical about a guy road racing a corvette in the late 50s. was having hot fuel. dont know he had vapor lock. but he put a return line on and picked up some performance. he all so blocked the passage from one float bowl to the other. so after a spin the fuel didnt flood the other bowl.
 
Blackmamba said:
So ethanol in present day gas is not the main cause of gas boiling quicker?
Click to expand...
What does ethanol have to do with the octane rating? You can have the same octane rating without or without ethanol.....were you originally wanting to ask about octane or ethanol ?
 
A front pump is no damn good. You need to consider building a vapor return. Go dance around slant six . org. SOMEWHERE there is an article specifically on slants and fuel problems.

On mine, a 360 then 318, I finally went to EFI. "But before" that the best things I did was to go to a rear mount pump, vapor return system, and a nice carb isolator / spacer. Wix 33040 (5/16) or 33041 (3/8) filters have a 1/4" fitting with a return orifice

WIX-33040.jpg
 
nm9stheham said:
What does ethanol have to do with the octane rating? You can have the same octane rating without or without ethanol.....were you originally wanting to ask about octane or ethanol ?
Click to expand...

In Canada, only 91 and higher octane gas contains no ethanol. So more asking about ethanol and referring to how its not suited for old engines.
 
Blackmamba said:
In Canada, only 91 and higher octane gas contains no ethanol. So more asking about ethanol and referring to how its not suited for old engines.
Click to expand...


It's true that ethanol does evaporate quicker, and that it boils quicker so it could add to the vapor lock problem.
Del posted about a return system and the filter/return.
If you are sure what is happening is vapor lock then that would fix it.

Running an Edelbrock carb are ya?
 
autoxcuda said:
Was that your fuel line routing before you added the electric pump?

In that picture your fuel line is resting directly on the heater hoses. And its laying on the valve cover and then routed all the way over to the intake manifold.

That's not right. And a potential safety hazard.

Most vapor lock situations can be solved without an electric pump. Just need a well though out fuel routing with heat isolators and other things to block the heat (shields, heat sleeves)
Click to expand...

I agree with this completely. Get that fuel hose and filter away from the top of the engine!
 
67Dart273 said:
A front pump is no damn good. You need to consider building a vapor return. Go dance around slant six . org. SOMEWHERE there is an article specifically on slants and fuel problems.

On mine, a 360 then 318, I finally went to EFI. "But before" that the best things I did was to go to a rear mount pump, vapor return system, and a nice carb isolator / spacer. Wix 33040 (5/16) or 33041 (3/8) filters have a 1/4" fitting with a return orifice

WIX-33040.jpg
Click to expand...

If you look at the picture closely, I think the original poster is running a setup like this. The routing off the filter goes to the 71 style vapor return hard line on the top back of the passenger side inner fender.

Were as the body long fuel hard line is supplied at the passenger frame rail down below.
 
Put a 1/2" fiber type spacer under the carb. That solved a problem a friend had with his slant. Also as mentioned by others here, isolate the fuel lines away from the heat sources.
 
Blackmamba said:
In Canada, only 91 and higher octane gas contains no ethanol. So more asking about ethanol and referring to how its not suited for old engines.
Click to expand...
OK, understood, it is different here; you can get several octane ratings with or without ethanol in some areas (mostly agricultural areas from what I have seen).
 
autoxcuda said:
Was that your fuel line routing before you added the electric pump?

In that picture your fuel line is resting directly on the heater hoses. And its laying on the valve cover and then routed all the way over to the intake manifold.

That's not right. And a potential safety hazard.

Most vapor lock situations can be solved without an electric pump. Just need a well though out fuel routing with heat isolators and other things to block the heat (shields, heat sleeves)
Click to expand...

lilcuda said:
I agree with this completely. Get that fuel hose and filter away from the top of the engine!
Click to expand...

Thanks guys.
*This is the new routing, I ripped out the original metal line that ran in the stock position near the middle with the clear coffee pot filter.
I will go ahead and snake the line closer to the firewall and fender panel.
Curious, where would you guys place it?
 
67Dart273 said:
A front pump is no damn good. You need to consider building a vapor return. Go dance around slant six . org. SOMEWHERE there is an article specifically on slants and fuel problems.

On mine, a 360 then 318, I finally went to EFI. "But before" that the best things I did was to go to a rear mount pump, vapor return system, and a nice carb isolator / spacer. Wix 33040 (5/16) or 33041 (3/8) filters have a 1/4" fitting with a return orifice

WIX-33040.jpg
Click to expand...

autoxcuda said:
If you look at the picture closely, I think the original poster is running a setup like this. The routing off the filter goes to the 71 style vapor return hard line on the top back of the passenger side inner fender.

Were as the body long fuel hard line is supplied at the passenger frame rail down below.
Click to expand...

This is true, good eye autoxcuda.
 
TrailBeast said:
It's true that ethanol does evaporate quicker, and that it boils quicker so it could add to the vapor lock problem.
Del posted about a return system and the filter/return.
If you are sure what is happening is vapor lock then that would fix it.

Running an Edelbrock carb are ya?
Click to expand...

yessir.
 
91 octane has less BTU energy than 87....did you all know that? The higher octane only relates to higher power if you increase the compression to suit the 91 rating, Same goes for 106 and all the others.
 
Blackmamba said:
yessir.
Click to expand...

How did I know? :D
A lot of us that run Edelbrocks have these kinds of issue's with ethanol fuel because they tend to heat soak easier than other carbs.
They act and smell like they are trying to flood, but once I put an A/F gauge on my car I noticed it goes as much as 2 full points lean when restarted on warmer days until it gets cooler fuel in it again.
The fiber spacer helped a lot, but didn't clear it up completely.
 
just my 2cents, I had same problem locking
I ran a cool vent hose 2 carb base problem gone .
for what its worth.
 
For what its worth, I would like to ask, what degree Thermostat are you running? I originally had the 195 degree thermostat, obviously hotter, so I swapped it to a 180 degree thermostat, stock for my 1970 198 slant six. I noticed a pretty decent difference in overall engine temperature looking at my temp. gauge.

I would also recommend making sure your cooling system is good to go, and your carb settings; mixture, idle speed, and all necessary filters are checked.

Heat shields, electric fan?, all recommendations on this page are perfect for your situation.

It sounds like a lot, but checking all these aspects in your car can save gas and money, and save you from aggravating hot start problems.
 
TrailBeast said:
How did I know? :D
A lot of us that run Edelbrocks have these kinds of issue's with ethanol fuel because they tend to heat soak easier than other carbs.
They act and smell like they are trying to flood, but once I put an A/F gauge on my car I noticed it goes as much as 2 full points lean when restarted on warmer days until it gets cooler fuel in it again.
The fiber spacer helped a lot, but didn't clear it up completely.
Click to expand...

Right again. Nothing like the smell of warm gas on a hot night in July.
 
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