Hot starting in carb cars

Well, the guy has opinions.

And he is misinformed.

Vapor lock occurs ONLY in a fuel pump, or line to the fuel pump. NOT in the carb, or fuel line to the carb. Our cars suffer from boil over in the carbs, not vapor lock

Boil over/perc causes flooding, vapor lock is lack of fuel making it to the carbs.

Vapor lock was really mostly a 1930s phenomenon with Ford motors having the fuel pump high up on the motor, causing the fuel to boil in the fuel pump or feed line when subject to the vacuum /suction from the pump. Suction just caused the fuel to vaporize at teh pump inlet, and it wouldn't pump. It also occurred on later vehicles when the fuel line inlet was restricted at the tank.

Perc is also not necessarily an ethanol caused problem. It never happened in the late 1980s or early 1990s with 10% EtOH gas in L.A.CA, I know, I was there. I never had perc in the 308 or any other carbed car, like happens now

Modern gas is just plain blended with a lower vapor pressure fractions so it vaporizes easier for better/cleaner burning, and lower VP fuel is NOT a problem with fuel injection, like all cars have basically had since the late early 1990s, so there is no issue, unless you run modern fuel in old cars..

Doug

 

PS: 87 octane ethanol gas perc's just as much as 93 octane ethanol gas.

Doug

 

https://www.iea-amf.org/content/fuel_information/fuel_info_home/ethanol/e10/ethanol_properties

Some info above.

Ethanol increases the boiling point of gas, not lowers it.

Doug

 

If it doesn’t fire up on a hot start with a little stab of the peddle to catch it , I use 1/2 choke on the 2nd attempt and immediately close it once it’s running .

I feel it’s not as easy ( 208 GT4 on 34 DCNF s ) to start with ethanol fuel than before .
Yes fully serviced, tuned , new plugs etc etc by a Ferrari guy .
The compression ratio on the 2.0 L is 9.8 to 1

The 3.0 L is lower 8.something to 1 , so I notice the octane deficiency more ,

 

You are correct, I may have misread that as boiling point, not VP.

Though look at page 2, here.

https://www.chevron.com/-/media/chevron/operations/documents/motor-gas-tech-review.pdf

It believe it shows vapor pressure of Etoh gas lower than regular gas on that graph at normal operating temps.

Looking at it more closely, though, the difference is fairly insignificant.between the two at normal operating temps

But, gas has been reblended over the past 30 years to account for use in FI engines vs carbs. Modern gas does not need the high atmospheric boiling point it used to have. Also.... Older motors often had thermostats at 180*F, taht was raised to 195* for emission requirements, which coupled with lower BP gasolines, causes fuel perc in carb'd cars.

And factor in cars not often driven, someone is driving around in June, with high VP gas put in the tank in February....

I am NOT a gasoline engineer, just a long graduated ChE who worked in steam turbine power plants, trying to remember things from 40 some years ago..

Doug

 

The gear ratios in the final drive are lower .Great for hills and circuit driving I am reliability informed by a Ferrari race car builder .They used to swop in the 208 final drive on twisty circuits because the 308 was longer , too long .

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You could try running 87 octane, but you might notice a difference in torque. It's not something you will notice right away depending on how low your fuel level is when you fill up. If you start noticing sputtering in 5th gear around 35mph, put in some 89 and it will stop.

 

I run 87 octane Calif gas in my 78 GTS US and have no problems. Don't know what kind of power it actually is putting out but it feels plenty strong. It has Pertronix ignition, has been re-jetted and has empty cats so it may run a little different than a completely stock GTS. As far as hot starts go if its set less than 1/2 hour I turn the fuel pump on for about 15 seconds to insure fuel in carbs then just turn the key. No pumping at all. If its been a while but still hot I pump it a couple of times and just touch the gas pedal. It starts right up. I am convinced that a engine doesn't need any more octane than it takes to avoid detonation or pre-ignition. With our low compression ratio and cam timing it will run fine on 87. For anyone who watches Motortrend TV they had an episode of Engine Masters that tested the difference between various octane levels and found no difference either in horse power or ignition timing.

Barry

 

Interesting discussion. A local Shell station offers non branded 102 Octane Racing Fuel. I filled up twice with this gas, however, the engine didn’t run very well. At speed and high rpm’s it was fine, lower in the rpm range, at traffic lights it was terrible. I have high compression pistons and thought that it would provide a benefit. Switched back to 93 Octane and it runs much better. 76 308. If have never had starting issues.