Starting Problems with 356C

[David Jones]

Martin,
That would not work, the practical way to do it would be to fire up the engine and once it is running on all four cylinders then shut it down before the heads got really hot, then wait two days and then try and start the car. Part of the issue is that winter gas has an initial boiling point of 65*F so if the car is shut down hot then it will evaporate faster. An open cup exposes more surface area so again the fuel will evaporate faster. Modern cars have sealed systems so no fuel is lost to evaporation and fuel injection takes care of cold starts. We have a situation where we are using fuel that is a compromise. If there were not so many vehicles out there with carburetors we would have a whole different composition of gasoline. We have to live with it and put in our own workarounds like supplementary fuel pumps and priming bulbs or just make sure you have a good battery and crank it till the oil pressure light goes out then pump the gas pedal till it starts. One thing nobody mentions is that I suspect this problem occurs more with cars that have the older fuel tanks under the hood as they are set higher so fuel level is more likely to stay up on those cars. I do believe both my "A" cars start faster than the "C".

[Charlie White]

And I would guess that this happens in Arizona because we
have higher average daily temperatures AND lower average
daily humidity! Using a "priming bulb" in the engine compartment
also scares me - more fuel line connections in the engine compartment
to leak gas, and a rubber priming bulb to dry out and leak!

CW

[Martin Benade]

I feel pretty confidant that the carbs are leaking on some cars (such as mine) because this starting problem is one that some people have and many do not. David, did you mean 165' F? 65' F seems way too low. My suggestion was for a VERY rough estimate/test, not accurate at all but might give a clue. If you do your test on a cool engine, then you cannot tell whether the fuel leaked down or evaporated up. Evaporating from a semi-closed Zenith would happen much slower that the open cup I suggested, but I doubt the open cup would be empty in 2 days, although I have not actually tried it.

[David Jones]

Martin,
I did mean 65*F. Summer grade gasoline does not start to boil until 95 *F for obvious reasons. These numbers are normal for Northern states and were what we formulated gasoline for at the refinery where I worked in Ohio.

[Martin Benade]

So if I saved some winter gasoline and put it in a bowl on a 70 degree day in the spring it would literally be in a rolling boil like water in my teapot? How about a full tank? Would enough things evaporate in a couple of months between now and spring that nothing crazy would happen? Asking these questions make me realize that my car sitting in the sun all day on a 100 degree day certainly does not have its gasoline boiling, when the tank is surely above ambient temp.

[Fred Gruendig]

Charlie,
I can understand how the rate of evaporation is affected by ambient temperature but you seem to also stress "lower humidity".
Could you please explain how low humidity (amount of water vapor in air) would increase the rate of gasoline evaporation?
Thanks,
Fred

[David Jones]

Martin,
Quick explanation is that gasoline is composed of many different crude oil fractions which all have different boiling points. They start at 65 for winter gas and at 95 for summer gas. The initial boiling point is where it starts to boil and the final boiling point is where the last fraction boils off which is regulated to be 427*F in the main.
The 50% point is about the temp of the heads at working temperature so on shutdown until the heads cool off the heat that percolates to the carbs is actually boiling off the gas. This does not happen in fuel injected systems because the fuel is under pressure and it then take higher temps to make it boil.

[Charlie White]

Fred,
Technically, I have no clue! My supposition is that the lower
the humidity, the less water is in the air, the dryer the air is,
hence more evaporation. If someone has a more technologically
correct answer, please chime in!

CW

[David Jones]

Charlie it should make no difference. The modern gasolines are more volatile then 60's era gas and will evaporate a lot faster. If you do as Martin suggested you will find it will all evaporate quite quickly and in Arizona much faster than Ohio as your ambient temps are a lot higher.

[Charlie White]

Are you saying that temperature and humidity have
no effect on evaporation?

CW

[David Jones]

Temperature yes but humidity no. Humidity will affect water evaporation but not gasoline as gasoline will not mix with water. Surface area as well as temperature are the main factors governing evaporation in this circumstance. A saucer of gas will evaporate faster than the same amount in a tall glass at the same temperature.

[Charlie White]

"A saucer of gas will evaporate faster than the same amount in a tall glass at the same temperature."

I assume because there is more surface area in a saucer than in a tall glass?

CW

[JohnLiles]

Hi Charlie , yes , more surface area = more evaporation . However (!) , evaporation from a tall glass will be dependent on where the liquid level is in the tall glass...if the liquid level is well below the rim of the glass , this will lead to less evaporation than if the level were close to the top of the glass because of mass transfer effects , diffusion versus convection . Which is irrelevant to our carburettor bowl.

The composition of the fuel we use today is not the same as the composition of the fuel we used when 356C was in manufacture , one of the reasons is the presence of ethanol , but David Jones probably knows more than me about this. My '63 S90 used to stand around in the 70's for days at a time without being run and with no battery conditioner but my memory is that it was easier to start than my '64 C nowadays which always has a battery conditioner attached.....OK ...the C stands around for weeks at a time so not a true comparison

[Jon Schmid]

OK, I guess at this point, I'm in punt formation. Wyatt's first sentence: "Lately, I have been having a very difficult time starting my engine after the car sits for only 2-3 days." Everyone is dancing around with evaporation issues but I ain't buying it. Weeks, OK. Days, umm... no. Wyatt, have you done a full tuneup yet? What is it, 80% of all carburetion problems are ignition related? Unless your car reeks of gas from a hemorrhage of fuel, I would check that out first--and I am far from an expert, but I do have a lot of history on both my cars. Don't forget the valve adjustments. Give it a try.
Best of luck--I look forward to finding out what you see.
Jon

[Wyatt Blankingship]

I want to thank all of you who have posted replies to my starting issues. For the last two days I have been checking the fuel level in the bowl of the driver side Zenith carburetor after bemoving the top of the carburetor. I also removed the float to make it easier to check the level. In the 1st. 24 hours the level went down 6.5 mm(.256"). In the second 24 hours the level went down another 4 mm(.157"). This is what I believe is happening. I have a very slow leak where the pump suction valve or the pump pressure valve or possibly where both screw into bottom of the carburetor. I believe that the amount that leaked out the second 24 hours was less than what leakead out the first 24 hours was because the level had dropped the second day. Lower level = less pressure. I do not believe that there is a significant evaporation problem. Although I live near New Orleans the temperature in my unheated garage has been a high of 60F during the level test. I tried to remove the carburetor and gave up in spite of having the proper wrenches to do the job. Too much for this 77 year old body with disc problems. Since the fuel leak is so slow I do not believe that there is a fire issue if I leave everything as is and install a priming bulb to fill up the bowls before cranking the engine. If anyone has any other ideas/suggetions please send out a post.
Thanks much again, Wyatt Blankingship
Happy Mardi Gras!