Ranger16
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Wait, I thought we where talking about a mechanical fuel pump.
The fuel magically disappears from my carb!
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Ranger16
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THAT experiment is even better than mine. It explains a LOT. 
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Awesome. Love these mad scientist experiments.
That pretty much settles it, least to my satisfaction.
Hey wait, what percentage alcohol is your gas in this experiment?
It does it with my factory 2 barrel on my 318 Swinger and I don't usually buy ethanol fuel so not only do Edelbrock/Carter carbs have a problem.
idrivemopar
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Ours is up to 10%, and I think that's why the initial evaporation was more rapid than the later, I think that was the mostly ethanol going bye-bye!Awesome. Love these mad scientist experiments.
That pretty much settles it, least to my satisfaction.
Hey wait, what percentage alcohol is your gas in this experiment?
Ranger16
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One question about your experiment. Did you leave the cap on (with just the small open nozzle) to simulate the smaller vent opening in the carb? Obviously I didn't, mine was in an open plate the the evaporation surface was much greater. If not, I may try to duplicate your experiment while trying to keep the evaporation opening somewhat similar to what is on the car to get a more accurate indication of the actual evaporation rate...................unless you want to.
idrivemopar
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I did this with the main cap off, which is about 3/4 inch in diameter, which just so happens to be about the total diameter of the 3 vents on a thermoquad as each is 1/4 inch, so the area is roughly the same.
Ranger16
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khryslerkid
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I know you were inquiring about Sta-Bil and I knew there was a good thread on here. Good testimonials.
http://www.forbbodiesonly.com/moparforum/threads/gas-additives.118986/#post-910526904
http://www.forbbodiesonly.com/moparforum/threads/gas-additives.118986/#post-910526904
not so famous bob
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I read very few of these posts. My 505" wedge has a fuel disappearing problem too, it magically disappears from the tank!
ckessel
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Does the fuel disappearance coincide with lack of traction?
khryslerkid
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Here's one for you. After running the engine up to operating temperature yesterday, I shut her off and about fifteen minutes later I noticed this.
Carburetor must have been leaking down and found a gap in the intake gasket. I pulled the intake and installed one paper gasket above the tin pan. That took care of the intake leak, now to find out why the carb was leaking down.
After this last startup, I readjusted the carbs and they tuned in a little better than before. (No vacuum leak now) I've been watching down in the carb and so far I haven't seen any gas trickling.
This can be a reason why you would be loosing gas, all I have to do is figure out what's causing it. Don't need the cylinders getting washed with gas, though I've never had a rich condition when fireing it up either. I'm thinking the float bowl overflowing after shutdown. Sometimes, after shut down, I'll see pressure still reading on the fuel guage and it slowly bleeds down over a period of time. Maybe some gas is getting by the needle and seat? I have totally rebuilt both carbs and will be installing new jets in the near future so I'll test this out then.
Carburetor must have been leaking down and found a gap in the intake gasket. I pulled the intake and installed one paper gasket above the tin pan. That took care of the intake leak, now to find out why the carb was leaking down.
After this last startup, I readjusted the carbs and they tuned in a little better than before. (No vacuum leak now) I've been watching down in the carb and so far I haven't seen any gas trickling.
This can be a reason why you would be loosing gas, all I have to do is figure out what's causing it. Don't need the cylinders getting washed with gas, though I've never had a rich condition when fireing it up either. I'm thinking the float bowl overflowing after shutdown. Sometimes, after shut down, I'll see pressure still reading on the fuel guage and it slowly bleeds down over a period of time. Maybe some gas is getting by the needle and seat? I have totally rebuilt both carbs and will be installing new jets in the near future so I'll test this out then.
Maybe ur pressure is coming from cooling system? LOL, just kidding. Needle&seat is a good possibility or then we're getting back in to the petrochemical thingy again!! Maybe lower float level a 1/16 or so?
khryslerkid
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I don't think I'm getting a good accelerator pump squirt in that carb either. IIRC fuel can leak by a pump seal and drain into the chamber. They are new and I'm useing E free gas.
Float levels will be adjusted. Rebuilding these carbs, I found both of them way off!
khryslerkid
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I've heard and read that they will handle up to 10 lbs without any problems. I'm useing the Carter M6903 pump and according to my Summit gauge, located on the fuel rail, it ranges from 6 to 10 lbs. Less as the engine reaches operating temperature. The specs on the pump says 6 - 7.5 I don't know how accurate the Summit guage is. I would like to spend more on a better one. I've been contemplating useing a regulator, I might be running on the edge as far as pressure goes.
R/T
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Im lazy and since i prefer the reliability of mechanical pump over electric, i bought one of Rock Auto's high tork starters, crank it for 20 secs. give it a pump and voilà, the monster comes alive. Also love the stainless gas tank and fuel line.
Steve Garner
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New to the forums, but not new to this planet. Been a journeyman mechanic (before they were called techs)for almost 40 years and another about 7 years before I became a journeyman. Worked on these cars when they were near new (didn't work in a dealership so only saw them off warranty). Cut my teeth on carbs. That's all we had. So over the years you pick up a few things.
I don't know why the op has a hard start problem. I have some suspicions, but without more detail and a look see, I don't know. But I do know this. Today's fuel does not vapourize as easily as it used to. According to the fuel manufacturers, the volatility peaked in about 1985. This is by design.
Liquid fuel won't burn, it must be turned into a vapour. In carburated engines we use heat to vapourize the fuel. The exhaust routed through the crossover in the intake, sent there by the heat riser, warms the air/fuel mix and vapourizes the fuel. Engines are hard to start when they are cold, and run poorly until they warm up because the fuel isn't vapourizing. No engine heat at the intake. So we compensate for what just goes straight out the exhaust as unburnt liquid fuel by dumping an excess amount of fuel in. Now the little that does vapourize is enough to light. In cool/cold conditions you often can not get enough fuel in there just through the accelerator pump in the carb to get it to light. So to richen it even further we choke off the air. Causes a vacuum in the carb throat and draws in copious amounts of fuel with little air. Now we get it lit. We run extremely rich through the choke until the intake warms enough to start to vapourize the fuel.
Racing fuels start better when cold because they vapourize easier. That, and the higher octane rating is why we use them in racing. We want a cold dense air charge and a fuel that doesn't need much heat to vapourize it.
Cars built after 1985 don't need the heat or the choke because they atomize the fuel through a nozzle at 65 psi instead of drizzling it out a hole in a carb. The smaller droplets vapourize much easier. This is why they starting make fuel less volatile in the late 80's. Didn't need it to vapourize as easily and they could reduce the amount of fuel that evaporated into the air we breath.
A fully closed choke will draw fuel out of the bowl even when the level in the bowl has dropped down quite a bit. So even when you have lost some fuel to evap, a properly adjusted, fully closing choke will go a long ways in cold starts. On a 67 Corvette I just finished, it was extremely difficult to start, even on a 70 degree day. At a glance the choke looked closed, but it wasn't closed tightly. The repop choke stat was incorrectly calibrated. I modified it to close the choke tightly and it was a totally different car.
I know, as well, that a lot of people slack off their choke stats to get the choke to come off because they have removed or disabled the heat riser and they aren't getting enough heat to the stat to take it off fully when warmed up. This means less tension on the choke when cold. Can't have it both ways.
Whoa, long reply here. It's a complex subject.
Steve
I don't know why the op has a hard start problem. I have some suspicions, but without more detail and a look see, I don't know. But I do know this. Today's fuel does not vapourize as easily as it used to. According to the fuel manufacturers, the volatility peaked in about 1985. This is by design.
Liquid fuel won't burn, it must be turned into a vapour. In carburated engines we use heat to vapourize the fuel. The exhaust routed through the crossover in the intake, sent there by the heat riser, warms the air/fuel mix and vapourizes the fuel. Engines are hard to start when they are cold, and run poorly until they warm up because the fuel isn't vapourizing. No engine heat at the intake. So we compensate for what just goes straight out the exhaust as unburnt liquid fuel by dumping an excess amount of fuel in. Now the little that does vapourize is enough to light. In cool/cold conditions you often can not get enough fuel in there just through the accelerator pump in the carb to get it to light. So to richen it even further we choke off the air. Causes a vacuum in the carb throat and draws in copious amounts of fuel with little air. Now we get it lit. We run extremely rich through the choke until the intake warms enough to start to vapourize the fuel.
Racing fuels start better when cold because they vapourize easier. That, and the higher octane rating is why we use them in racing. We want a cold dense air charge and a fuel that doesn't need much heat to vapourize it.
Cars built after 1985 don't need the heat or the choke because they atomize the fuel through a nozzle at 65 psi instead of drizzling it out a hole in a carb. The smaller droplets vapourize much easier. This is why they starting make fuel less volatile in the late 80's. Didn't need it to vapourize as easily and they could reduce the amount of fuel that evaporated into the air we breath.
A fully closed choke will draw fuel out of the bowl even when the level in the bowl has dropped down quite a bit. So even when you have lost some fuel to evap, a properly adjusted, fully closing choke will go a long ways in cold starts. On a 67 Corvette I just finished, it was extremely difficult to start, even on a 70 degree day. At a glance the choke looked closed, but it wasn't closed tightly. The repop choke stat was incorrectly calibrated. I modified it to close the choke tightly and it was a totally different car.
I know, as well, that a lot of people slack off their choke stats to get the choke to come off because they have removed or disabled the heat riser and they aren't getting enough heat to the stat to take it off fully when warmed up. This means less tension on the choke when cold. Can't have it both ways.
Whoa, long reply here. It's a complex subject.
Steve
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