Carburetor question
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Joined: Dec 2008
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From: Plant City, Florida
Carburetor question
'85 F-250 300c.i. rebuilt motor, runs excellently. When not started for over 2 days, the carb requires priming. At that point it will run and start again as long as it is started before approx. 2 days of not running.
There are no obvious leaks around the carb area while or after running. The auto choke is not functional but the temp here is in the 80's. I would rather not disturb the engine by replacing the carb which could open up more issues.
There are no obvious leaks around the carb area while or after running. The auto choke is not functional but the temp here is in the 80's. I would rather not disturb the engine by replacing the carb which could open up more issues.
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From: Angier, NC
DING DING DING WE HAVE A WINNER!
If you do a search for this, more so in the 80 to 86 truck area, you will see this is common.
If I dont use my truck during the week for something it sits from Saturday when I do my weekly trash runs and maybe a show till the following Saturday.
I used my truck last Monday then sat till today for the trash run and I had to crank it longer than if I drove it yesterday.
Yep this is normal with today's fuel
Dave ----
If you do a search for this, more so in the 80 to 86 truck area, you will see this is common.
If I dont use my truck during the week for something it sits from Saturday when I do my weekly trash runs and maybe a show till the following Saturday.
I used my truck last Monday then sat till today for the trash run and I had to crank it longer than if I drove it yesterday.
Yep this is normal with today's fuel
Dave ----
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From: Southern California
Short answer-------- no!
Logistics Pro
Joined: Mar 2005
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From: tujunga, calif
Agreed, a common problem. I have a glass bowl Holley on my 223 six and I can monitor visually the evaporation which takes about 7 days. My 289 with an Autolite 4100 will only last about 4 days? My Y block 292 with a Hollley 390cfm will last 2 weeks, My 390 with Holley 600cfm will last 2 weeks also? It may vary on where you live and the fuel blend, and carb type. Here in Calif the fuel blend is different then the rest of the country..
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Joined: Dec 2007
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From: Boise, Idaho
Another one of the reasons I switched to the Holley Sniper on mine.
Modern fuels are just no longer formulated with carburetors in mind.
They'll work, but there's a number of issues, such as evaporation, and boiling at lower temperatures (which exacerbates vapor lock quite a bit).
Modern fuels are just no longer formulated with carburetors in mind.
They'll work, but there's a number of issues, such as evaporation, and boiling at lower temperatures (which exacerbates vapor lock quite a bit).
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Joined: Aug 2002
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From: Southern California
Another one of the reasons I switched to the Holley Sniper on mine.
Modern fuels are just no longer formulated with carburetors in mind.
They'll work, but there's a number of issues, such as evaporation, and boiling at lower temperatures (which exacerbates vapor lock quite a bit).
Modern fuels are just no longer formulated with carburetors in mind.
They'll work, but there's a number of issues, such as evaporation, and boiling at lower temperatures (which exacerbates vapor lock quite a bit).
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Return lines are your friend if you didnt already have one. Then insulating your fuel lines from the Road and heat sources.
Then if necessatry a fuel cooler(shouldnt)
A working check valve ( I believe pump should do this?) and then no excess pressure. may mean a regulator.
Then if necessatry a fuel cooler(shouldnt)
A working check valve ( I believe pump should do this?) and then no excess pressure. may mean a regulator.
FTE Legend
Joined: Nov 2015
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From: Angier, NC
Return lines are your friend if you didnt already have one. Then insulating your fuel lines from the Road and heat sources.
Then if necessatry a fuel cooler(shouldnt)
A working check valve ( I believe pump should do this?) and then no excess pressure. may mean a regulator.
https://www.youtube.com/watch?v=-t6geNGbEXM
Then if necessatry a fuel cooler(shouldnt)
A working check valve ( I believe pump should do this?) and then no excess pressure. may mean a regulator.
https://www.youtube.com/watch?v=-t6geNGbEXM
The OP is taking of fuel in the carb evaporating for sitting.
Put a little fuel in a glass jar and let it sit uncovered to see how fast it is gone.
Also note to help keep vapor lock at bay and why you dont hear of it on newer cars & trucks is the fuel system IS UNDER PRESSURE from the tank (in tank pumps) up to the motor.
Anything under pressure will boil at a higher temp. Look at your cooling system the cap is rated for something like 13 psi. so it will not boil at 212*
Now anything under a vacuum will boil at a lower temp. This is why the old fuel systems that have the fuel pump up front on the motor have vapor locks.
From the pump on back to the tank is not in positive pressure but a slight vacuum and it boils at a lower temp.
The return line dose help and can be found on cars as far back as the mid 70's that I know of.
The reason is the fuel dose not sit in the supply line long enough to heat up and boil as it is always moving.
What is not used by the motor is sent back to the tank, always moving.
Dave ----
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From: Southern California
I agree with above...but the issue is evaporation from the fuel bowl...... it's going to happen... here's why...
1. Gasoline has a flash point of -50 F (meaning it is now releasing vapors at this temp or higher)
2. Carbs are not sealed..... they function from vacuum...every port, jet, etc. so air does get access to the fuel bowl (unless it's a special application carb)
3. in colder climates, it takes a bit long to evaporate...hotter climates shorter time because the hotter it is the more vapors are produced... ie. the fuel breaks down faster from a liquid to a vapor
1. Gasoline has a flash point of -50 F (meaning it is now releasing vapors at this temp or higher)
2. Carbs are not sealed..... they function from vacuum...every port, jet, etc. so air does get access to the fuel bowl (unless it's a special application carb)
3. in colder climates, it takes a bit long to evaporate...hotter climates shorter time because the hotter it is the more vapors are produced... ie. the fuel breaks down faster from a liquid to a vapor
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Ford_250
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Jun 29, 2007 11:27 AM