460 requires cranking after sitting

[ArdWrknTrk]

Good to know. Will the pressure gauge on my fuel log provide any indication of that being the cause?

Scott, you're more than likely experiencing boil over.

Vapor lock doesn't explain why your bowls would be entirely dry (because this is not happening)

And, carbs have float bowls precisely because they create a constant reserve independent of the fuel pump.

they are at atmospheric pressure and it takes some time to run them dry.

It's not like like fuel injection, which relies on pump pressure to work.

But too much fuel (and vapor) does explain why the mixture is too rich to fire until you crank a little through.

Remember your bowl vents are inside the air filter also....

[kramttocs]

Scott, you're more than likely experiencing boil over.

Vapor lock doesn't explain why your bowls would be entirely dry (because this is not happening)

And, carbs have float bowls precisely because they create a constant reserve independent of the fuel pump.

they are at atmospheric pressure and it takes some time to run them dry.

It's not like like fuel injection, which relies on pump pressure to work.

But too much fuel (and vapor) does explain why the mixture is too rich to fire until you crank a little through.

Remember your bowl vents are inside the air filter also....

Jim - you're making a lot of sense.

I haven't used the truck in a couple days but have been thinking about this.

You are correct- the bowls aren't dry since after it cools it fires right up without any cranking or touching the throttle.

Since the carb has sight glasses it sounds like checking those after sitting hot for a bit is the next thing to do.

I also still need to check the choke.

I was hoping the 1" spacer would prevent this.

Could the float be too high?

Wondering if I should try premium for a few tanks to see if that has any impact.

[ArdWrknTrk]

Jim - you're making a lot of sense.

I haven't used the truck in a couple days but have been thinking about this.

You are correct- the bowls aren't dry since after it cools it fires right up without any cranking or touching the throttle.

Since the carb has sight glasses it sounds like checking those after sitting hot for a bit is the next thing to do.

I also still need to check the choke.

I was hoping the 1" spacer would prevent this.

Could the float be too high?

Wondering if I should try premium for a few tanks to see if that has any impact.

Gasoline expands a lot when it comes from the cool tank's underground.

Just look what happens to a jug when you fill it.

Now put it in the engine bay, where it's likely 200+ F.

The float valve works one way.

If fuel expands (or boils) it's going right into the intake.

Stochiometric is ~14:1 but it isn't going to light at 3:1.

[1986F150Six]

Gasoline expands a lot when it comes from the cool tank's underground.

Just look what happens to a jug when you fill it.

Now put it in the engine bay, where it's likely 200+ F.

The float valve works one way.

If fuel expands (or boils) it's going right into the intake.

Stochiometric is ~14:1 but it isn't going to light at 3:1.

Scott, as an experiment, drive the truck until it gets to operating temperature and park [like at Lowes] and immediately open the hood. Leave it open while you shop and then attempt to restart when you return.

[ArdWrknTrk]

Scott, as an experiment, drive the truck until it gets to operating temperature and park [like at Lowes] and immediately open the hood. Leave it open while you shop and then attempt to restart when you return.

That's a good idea David.

It would prove (or disprove) the "baking in its own juices" theory.

Sometimes the simplest diagnostics are best.

[ArdWrknTrk]

That's a good idea David.

It would prove (or disprove) the "baking in its own juices" theory.

Sometimes the simplest diagnostics are best.

When you think about it, even with the lean burn 4180 these trucks had A.I.R. injection into the exhaust manifolds to reduce hydrocarbons emitted at the tailpipe.

This leads to ferocious under hood temperatures, especially when stopped and you have 800# of scorching iron under the hood.

You can ask Bill. I'm pretty sure he'll back me up on this.

Anyway, that's my thoughts on why it won't fire right off after heat soak.

I don't think it has anything to do with vapor lock.

Although that can be an issue with mechanical pumps like mine, in over 30 years of ownership I've never had that problem.

[kramttocs]

When you think about it, even with the lean burn 4180 these trucks had A.I.R. injection into the exhaust manifolds to reduce hydrocarbons emitted at the tailpipe.

This leads to ferocious under hood temperatures, especially when stopped and you have 800# of scorching iron under the hood.

You can ask Bill. I'm pretty sure he'll back me up on this.

Anyway, that's my thoughts on why it won't fire right off after heat soak.

I don't think it has anything to do with vapor lock.

Although that can be an issue with mechanical pumps like mine, in over 30 years of ownership I've never had that problem.

Thanks David/Jim. That is a good idea and one I started to test this evening but then I went a little too far to really compare it apples to apples.

After work I checked the sight glass on the front bowl and I had to shake the truck to see that the level was below the glass. This was after I parked it in the shop and left the hood closed after the 30 mile highway drive home the other night.

Assuming it was right in the middle of the glass when I killed it, it seems like that is a lot of fuel to expand and overflow into the intake, then contract back down to below the sight but possible?

I'll mention here that when sitting at idle the fuel is right in the middle of the glass and the fuel pressure gauge on the log reads between 4.5 and 5 (no regulator, just the 86 electric pumps). The gauge is not liquid filled fwiw.

Also, after sitting long enough to cool the gauge goes down to 0.

I took the truck for a drive around town with ac on so it didn't take long to hit operating temp.

I then brought it back home, parked it and popped the hood. I wanted to see the glass better so I removed the air cleaner - played hot potato. Removing it is why I said it's not a great comparison to normal usage. While watching the gas rise in the glass I also noticed the pressure gauge rising. It went all the way to 12.5 before it stopped rising. At this point the fuel was about to the top of the glass. Not all the way to the top but close. Looking in the top of the carb periodically I never saw any fuel.

This was about 30 min after shutoff.

At this point I turned the key and the truck started right up, no throttle needed and no pop from the exhaust.

Going to 12.5 psi seems like a lot and I suspect it's even higher if the air cleaner was on and hood was closed. I thought the fuel vapor separator would prevent this and return some of the fuel to the tank but maybe not?

It seems like the sight glass may be a reliable and easy way to track this situation. Can do David's test and monitor it then repeat with the hood shut until completely cool.

 

[Gary Lewis]

Thanks David/Jim. That is a good idea and one I started to test this evening but then I went a little too far to really compare it apples to apples.

After work I checked the sight glass on the front bowl and I had to shake the truck to see that the level was below the glass. This was after I parked it in the shop and left the hood closed after the 30 mile highway drive home the other night.

Assuming it was right in the middle of the glass when I killed it, it seems like that is a lot of fuel to expand and overflow into the intake, then contract back down to below the sight but possible?

I'll mention here that when sitting at idle the fuel is right in the middle of the glass and the fuel pressure gauge on the log reads between 4.5 and 5 (no regulator, just the 86 electric pumps). The gauge is not liquid filled fwiw.

Also, after sitting long enough to cool the gauge goes down to 0.

I took the truck for a drive around town with ac on so it didn't take long to hit operating temp.

I then brought it back home, parked it and popped the hood. I wanted to see the glass better so I removed the air cleaner - played hot potato. Removing it is why I said it's not a great comparison to normal usage. While watching the gas rise in the glass I also noticed the pressure gauge rising. It went all the way to 12.5 before it stopped rising. At this point the fuel was about to the top of the glass. Not all the way to the top but close. Looking in the top of the carb periodically I never saw any fuel.

This was about 30 min after shutoff.

At this point I turned the key and the truck started right up, no throttle needed and no pop from the exhaust.

Going to 12.5 psi seems like a lot and I suspect it's even higher if the air cleaner was on and hood was closed. I thought the fuel vapor separator would prevent this and return some of the fuel to the tank but maybe not?

It seems like the sight glass may be a reliable and easy way to track this situation. Can do David's test and monitor it then repeat with the hood shut until completely cool.

Yes, I'd think the sight glass would tell the tale. The gas can't pour into the intake if the level stays low.

But that pressure rise is odd. Like you, I'd have thought that the hot fuel handling's orifice would bleed any pressure off almost as soon as you turn the engine off, and certainly not let it build up. In fact, I saw the pressure drop almost immediately when I turned the key off. But I never checked on buildup.

So, I think you have a blockage in your return. Not saying that it is the problem with the hot start as if the fuel level doesn't come up then that shouldn't be the cause. But.....

[85lebaront2]

Thanks David/Jim. That is a good idea and one I started to test this evening but then I went a little too far to really compare it apples to apples.

After work I checked the sight glass on the front bowl and I had to shake the truck to see that the level was below the glass. This was after I parked it in the shop and left the hood closed after the 30 mile highway drive home the other night.

Assuming it was right in the middle of the glass when I killed it, it seems like that is a lot of fuel to expand and overflow into the intake, then contract back down to below the sight but possible?

I'll mention here that when sitting at idle the fuel is right in the middle of the glass and the fuel pressure gauge on the log reads between 4.5 and 5 (no regulator, just the 86 electric pumps). The gauge is not liquid filled fwiw.

Also, after sitting long enough to cool the gauge goes down to 0.

I took the truck for a drive around town with ac on so it didn't take long to hit operating temp.

I then brought it back home, parked it and popped the hood. I wanted to see the glass better so I removed the air cleaner - played hot potato. Removing it is why I said it's not a great comparison to normal usage. While watching the gas rise in the glass I also noticed the pressure gauge rising. It went all the way to 12.5 before it stopped rising. At this point the fuel was about to the top of the glass. Not all the way to the top but close. Looking in the top of the carb periodically I never saw any fuel.

This was about 30 min after shutoff.

At this point I turned the key and the truck started right up, no throttle needed and no pop from the exhaust.

Going to 12.5 psi seems like a lot and I suspect it's even higher if the air cleaner was on and hood was closed. I thought the fuel vapor separator would prevent this and return some of the fuel to the tank but maybe not?

It seems like the sight glass may be a reliable and easy way to track this situation. Can do David's test and monitor it then repeat with the hood shut until completely cool.

I agree with the pressure should not rise (I never checked my pressure) I never had a hot start problem, but I had the Holley 4180 on with all of it's affiliated plumbing until I went to EFI.

One of the things the factory bowl vent system did, the external bowl vents (on mine) were closed by vacuum with the engine running and opened to the evaporative canisters through 2 3/8" diameter vent hoses with the engine shut off. What bowl vent system does the quick fuel use, strictly into the air cleaner or is there any provision to vent to the canisters?

Your test seems to confirm my thoughts, the heat is evaporating some of the fuel and the result is the air filter is now loaded with a rich mixture that even holding the throttle down won't clear. You have to crank it until enough fresh air is pulled in.

On the pump system, I used to "hot wire" the pump by taking the blue fusible link off the relay pin and touching it to the battery terminal on the relay until I heard the "hiss" of gas in the return orifice. I would remove the separator and blow air through the return port and see what comes out of the inlet or outlet ends.

[Gary Lewis]

I agree with the pressure should not rise (I never checked my pressure) I never had a hot start problem, but I had the Holley 4180 on with all of it's affiliated plumbing until I went to EFI.

One of the things the factory bowl vent system did, the external bowl vents (on mine) were closed by vacuum with the engine running and opened to the evaporative canisters through 2 3/8" diameter vent hoses with the engine shut off. What bowl vent system does the quick fuel use, strictly into the air cleaner or is there any provision to vent to the canisters?

Your test seems to confirm my thoughts, the heat is evaporating some of the fuel and the result is the air filter is now loaded with a rich mixture that even holding the throttle down won't clear. You have to crank it until enough fresh air is pulled in.

On the pump system, I used to "hot wire" the pump by taking the blue fusible link off the relay pin and touching it to the battery terminal on the relay until I heard the "hiss" of gas in the return orifice. I would remove the separator and blow air through the return port and see what comes out of the inlet or outlet ends.

Bill - If the problem is that the air in the air cleaner is loaded with gas, how about testing with the air cleaner off? Or, pull the lid and let it clear out and put the lid back on to start?