460 requires cranking after sitting

[kramttocs]

Ok, I kind of hate to post this as the internet is full of posts about restarting a 460 when hot but I figure if I have my own thread about it, it will prevent me from just living with it. Also most of the threads are about slow cranking which isn't my case.

Rebuilt 460
Holley Quickfuel Slayer 600cfm carb
New Odyssey battery (850 cca)
All new 1/0 cables - Power and ground. Dedicated ground going to starter
PMGR Starter: Powermaster XS Torque Starters 9505. Wrapped in a starter blanket
Headers
1986 F250 with electric in-tank pumps

Truck starts immediately when cold or after a short time shut off like filling up at a gas station.

If I let it set though after being at normal operating temperature for a period of time [tonight it was around 40 minutes in Lowe's] I have to crank it for maybe 2 seconds before it fires. Usually on the first crank it sounds like it's going to catch but it never does (just gets my hope up). At that point I've stopped cranking since I thought it was going to start. I then have to crank again for the 2 seconds before it fires up and runs.
It's not a slow cranking at all. It turns over smooth and fast; it just doesn't fire right off.

I don't want to discount anything and happy to perform any tests but I feel pretty confident in the electrical components which leaves me with the carb/fuel. The coil and the pumps/relays are the only things that aren't new.

It's probably not worth noting but the truck was kind of like this back when I first got it and before the restore/rebuild. It didn't seem to care about cold or hot starts back then though. If you missed the first fire then you had to crank it for a bit. I say 'not worth' because that was a different engine and carb as well as full emissions setup.

The carb bowls have sight glasses and my fuel rail has a pressure gauge on it.

One post I read mentioned the fuel expanding in the bowls so I will check that via the sight glasses the next time right after killing it and before starting it.

Happy to provide any additional info and add more tests to the list.

[Gary Lewis]

I'm trying to figure out what the condition might be that is causing the extra cranking.  And it seems like it could be that the choke might be on but the engine not cold and not needing the choke.

So, have you tried to floor the throttle when you start it after 40 minutes?  That should kick the choke open, but it will also squirt fuel in via the accelerator pump.  Conversely, have you pumped the throttle, thereby sending lots of fuel in.  The results of these tests might be informative.

I'm thinking you may have just a touch too much choke.  But, it could be that the idle mix is a little lean and you don't quite have enough choke.

How does it run when it finally catches?  Does it act like it is partially flooded and has to run a bit to clear out?

[kramttocs]

Thanks Gary.

Great idea - it could very well be the choke. I haven't messed with it much so will check it out. Now that you mention it, the truck did the same thing when working on the A/C and my neighbor mentioned something about it possibly needing adjustment.

As is, when it finally catches there might be a little bit of a pop out the exhaust but otherwise it is good to go as soon as it fires. That single pop also occurs when cold starting so maybe that is an indicator of something? I'll try to get a recording of it this evening.

[Gary Lewis]

I would guess that the pop is an indication of too much fuel, with it pooled in the exhaust and getting ignited by the hot exhaust gas as the engine finally fires.

So that could be the choke.  Or, it could be gas dripping out of the carb, either due to too high of a float level or a leaking accelerator pump or power valve.

[BullnoseLuvr]

If a short soak doesn't cause it but a longer one does it could be vapor lock.  You can also be getting a lean pop.

Mark

[kramttocs]

I didn't think electric fuels pumps suffered from vapor lock?

Also to note I have a 1" phenolic spacer under the carb.

[Rusty_S85]

electric fuel pumps can, its high pressure EFI that isnt effected as bad as like the radiator boiling point is increased with pressure.  But a carb running a low pressure carb electric pump you could get vapor lock on the suction side or the pressure side.

[kramttocs]

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

[BullnoseLuvr]

You could give it a nice hot soak and check if you get a good squirt from the accelerator pump.  If none the lock is in the carburetor.  However, since you have a spacer the lock could be in the fuel line, which I assume is metal.  If that's the case it would start on the fuel in the bowl and then stall.

Mark

[Rusty_S85]

Id also check the fuel tank side as well.  Ive seen electric pumps added on the frame actually vapor lock on the suction side.

[ArdWrknTrk]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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?