[Kenth]

Your test was totally irrelevant, a jar with fuel in room temperature and a caburetor on a hot recently turned off engine?
There is NO way the evoparation will be at the same rate.

Why do you think car manufacturers implemented the EVAP system?

[78w72]

FJ, I didnt miss the point at all... the point Kenth & I are making is pretty clear... that test doesnt represent the situation on a car, Im not saying fuel evaporates in 30 mins or an hour, or that something else might be going on if the fuel is gone in an hour or 2... but to show what happens in reality on a engine, a test needs to mimic that situation... put ~.5 oz in a small container the size of a q-jet fuel bowl then heat it to normal operating temps of an engine and see what happens, it may not evap in 1 hour but I would bet a dollar it evaps noticeably faster than a jar full at room temp. Nobody is overheating their carbs in the examples they give, like what I stated happens in 2 of my q-jet cars, all my cars run at ~180 in almost all temps... anything different is not a accurate test is all I was saying.

Another example of fuel evaporating is small engines like lawn mowers & snowblowers, they have small vented carbs holding 1 oz or so of fuel, the bowls are positioned downward so no leaks from the bowls can happen... after a few days they always need primed with the bulb to get fuel back into the carb so the engine will start, its part of the design so they know its an issue... maybe we can get a primer bulb for our cars too?

[Shiny]

I like the bulb idea... a manual mechanical pump!

Beyond the obvious "personal tolerance" for cranking duration, I think extended cranking isn't great for journal bearings. They need to spin to build an oil film. When stopped and at low rpm, they will effectively be metal on metal. The oil will reduce friction, but in general, I think running bearings without a hydrodynamic oil film is a bad idea.

I'm sure there was a design goal for maximum cranking time before starting. This was probably more about perception than technical considerations but I doubt they wanted a car to crank for more than 1 or 2 seconds under "normal" use. They certainly knew a car could sit for months and would take a long time to refill the carb, but this was not the "normal" scenario. Generally, if you buy a car, you intend to use it.

So here are my measurements from today.

This is a stock '70 350 with a '69 Buick QJ on a '71 cast iron manifold. The mechanical pump was new in 2023. The carb was repaired and set up by Shaker455 (Jeff) and both the choke and fast idle are close to "right". The battery is strong, the starter sounds strong. I think it has a 160 degree thermostat.

The car has NOT been started since Oct or November. This means the bowl was empty. I can't prove it, but it was empty. Evaporation happens.

I pulled off the air cleaner and left it off. I taped a thermocouple onto the carb base to monitor the temperature.

To start it, I pressed the pedal to set the choke and fast idle. Then I cranked in 3 to 4 second intervals, starting and stopping a timer each time. I pressed the pedal after every interval to give it a pump shot when gas made it to the bowl.

The carb base temperature when I started was 52 degrees.

It cranked for 16 seconds before firing. It took 4 pedal presses and started on the 4th cranking interval.

I let it come up to temperature by idling for about 20 minutes. The thermostat opened, the choke opened, all normal. Then I shut it off.

As Kenth reminded us, the carb base got hotter after I shut the engine off. When I shut it off, the carb base temp was at 84. After sitting for 45 minutes, the temperature had climbed to 108 and then started falling.

2 hours after shutting the engine off, I pressed the pedal and started it again. This time, it started instantly... it cranked for less than half a second.

So after 2 hours at elevated temp, there was still enough gas to start quickly. I have no idea how much evaporated, but the carb was NOT dry.

I will check again after 24 hours, then maybe a week, etc.. to see how long it takes to totally go dry again.... remembering it's winter, though...



Mike

[carbking]

Ethanol boils at 173 degrees F.

Most street gasoline boils around 160 degrees F. The ethanol DOES NOT BOIL OFF FIRST!

We run into this issue SEVERAL TIMES DAILY ON "TELEPHONE DAYS" !

Paraphrasing Dr. Werner Von Braun " one test is worth 1000 expert opinions"

Test by running your engine until it is at a maximum temperature; kill the engine, open the hood, and place your jar of gas (most bowls are 1 3/4 to 2 inches deep) on the hot intake manifold, and close the hood.

Go back in an hour.

Testing without the heat is a faulty test.

Jon

[carbking]

Different carburetors boil (or percolate) the fuel at different rates.

My experience as follows of "modern" carbs:

WORST - Carter AFB (I have two on my 390 CID HP)
NEXT -Rochester Q-Jet
NEXT - Holley 4150 / 4160, etc.
BEST - Carter TQ (thermoquad)

I do not have sufficient experience with the Autolites to comment, I try to stay within my field of expertise.

One other thing to consider: gasoline (fuel) composition is very different in various areas. Missouri's fuel is not the country's worst (that distintion belongs to Colorado), but Missouri fuel is pretty bad.

One other thing to consider: look at the compostion of the Carter AFB. The fuel valves are ABOVE the fuel level, there is no way for the fuel to syphon (unless the car is parked on its top) !
The AFB has NO passage for the fuel to leak, but it disappears! Magic ?

I think the Holley is the best of the non thermoquads because there is a layer of air beneath the bowl.

Jon

[Shiny]

I measured crank time again today.

Car had been sitting for 51 hours since I shut it off. It's not too cold here, so probably 45 to 50F in the garage during this time.

Took 14 seconds to start, again on the 4th "burst" crank interval.

So...

16 seconds cranking after sitting months
Instant start 2 hours later
14 seconds cranking 2 days later

The mechanical pump eventually gets it done, but this is too long for me. I will be adding a solenoid primer pump. I have replaced everything in the fuel system in the last 2 years so I'm not inclined to believe the carb drains from anything other than evaporation. I could be wrong, but doesn't matter... a primer will get fuel to the carb faster when it's empty.

Mike

[78w72]

Nothing wrong with using a primer pump for this type of issue if you have already changed everything for new... and dont want to invest any more time tracking down the cause.

2 days does seem like there could be more than just evaporation going on, especially at only 45°... but a pusher pump will be a fix or band aid to get around whatever the problem is.

Have you seen these pumps? Cheaper priced than the bigger carter electric pumps and quite a bit smaller. Read online of someone else using this for a primer pump, this one is cheaper than MSRP.

https://www.ebay.com/itm/28630334268...4&gad_source=1

[grivera]

Originally Posted by carbking

Different carburetors boil (or percolate) the fuel at different rates.

My experience as follows of "modern" carbs:

WORST - Carter AFB (I have two on my 390 CID HP)
NEXT -Rochester Q-Jet
NEXT - Holley 4150 / 4160, etc.
BEST - Carter TQ (thermoquad)

I do not have sufficient experience with the Autolites to comment, I try to stay within my field of expertise.

One other thing to consider: gasoline (fuel) composition is very different in various areas. Missouri's fuel is not the country's worst (that distintion belongs to Colorado), but Missouri fuel is pretty bad.

One other thing to consider: look at the compostion of the Carter AFB. The fuel valves are ABOVE the fuel level, there is no way for the fuel to syphon (unless the car is parked on its top) !
The AFB has NO passage for the fuel to leak, but it disappears! Magic ?

I think the Holley is the best of the non thermoquads because there is a layer of air beneath the bowl.

Jon

This is interesting- the 64 I previously owned had dual Edelbrock 625 cfm carbs, one with a choke. That car would start rather easily after sitting for 1-2 weeks - one to two pumps of accelerator max - the choke worked flawlessly. It had the factory fuel pick up and a mechanical fuel pump .

[Shiny]

Originally Posted by 78w72

Nothing wrong with using a primer pump for this type of issue if you have already changed everything for new... and dont want to invest any more time tracking down the cause.

Difficulty of diagnosing the cause is the challenge here, not the time. If there was a non-invasive and simple way to measure the seal on the pump check valve, this thread wouldn't exist. Similarly, if there was a non-invasive way to directly measure fuel inside the carb bowl, it would help. I measured my carb temperature, it's not excessively hot.

2 days does seem like there could be more than just evaporation going on, especially at only 45°... but a pusher pump will be a fix or band aid to get around whatever the problem is.

It takes a long time to cool down after shutting off so the residual heat is certainly a big contributor.

Several on the forum with direct knowledge and years of experience have chimed in and convinced me it's normal and it's evaporation.

A search found this 15-yr-old thread with the same info but lots of supporting statements:

https://forums.maxperformanceinc.com...ight=fuel+pump

I will say CO gas is now regulated to a lower RVP... like 7 to 9, depending on how the rules get bent.

Also, my car is filled with ethanol-free gas. I have no facts, but perhaps it is more volatile than typical pump gas ?? Anyone ??

Have you seen these pumps? Cheaper priced than the bigger carter electric pumps and quite a bit smaller. Read online of someone else using this for a primer pump, this one is cheaper than MSRP.

https://www.ebay.com/itm/28630334268...4&gad_source=1

Thank you for the link. That's a good price for a name-brand solenoid pump.

I'm going to use one of the Purolator/Facet Cube pumps shared earlier in the thread by Kenth. I won't be doing this for a couple months but that's the plan.

Mike

[grivera]

Originally Posted by 78w72

Have you seen these pumps? Cheaper priced than the bigger carter electric pumps and quite a bit smaller. Read online of someone else using this for a primer pump, this one is cheaper than MSRP.

https://www.ebay.com/itm/28630334268...4&gad_source=1

Will a pump like this free-flow when not activated? To be used as a primer pump only?

[HWYSTR455]

This entire thread is why I gave up and went efi.

Even if it's tbi, the 'owner experience' is just 'better'.

I suspect it's the same reason the OE engineers went that direction too, because carbs are certainly cheaper.


.

[Shiny]

I don't know about the Edelbrock pump but the Facet pumps as shared by Kenth allow flow-through when they are off. Edelbrock is probably the same.

Here are the Facet pumps (multiple lines) that allow flow-through:

https://www.pegasusautoracing.com/gr...ID=FACETSIPHON

I don't know how much of a restriction they will introduce, but it won't be zero. So these pumps may not make sense for high HP fed by a mechanical pump. For my car, unlikely to be an issue. I suppose you could always leave them running as long as they flow enough to support your engine.

These solenoid-style pumps apparently have relatively tight internal tolerances on wetted parts so they recommend a pre-screen filter. Facet sells a 70 u version that looks just like the filter with the Edelbrock pump. I don't like the setup using a rubber hose in a fuel line, so if I use a filter, it will probably be something with NPT fittings on both ends, like this, assuming the mesh is coarse:



The Facet pumps (at least the Cube line) can also be configured to block flow when they are off, but that wouldn't make sense as an inline primer for a mechanical pump:

https://www.pegasusautoracing.com/gr...ID=FACETSIPHON

Either the "Posi-Flow" or the "Cube" lines should work as a primer pump. There are more options available on the Cube line and they look like they are built well. I like the ability to choose max pressure and the claim of "self regulating". I think any solenoid pump will be self-regulating when dead-headed, but the range of available max pressures on the Facet line is more comforting than a generic claim of "5 to 7 psi" on many of them. I am squeamish about over-pressuring my carb and causing it to flood. This is apparently a common concern with mechanical pumps that also claim to have a 5 to 7 psi max but are then reported to deliver 10.

Mike

[grivera]

Originally Posted by HWYSTR455

This entire thread is why I gave up and went efi.

Even if it's tbi, the 'owner experience' is just 'better'.

I suspect it's the same reason the OE engineers went that direction too, because carbs are certainly cheaper.


.

I think both still have their place - the EFI in my bird has been great ever since I ironed out issues - it wasn’t always the case and has left me stranded. My concern with non-OEM EFI is if one breaks down it is definitely a tow home or to a shop - you ain’t fixing the computer on the side of the road. Assuming one uses points and all other factory replacement type parts, you can usually repair on the side of the road. Same with an in-tank pump - if that fails you will likely not have a spare for replacement and even if you do, you need to have an access door in the trunk like Larry (FormulaJones) has.

[Formulajones]

EFI isn't a bad way to go. It does present a possible road side scenario I guess if you happen to have an important sensor fail.
I have mine setup for certain scenarios just in case. As grivera mentioned I run a trap door in the trunk literally making fuel pump swaps a 30 minute deal.
I also keep a open loop tune in the program so the car runs without an O2 sensor. So if that fails and AFR's go wonky I simply load that tune and drive away.
Other sensors like TPS or CTS probably won't leave you stranded but keeping spares are easy enough if you desire.
Keep in mind the need to change an in tank pump is extremely rare. Millions of cars on the roads today use them, in fact I'd bet everyone here has a car in the fleet with it and don't even think twice about it. So this shouldn't be a huge concern for anyone really.
02 sensors can occasionally fail but if installed properly I find that to be a rare issue as well. They usually have problems when horrible tuning practices are used, bad placement, things like that.

I don't believe EFI should be considered a solution for other problems one is having like this whole fuel issue. As I've stated many times both of our dailys are carb and points and simply don't have these problems. EFI in many cases I've seen come through here have their own new problems, primarily from horrible installs, terrible fuel system setups, wiring that looks like a rats nest, 99 percent of this stuff being self inflicted. Which helps me to understand why one had carb problems in the first place lol.
Unfortunately it then gives EFI an undeserving bad rap. But EFI is pretty nice when done properly.

[HWYSTR455]

I've had that Terminator tbi setup on the 442 since like 2012, no issues. I drove that thing after a partial resto on the Power Tour. It was in my driveway for a while due to a module failure in the dual sync (FAST distributor), replaced it and drove it from my old house to my son's house which is an hour 45 min away. With crappy old gas in it too.

Holley uses (for the most part) GM sensors, so they are reliable. I do have a spare set for times of troubleshooting or long drive toolbox mode.

If you're running a mech pump on your Pontiac, pretty doubtful you will find a replacement at an auto parts store, that stuff just isn't stocked by most. And you still have to make it from a roadside to a parts store.

I don't carry a spare tire, so if i get a flat, I flatbed it home anyway. So I'm prepared to do so. I didn't want to put a door in the trunk so if a pump goes bad, I just drop the tank.

Usually when pumps go bad it's not an on/off thing, it slowly starts flowing less and less. You start getting bogs etc, so you can usually limp it home.

I ran carbs for years in the LeMans, and drove up & down the east coast and more, rarely had a problem, but most of that time I had an elec pump. I did at one point have an issue with an HEI that was eating coils, and carried coils with me, but eventually switched to an aftermarket unit. Problem solved.

It can go either way with a mech pump/carb or efi, so it's hard to make that argument. But I do understand some not wanted to switch. Me personally, I won't go back.


.

[Formulas]

Those little facet pumps flow in the hood of 32GPH and have 1/8NPT interface and the thought is that because it free flows when off its going to feed a 400HP engine??

For referance a 1/8NPT fitting works with 1/4 line or less a stock old GTO was 5/16 and marginal at feeding much over stock

[Formulajones]

I can't have something like that on any of the cars here. It's already a challenge to make the stock fuel system feed my bird that is built to run the pure stock class going high 12's. Last thing I want to do is make that thing suck through a straw. Let alone any of the cars that have a larger fuel demand.

Would need some sort of bypass line around it with a one way check valve and by the time I plumbed all that in an already tight space it would look like cobbled up junk.

Like I said, I don't find any of it necessary on any of our cars. Even ones that sit for longer periods. If I have something that requires more fuel supply (IE more HP) and don't have class rules dictating a stock pump then I go straight for an in tank pump and never look back. It's clean, it's simple, done right it'll feed over 1000 HP and doesn't care if you have less, and it's dead nuts reliable.

[Formulajones]

Originally Posted by Kenth

Your test was totally irrelevant, a jar with fuel in room temperature and a caburetor on a hot recently turned off engine?
There is NO way the evoparation will be at the same rate.

Why do you think car manufacturers implemented the EVAP system?

You and w72 need to read the whole thread to understand why I did it that way. Then you'll see the relevance. I even explained that in the last post about it. Like I said, you guys are more than welcome to post up any version of a test you want. Until then your comments are irrelevant and just a bunch of chatter. Get something up here we can all relate to. How hot are you getting the carb to create these problems? How hot are you running the engines? Bet ya got a heat cross over, lol. Wonder who has leaks or drain back they aren't aware of. Convenient to just blame fuel quality. You guys care to share anything relevant at all???

[78w72]

I understand why that test was done... was just saying it is not the same as on the car. Large jar of fuel at room temp vs very small q-jet sized container at a normal operating temp of an engine... 160-190, add a little for heat soak after shut off. That is the only real world comparison for a fuel evap test IMO.

Cant do a test like this here... my cars are in winter storage. I also mentioned that I dont think fuel evaporates in 30 mins or a few hours hours and that something else was going on for that situation.

I mentioned the temps for the example of my engines/carb, they run right at the T-stat rating, ~180 in the heat of summer city driving or at the drag strip for a lot of passes, some back to back. The car that does the evap/drain back the worst is the 500+hp E-head 72 firebird... with aluminum intake and no heat cross over, lol. 1978 Q-jet built by Cliff, carb leaks are unlikely, lines & pump are all relatively new, system will hold psi on the gauge after shut off for many hours if not over night. Car is parked in a garage, no charcoal canister system, just vented via the carb vent & tank is vented. Could have leaks Im not aware of but not worth it as my evap/return issues are very manageable, a few short crank cycles after sitting awhile or just drive the car every few days and its fine.

It obvious some do have this issue for whatever reason and they either live with cranking a little when needed or add a primer pump or go full electric. What causes the problems can be debated forever, but it does exist. Hope Shiny reports back if he tries a inline pump.

[Shiny]

Originally Posted by Formulas

Those little facet pumps flow in the hood of 32GPH and have 1/8NPT interface and the thought is that because it free flows when off its going to feed a 400HP engine??

For referance a 1/8NPT fitting works with 1/4 line or less a stock old GTO was 5/16 and marginal at feeding much over stock

Good point!

I get it and agree these little pumps will reduce flow.

How much? Who knows, but two check valves, a couple 1/8 NPT fittings and the recommended filter aren't going to help you feed a carbureted 400 hp engine at the drag strip.

Will they mess up a 250 hp? stock 350 on the street?

My mechanical pump is a Delphi MF0155. It is "rated" at 38 gph. But it's unlikely to deliver that once it's pulling through the pickup, down a long tube, through some fittings, and finally through the small carb inlet. Wouldn't it be great if any of these manufacturers published pump curves! Once you bolt any pump into a system with flow restrictions, they aren't going to deliver their "open" flow.

A good question to ask Facet (or any pump manufacturer)!! Think they will know what the pressure drop vs flow is when they are powered off?

Probably smart to ask before spending even a nickel on this.

Clearly nothing is simple and it's a lot easier to crank as long as it takes to fill the carb... regardless of where the gas goes.

Mike