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Old 03-04-2018, 05:07 PM
jarretts70 jarretts70 is offline
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Default Quadra-jet loses fuel while sitting.

I'm struggling a bit with the last couple tuning issues with my quadra-jet. It's a 1978 T/A W72 carb (original to my car) on a reasonably stout 428.

My issue is that I lose all the fuel out of the fuel bowl if the car sits for more than a few days. If I start it every day or two there is no problem, it starts as well as my late model Chevy truck. If it sits for 5-6 days its hard to start. If I let it sit more than a week, forget about it. I could crank it all day....I use a squirt bottle of gas to prime the carb and it starts right up.

The last time I had it started was about 3 weeks ago. Today I pulled the carb & carefully took it apart, so as not to spill any remaining fuel. It was bone dry; as well, there was no fuel sitting in the intake plenum.

When the carb was rebuilt I re-sealed the plugs with marine epoxy - I don't think they are leaking. But I can't figure out where the gas is going. Any thoughts?

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Old 03-04-2018, 05:26 PM
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The plugs could be leaking and the gas will evaporate faster with the ethanol content
Also, how old is the fuel pump and what's the float level set to?

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Old 03-04-2018, 05:26 PM
Formulas Formulas is offline
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It shouldnt take any more than about 5 seconds of cranking and foot stomping to start our stuff with a good mechanical pump and no cracked rubber lines with a dry bowl

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Old 03-04-2018, 05:51 PM
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pretty sure thats a common issue, even without plugs leaking or ethanol in the fuel. gas does evaporate & the q-jet fuel bowl is very small.

i have 2 of the same 78 t/a q-jets in use on my cars that were both rebuilt by cliff r, both do the same thing after about 4-5 days of sitting. i dont use fuel with any ethanol.

my routine for when the cars sit that long is to just crank the engine for about 5 seconds to prime the pump/carb, then pump the pedal a few times to squirt some fuel & set the choke, it starts right up.

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Old 03-04-2018, 06:18 PM
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What you're experiencing is normal with todays fuels, ethanol laced or not. I have an electric pusher pump out back by the tank that helps after a long non-running spell.

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Old 03-04-2018, 07:35 PM
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I agree with everyone else. It's evaporation. I have the same issues with all my cars equipped with Q-jet carbs if I let them sit over three or four days.

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Old 03-04-2018, 07:41 PM
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Yeah, modern gasoline's evaporate sooo easily. I was working on a 2 Bbl carb for a friand. I set it in a small steel bucket that had enough capacity to completely submerge that carb. I let it set for a couple of days, that helped with all the slime and grime, inside and outside...

I left the dirty gas in the bucket, put a 5 gal bucket over top, to keep the dirty gas from evaporating.........I needed to move that bucket of gas 3 month's later, it was completely gone...

I don't drive my 77 T/A much. Something I learned from an old job (we had lot of old gas powered buses that sat around for a long time between starts..
I pump the throttle to set the choke, then crank the engine for 5-10 seconds, some times it will maybe hit on one cylinder, I then turn ign swi off, THEN pump accelerator 3-4 times, it usually firs right off. The point being, will that carb with gas before you utilize the acc pump to get the extra needed in engine to start.....

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Old 03-04-2018, 07:41 PM
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Same here.

When having sat several days, crank it a bit then pump the throttle several times.

When having sat only a day, one or two pumps and she fires right up.

When warm, don’t even have to touch the throttle most times.


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Old 03-04-2018, 09:08 PM
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If the carb is already off, it would not hurt to test the plugs for a leak.

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Old 03-04-2018, 09:34 PM
jarretts70 jarretts70 is offline
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The car had a full-bore resto, so everything is new from the gas tank to the carb. That said, the fuel pump was nothing special, just a stock style replacement. To be honest I don't even remember what brand it is. I was trying to keep everything looking pretty stock....

I'll check the plugs just to be sure....I didn't realize that modern fuel was that prone to evaporation. I run 91 octane pump premium which is supposed to have minimal ethanol content, but it's hard to find anything without at least some ethanol around here....

I've tried the pump gas once/crank/shut off & pump gas multiple times/crank thing, but I have to repeat it many times, and crank the heck out of the thing. Sometimes it works, sometimes not...If I prime it then it starts easily so that's what I normally do.

One other thing that might(?) be related - when I shut the car off after it runs for more than a few minutes I can hear gas running back into the gas tank. Residual fuel left in one of the return lines? Not sure if this is normal or not.

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Old 03-04-2018, 09:55 PM
jarretts70 jarretts70 is offline
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FWIW, I've been thru the carb a few times. When I first got the car running the tune was way off. Idle mixture screws did nothing/ bad hesitation issues/ dirty spark plugs/ etc.

I bought Cliffs book - between that and advice on this forum I've got it running well. Idle circuit mods & air valve adjustments were all it took. Idles great, cruises great, good throttle response. Even gets reasonable gas mileage. Two remaining issues:

1 - After 2-3 seconds of WOT it runs out of fuel & I have to lift. Raising the float level helped a little but did not cure it. Float is set at 1/4" below the top of the airhorn. I'm installing a windowed needle & seat to see if it makes a difference.

2 -The starting issues.

The fuel starvation at WOT and the seeming inability to refill the fuel bowl when trying to start have got me thinking maybe my new fuel pump is not up to scratch?

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Old 03-04-2018, 10:07 PM
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Having problems at WOT now has me leaning toward a fuel pump volume issue. Yes the Q-jet bowl is small, but with the stock 3/8" line, there should be sufficient fuel available to run the car to the factory red line. The fuel you hear going back to the tank I suppose could be leaking past the valves in the fuel pump. The valves could also be leaking during running, unable to maintain fuel in the bowl. The fuel pump won't cure the bowl fuel loss of course, but as said an empty bowl Q-jet should fill and start the engine in 2, 5 second crank intervals. My next move would be to verify fuel pump pressure and flow, or just replace it.

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Old 03-05-2018, 02:51 AM
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I have always gotten good service out of Edelbrock mechanical fuel pumps

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Old 03-05-2018, 04:23 AM
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Got the same starting/WOT issues 25+ years ago.
Replaced the mech fuel pump with a Carter P4594 mounted close to fuel tank, never looked back.

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Old 03-05-2018, 08:14 AM
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Evaporation is normal with any carburetor and this new fuel for sure doesn't stick around very long.

However it should re-fill very quickly and you should never have to prime it with fuel. I'd be wondering why all the fuel in the lines are draining back to the tank and even if they did why the fuel pump isn't picking up the fuel and filling the carburetor with a reasonable amount of cranking time.......Cliff

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Old 03-05-2018, 08:27 AM
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Agree with all the above and I will add that we are all spoiled by fuel injection in today’s vehicles so we feel like we are cranking so much on our old cars.
Do a flow test on your pump.

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Old 03-05-2018, 10:44 AM
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I'd add here that for quite a few years I owned a 1985 Caprice with a 305 carbureted engine. It didn't see much use and would sit for weeks and often months at a time. No matter how long it sat, it required two and at the very most three 4-5 second cranking sessions while pumping the throttle at the same time. It would then roar to life on the fast idle. Most of the other carburetor GM vehicles I've owned over the years were about the same way, and all of them would roar to life instantly if restarted within 1-2 days of sitting....FWIW......Cliff

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Old 03-05-2018, 12:16 PM
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Default Just rambling thoughts

Quote:
Originally Posted by jarretts70 View Post
The car had a full-bore resto, so everything is new from the gas tank to the carb.
Questions about this later.
Quote:
Originally Posted by jarretts70 View Post
That said, the fuel pump was nothing special, just a stock style replacement.
Changed the mechanical pump on my 79 a few years ago. Sitting level, with a full tank of gas, I had to plug the line to the tank to keep fuel from running out. It siphons out because the line up front is lower than fuel level in the tank.

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Quote:
Originally Posted by jarretts70 View Post
.I didn't realize that modern fuel was that prone to evaporation.
Think about how big the bowl is and how much of that is displaced by the float. Carbs stay cool when the engine is running. Heat soak after you cut it off, especially with a functional exhaust cross-over, and not all but most of the gas will evaporate in a hurry.

Quote:
Originally Posted by jarretts70 View Post
One other thing that might(?) be related - when I shut the car off after it runs for more than a few minutes I can hear gas running back into the gas tank. Residual fuel left in one of the return lines? Not sure if this is normal or not.
The 79 gave me more trouble with fuel starving (after engine upgrade) Than any Pontiac I've ever owned. Electric pusher helped a lot but it still happened at the worst possible times. More gas the tank had in it...the fuel starve happened more often.
Smog era tank vent does not let enough air in the tank for what gas is coming out at WOT. Fuel pump was pulling a vacuum in the tank. Worse when full (because of less air space) and fuel would cover the vent line making it harder to let air in.

Adding old school vent and vented cap stopped the vacuum in the tank that the fuel pump couldn't over power.

On your car...Vacuum in the tank would/could be pulling fuel out of the pump through the return line when you cut it off. The factory vent line can also get fuel in it when the tank is full.

A lot of cars, sitting parked, would actually flood the carbon canisters when conditions were right. Like cutting the car off right after fill-up on a hot day. A nasty wet carbon canister will barely let any air go back to the tank.

Just some past expierence with this
Clay

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Old 03-05-2018, 01:47 PM
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Quote:
Originally Posted by "QUICK-SILVER" View Post
The 79 gave me more trouble with fuel starving (after engine upgrade) Than any Pontiac I've ever owned. Electric pusher helped a lot but it still happened at the worst possible times. More gas the tank had in it...the fuel starve happened more often.
Smog era tank vent does not let enough air in the tank for what gas is coming out at WOT. Fuel pump was pulling a vacuum in the tank. Worse when full (because of less air space) and fuel would cover the vent line making it harder to let air in.

Adding old school vent and vented cap stopped the vacuum in the tank that the fuel pump couldn't over power.

On your car...Vacuum in the tank would/could be pulling fuel out of the pump through the return line when you cut it off. The factory vent line can also get fuel in it when the tank is full.

A lot of cars, sitting parked, would actually flood the carbon canisters when conditions were right. Like cutting the car off right after fill-up on a hot day. A nasty wet carbon canister will barely let any air go back to the tank.

Just some past expierence with this
Clay
Interesting info to have! Thanks for posting this, I think it may be applicable to my problem.

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Old 03-05-2018, 04:36 PM
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Don't pump the pedal at all before cranking it. Crank it for several seconds at a time. You need to pump gas all the way from the tank to the carb. as even the fuel lines can completely drain after a few days. If your car usually starts easily, once you get fuel to the carb, just a single pump of the pedal should start it if your choke is set right.

An electric pump near the tank would help. Run the pump on a switch for a few seconds to fill the lines and fuel bowl before trying to start. Then again, one (possibly two) pump(s) of the pedal before turning it over should be enough.

If you don't want to add an electric pump, you will eventually learn exactly how long you need to crank it before starting. I've had this issue with both Holleys and qjets.

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