Hello Again,

Since I've got some time thought I'd share this recent phenomenon with carbs and fuel quality, heat and altitude.

Recently I completed an intake and carburetor replacement on my '73 convertible. I went from a failing Quadrajet and a low profile dual plane late 60's cast iron LS5 intake to an aluminum dual plane air gap intake and Quick Fuel 750 carburetor.

Now a little back story I never had a problem with the cheap fuel up here with the old Q-Jet carb. It wasn't till I put on the Holley style carb that makes me now consider fuel injection very seriously.

The Q-jet has been on my car for 20+years. I could never get the idle mixture right on the car, it either stumbled lean or ran fat and eye watering painful. But credit where credit is due I never had to touch the carb for over 20 years. Well recently it finally said enough was enough (all the rubber parts finally died). On that note I bought the newer high rise aluminum intake and Quick Fuel carb, both brand new. I wanted something I could adjust easily and tune the engine, unlike the Q-jet.

I complete the swap and it was a cool evening and it started right up and needed virtually no adjustments. I was shocked for something right out of the box, the fuel level was centre'd in the windows, the idle speed spot on, the accelerator pump spot on. We went out for a 50 mile cruise in the cool evening hours with the top down and it ran like a champ. No more eye watering exhaust and it sipped fuel.

Next morning, still coolish, just starting to warm up, I do an errand. All is fine. Starts right up on the choke and doesn't miss a beat. I come back. It heat soaks in the now warming garage. An hour later it's hot and I need to do another errand. It cranks and doesn't want to start.

It finally starts and runs really erratically. I set the engine to about 2500 RPMs with my foot on the pedal and after a minute it's fine. However every time I give it fuel it feels like the accelerator pump is not working. I drive it for another 5 minutes and now that's working too.

I thought this is weird. What's going on.

I get out do some grocery shopping, again car won't start. I will mention it's hot, I have the top up and the massive air con running when I'm driving. Again, finally get it started and same thing all over again.

I come home, start taking in the groceries and I hear a loud thud, like an old metal garbage can oil canning. So I put my ear closer to the car and I notice the whole thing sounds like a coffee maker. I'm thinking what the....

For funsies I lift the license plate and start unscrewing the fuel cap and as soon as the last tang cleared it shot out about 3 feet. Another thud was heard from a relaxing fuel tank. So then I open the hood remove the air cleaner and both bowls are empty. Nein. Nada. Nyet.

I try to start it. Again it cranks for a long time then stumbles into life begrudgingly. I see fuel bubbling out of the vents from the carb from the opening in the open hood. I get out and look into the carb windows and it's boiling in the bowls.

My engine is not overheating, granted it's very hot out, add in heat soak from a big block with an air con cranked and the carb is too hot for the fuel. It looked like our side loader washing machine running when it started in the carb windows.

So it turns out obviously I ended up with fuel with a high alcohol content, add a hot day and 6500 MSL altitude and alcohol boils off at a low temperature. It wasn't until I ran the car and held the RPM's up the massive engine driven fan (aka leaf sucker) cooled the carb down enough that the fuel wouldn't boil.

I've since put the top grand in the car twice now and it's much better, but when it's hot, it acts like there's no accelerator pump. This took a moment to suss out. On a Holley style car the accelerator pump housing will not refill on its own if the fuel boils out of it. It requires the throttle to be active to refill the pump housing. So naturally it boils out, you give it some beans and it stumbles, it refills and if you give it the beans again, it's fine. But cruise for a bit, it boils and you're back to square one.

As much as I hate the Q-Jet, credit where credit is due, once the throttle is relaxed, if the fuel boils it automatically refills and so you do not miss a squirt. The other fun fact I had never considered is that the Q-jet keeps its fuel in the centre, next to the venturi's, that get cool from air passing through them. So it actually chills the fuel down on hot days and even the crappiest of fuel up doesn't phase it. Yuppers it boils out of the tiny Q-Jet bowl, requiring 3-4 seconds of cranking but it quickly fills and you're back in action. The Holley keeps it's fuel away from the cold bits and the darn front boil with accelerator pump is right in the path of the big angry fan blowing really hot air.

As a result I have concluded it's impossible to have a Holley carb in these parts anyway for these reasons. I can't control the quality of the fuel, especially when I'm putting in the top grade sold here. I could do AVGAS but it's pretty darn pricey.

I did suck out most of the heavily laden alcohol fuel since I had a full tank and I put that in our '96 Impy and it ran just fine on it. Why.... fuel injection. With that no more carburetors on old cars I have determined. It's a shame I had to learn the hard way. But I thought I would share it with you.

I will run the old tractor on AVGAS, because I do not use it that often and the extra expense of the fuel won't be a problem.

Just thought I'd share....

Rant 2

The car is equipped with a plumbed and functioning charcoal canister and the release vent is in the gap cap, which is also new. I do not have a gas cap pressure tester, but the fuel tank holds pressure like any of our other cars on really hot days and you release the fuel cap. Pretty much same thing, it'll shoot out if you're not careful and you'll end up with a face full of fumes.

I have also heard fuel boil in my Grand Marquis tank on really hot days in town. This is just the first time I ever noticed it in the convertible.

The convertible weirdly does not suffer from the more common definition of vapor lock, where the fuel boils between the tank and pump. The pump always draws fuel with no problems, it just boils in the carb and more importantly boils in the accelerator pump portion leaving hesitation from a stop. The problem is really exacerbated with the air con on full blast. Whilst it's like a meat locker inside the cabin all that heat and then some ends up in the engine bay blasting the front of the Quick Fuel bowl.

Rant 3

I replaced the fuel supply (originally 3/8"), fuel return (originally 1/4") and vent lines (originally 5/16") with all 3/8" stainless and blew through each one checking them before I finished there were no obstructions for flow over that length of run that were out of normal.

Pictures might help.

Old intake and carb.

The intake is a '69/'70 LS5 intake, but there's not much runner length.

The old carb, whilst I could never get the idle mixture adjusted correctly did work extremely well till the end where the rubber bits died. It's been 20 years since this Q-jet was cracked open. 20 years alone is a good track record for never having to monkey with a carb.

Now this carb would lose its fuel in its bowl if you let the car sit for more than 15 minutes. But with a tiny bowl and situated right in the chilled part of the carburetor it didn't take long for the large fuel pump to fill whilst cranking and even on hot days the fuel in the carb stayed cooled and never had a problem with heat even on hot days with the air con blasting away.

Worse comes to worse I could always freshen up the Q-junk with new rubber bits and see if it with an adapter will fit under the hood in lieu of the Holley/QuickFuel thing. 3 steps forward, 10 backwards.

Brand new high rise, air gap, dual plane aluminum intake QuickFuel 750.

I installed the fuel filter down low to keep as cool as possible.

I mean I'm happy with the way it looks, but other than driving in a cooler evening in which it runs fantastic, it runs like do-do in hot weather.

I don't have a carb spacer on it. The cooling system works really well and it's quite large at holding 24 quarts of coolant. The thermostat is 160˚, the engine rarely goes over 170˚ in the heat of the day with air con on max.

I could probably get away with a 1/4" spacer under the carb. It has a decently thick gasket under it now, but it's already on an air gap high rise intake.

I did want to go immediately to fuel injection, but I cannot find an intake that's air gap, dual plane, oval port with multiport injection bosses on it.

This is the closest intake I could find but it's rectangular port and not oval. But otherwise this is exactly what I'm looking for. Seeing as how our Panthers run on this easy to boil fuel as well as our '96 Impy with no noticeable problems fuel injection for the old cars is just the way to go, well up here anyway.

Also they have discontinued the BBC fuel pump with return. No more, I must have bought one of the last ones from Rock Auto last year. The best you can do is some aftermarket generic thing with an inlet and one outlet.

All good reasons to make the switch to fuel injection.

As a side note, I had recently talked to a friend up here who has an automotive repair service and he basically said customers who have carburetor cars have nothing but trouble and he will not build any old car with a carburetor anymore. He had one customer keep coming back with an 80's Ford with an Autolite and he had to remove the air horn off the car, run the car and show the customer the fuel percolating right in the bowl of the car. Basically it's the fuel and there's really nothing you can do about it.

Now 20 miles away they do sell ethanol free fuel, but, it's as expensive as AVGas last time I checked on it. I have an AVGas pump close to the house. As long as you do not have a catalytic converter or O2 sensor I'd rather run leaded 100 octane AVGas.

However being constrained to two fuel stations would be extremely poor planning on my part. I'm just a little frustrated.

I did check the Q-jet bottom plugs and they are clean, no sign of leaks, which is rather astonishing as I knew about this problem affecting Q-jets a long time ago. The plug on the outside of the carb has a slow leak as evidenced by a stain.

I will say this for ethanol fuel, I ran the cheap stuff in the convertible for decades and that bowl was clean as a whistle. If I could only figure out the strange idle mixture problem its always had I really would be considering refreshing it and putting it back on with a spread bore adapter and hoping it all fits under the hood. I mean I really don't want to, but the Holley style carb isn't working out. Then again winter is around the corner and the cooler weather will in effect buy me some time, perhaps till I figure out a multi-port fuel injection system.

The fuel in the Q-jet obviously would boil away shortly after the engine was shut down due to the proximity of the large cast iron heat stove it was bolted directly to with nothing but a gasket and having a tiny bowl of fuel to begin with.

About the Kinsler injection. I had a look see at their website, it appears they only do IR intake setups. But I shall drop them a line to see if they have what I'm looking for as it doesn't hurt.

But first here's the premise I'm basing this question on: on late 60's and early to mid 70's at least, GM had fuel pumps with a return line on big block cars equipped with factory air or if you were lucky enough to special order a big block that would spin the tyres on something other than wet leaves.

My '73 Caprice Classic convertible with 454, although in factory form would struggle to spin the tyres on wet leaves did come with factory air con and has a rather large fuel pump with return. As a result it does not suffer from suction side vapor lock because of the constant cooler fuel flow to the pump. Did any Fords have this? I know none of our 3rd gen full size Fords had this option either with big blocks and factory air.

Now in some cases where the fuel is either percolating in the carb fuel bowl or outright boiling none of this helps.

Cheers.

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