440 issue after swapping to aluminum heads, need advice

Geoff 2

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When you run MVA or PVA, the carb can run lean, especially a production carb. It is a 'quirk' of VA. The extra timing from VA makes the engine more efficient & it requires less fuel to produce the same rpm. Using MVA as an example is easier to understand the concept: idle mixture comes from the idle port AND the partly exposed transfer slot; idle rpm increases when plugged into MVA. When idle rpm is reset to the original speed, less T slot is available for idle fuel & the mixture is leaner. The fix is often as simple as adjusting the mixture screws but sometimes the IFR needs to be enlarged slightly.
I haven't read the whole thread, but a bigger cam &/or lower CR require more idle fuel.
Congrats on using a great carb.

New dist. Simplest route is to buy the Chrys elec ign kit. Points belong in a model T....
 

Cheapsunglasses

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When you run MVA or PVA, the carb can run lean, especially a production carb. It is a 'quirk' of VA. The extra timing from VA makes the engine more efficient & it requires less fuel to produce the same rpm. Using MVA as an example is easier to understand the concept: idle mixture comes from the idle port AND the partly exposed transfer slot; idle rpm increases when plugged into MVA. When idle rpm is reset to the original speed, less T slot is available for idle fuel & the mixture is leaner. The fix is often as simple as adjusting the mixture screws but sometimes the IFR needs to be enlarged slightly.
I haven't read the whole thread, but a bigger cam &/or lower CR require more idle fuel.
Congrats on using a great carb.

New dist. Simplest route is to buy the Chrys elec ign kit. Points belong in a model T....
Great analogy!

Which one are you saying is a great carb, the afb, or the avs?

This issue I was having with the avs, it didn’t matter what metering rod/jet combo I put in it, it would always lean out 2-3 points, stay there for a few thousand rpm and shoot to straight rich

The afb keeps a good afr, until cruising, then it’s rich
 

i_taz

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If you end up changing intakes and go the spreadbore route like the Holley don't discount a thermoquad. I have 2 of them and there growing on me especially after living with a Eddy 1411... Your limited to how much you can tune them unless your willing to step up for a
kit on ebay but you may not have to do anything...
 

Cheapsunglasses

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If you end up changing intakes and go the spreadbore route like the Holley don't discount a thermoquad. I have 2 of them and there growing on me especially after living with a Eddy 1411... Your limited to how much you can tune them unless your willing to step up for a
kit on ebay but you may not have to do anything...
I have love thermoquads! The direct connection book from the 70s actually states the thermoquad is the best high performance carburetor.
:thumbsup:

I have about 15 tquads laying around I should have used, but I went ahead and bought a new edelbrock avs2 800 cfm carb, unfortunately it’s back ordered, maybe I’ll cancel the order and build a tquad
:rofl:
 

i_taz

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I was so disgusted with the Edelbrock I think I did it on spite ! I cobbled one together from a rebuilt that came with a car I bought. Looked brand new, perfect center section that leaked like a sieve. Even put it in a bucket of water and could never find where it was dripping from but it also had these cheezy idle mixtures screws that I never saw before that had really small heads on them so when turned in the spring end would dig into the screw and felt like it was cross threaded or something. They had very long needle sections too? Turns out at some point I must have cross threaded the drivers side and thought, oh well here's a base plate for the scrap heap but I tried normal needles off another carb and I didn't tempt fate by seating them all the way and was still able to set them up perfectly. It can sit for 2 weeks and it'll fire right up w/o touching the gas (it's summer) and even idles with the air on...!!!

There's a few sites out there that list which rods and jets came with which carb so you may have a few winners in your stash. Just look up the serial number and you'll find them...
 
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Geoff 2

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Cheap,

Both the Edel & TQs are great carbs. The TQ would be my pick for general performance work. Just buy a repair kit & rebuild it. Make sure you also get a new Air Valve dashpot; they are now 40+ yrs old, the rubber goes hard & can cause all sorts of hard to diagnose strange problems. Set the AV tension to 2 turns. No other carb makes the full throttle roar when those huge secs are at WOT.
 

Cheapsunglasses

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Cheap,

Both the Edel & TQs are great carbs. The TQ would be my pick for general performance work. Just buy a repair kit & rebuild it. Make sure you also get a new Air Valve dashpot; they are now 40+ yrs old, the rubber goes hard & can cause all sorts of hard to diagnose strange problems. Set the AV tension to 2 turns. No other carb makes the full throttle roar when those huge secs are at WOT.
Thanks! I have an edelbrock on the way. I know this is off topic, But I have a 78 Lil Red Express truck, it’s been in the family since new. My uncle and owned it before me, he took it to a mechanic. The guy pulled the original thermoquad off, trashed it, and put an edelbrock carb on it. I bought a thermoquad from a guy with a 79 LRE, and it was giving me all kinds of trouble. You might have helped me figure that out!

54C7D0AD-4FCB-4BB2-A996-B62BB96F00E2.jpeg
 

i_taz

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Admittedly I got lucky but there's not much to them really. They never got to the level
of complexity like the Q-jets did with 2 dashpots but the engineering was impressive.

I looked at the Thunder initially but bought a newer Demon instead and then thought
why not try the real deal. I was more interested in trying a spreadbore than anything
else hoping it would run cleaner and be more efficient since there the most modern.

I'm being a little unfair to the Edelbrock, I had other issues with a leaky intake pan causing oil
to get sucked into the heads that I had a hard time dealing with and still don't have the vacuum
I should but it always gave me a hard time starting especially when hot. It was my first
car with a carb in many, many yrs so that didn't help but the TQ runs like an OEM carb
should, if that makes sense. Starts easily, especially when hot, smooth performance.
A lot of details and quality goes into an original part that repop's can never match which
goes for everything...
 

Gunner1

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Great thread. Same issue with my car. PO bought a 76 440 out of a Motor Home. Had it rebuilt. Speed Pro tall flat tops. Small cam. Eddy RPM intake. 175 psi cranking pressures. And a small eddy 600 mileage carb. Pinged like crazy. Had a points dist that was gapped at 007. I dumped the points and condenser for a petronix bolt in. Got much better. Still way to much advance when driving. Plugged the Vac adv line. It got better but still had too high 44 advance with only 10 at idle and no Vac. Added a Holley 750 DP. Things got better. I'm now running at 0 degrees and 34 at 2400. My guess is the dist springs and weights need a rebuild. Im having a Isky 292 Mega cam installed along with a MSD 6al and billet non Vac dist installed in a couple of weeks. I think this will settle things down untill I save up for some Trick Flows.
 

Road Grabber

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This is very much like an issue I had with an intake gasket leak. I could not find it spraying around the intake because it was underneath. I only discovered it when I removed the intake and could also see where oil was entering the bottom edges of the ports. I believe I had too many gaskets on cause I used paper with the bath tub.
I also had to track down a problem with percolation caused by the exhaust heat riser leaking heat right towards the fuel line. The combination of the two caused high rpm bucking and surging. Lose of power.

Another thing worth mentioning Is that my friend had a similar issue when his brake booster diaphragm was leaking. Block your intake vacuum fitting and see if you detect a difference. Check vacuum lines for tight seal if you have anything using manifold vacuum to function things.

Good luck.
 

BSB67

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This is very much like an issue I had with an intake gasket leak. I could not find it spraying around the intake because it was underneath. I only discovered it when I removed the intake and could also see where oil was entering the bottom edges of the ports.
This.

It is very likely you will miss identifying a vacuum leak problem by spraying stuff to find it.
 

Cheapsunglasses

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Ok, thank you everyone who has responded, and offered helped. For anyone else that sees this thread and wants to help, I’ve fixed it.

Bad vacuum advance. A couple of members suggested plugging it, I did and significant improvement. I pulled it out, and dropped in my backup Mallory dual point mechanical advance distributor, all the problems went away. So anyone else having a similar problem, check your vacuum advance.
 

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