440 issue after swapping to aluminum heads, need advice

[Cheapsunglasses]

Thanks for sharing the solution. The distributor that I am running does not have a vacuum advance. I guess you don't need one. Just my opinion.

Someone smarter will chime in, but I’ve had cars with them and without that run fine. People say it’s to help fuel mileage and drivability.

My first car was a 68 satellite 4 door, I put a 66 hp 383 in it, and a mechanical Mallory unilite, never had issues with running it, if I remember right with 3.55s and no overdrive I got 12-13mpg. The great thing about unilites they wire up just like the points, so conversions from points are easy, but who cares about that, they have a cool sticker lol

 

[Nxcoupe]

I can not stress this enough, I do not have a vacuum leak! Not in the intake, not in the carb. Thanks for the help, but please stop with the vacuum leaks, lol.

As soon as I took the avs off and put a different carb on everything was fine with the AFR. I have a 440 afb on it, it might be a little rich at rpm, but that can be taken care of with a little carb work. That’s over with.

Now I’m dealing with the distributor. Plugged to ported vacuum I can’t rev past 3k rpm without it cutting out. Disconnect it and problem gone. So now I need to dig into that

Thanks again for the advice!

Dist shaft and plate are worn, or you have the dist way to advanced. If it is an old dist, it is worn out and what happens is as the vacuum pulls on the plate to rotate it, the pick up looses signal. Just a guess but I've had this happen myself. New dist fixed the issue.

 

[Geoff 2]

MF,
post #70 is still incorrect in part. If you want to say PVA works off venturi vacuum, then so does MVA. The PVA port is in the throttle bore, below the venturi. The MVA port is also in the t/bore but lower. Once off idle, when the PVA port is uncovered, the vacuum available to PVA & MVA are exactly the same. Something that does work on vent vac is a the secondaries on a Holley vac sec carb, where the port is located in the venturi.

 

[Geoff 2]

There is so much misinformation around about PVA & MVA. We got PVA because of emissions, not because it is better than MVA [ it isn't ].

Hot rodders used to & some still do lock their dists. So if the engine likes 36* @ WOT, it has 36* at idle......& everywhere else. No VA advance is likely to be needed, but in some cases, a few extra degrees might help economy & keep the engine cooler. Using MVA will add timing at idle which might benefit the combo. If the combo is pretty mild, & doesn't need more idle timing, then PVA might be good. Rarely is PVA going to be better than MVA in any engine.
The problem with locked dist is detonation & hard starting. There is where MVA comes to the rescue! Because VA is load sensitive [ & not rpm sensitive like the centri curve ], timing drops away under load. More cam timing & lower CR requires more idle timing. By using MVA to add timing at idle, you get a smoother running, cooler & more efficient engine at idle. Of course you can add too much. When I hear comments such as 'MVA didn't work for me', it is either [1] too much timing added [2] a non-adj VA unit used with low vac cam [3] or lean mixture...or all three. The problem is/was not MVA, the problem was how it was tuned/added to the ign.
A quote from D. Vizard about idle timing; it is in a carb book, not an ign book. You might want to ponder why...
'The optimum IDLE advance is typically about 35-40* for a short cammed street engine & [ though not commonly realized ] as much as 50* for a street/strip engine'.

My engine idles with 48*.

 

[Moparfever65]

MF,
post #70 is still incorrect in part. If you want to say PVA works off venturi vacuum, then so does MVA. The PVA port is in the throttle bore, below the venturi. The MVA port is also in the t/bore but lower. Once off idle, when the PVA port is uncovered, the vacuum available to PVA & MVA are exactly the same. Something that does work on vent vac is a the secondaries on a Holley vac sec carb, where the port is located in the venturi.

Incorrect. I even pulled out a Holley and blew compressed air through the ports to ensure what I believed was true. The manifold vacuum port comes out the bottom of the baseplate, the ported vacuum comes out in the venturi. BTW, when I say the ported vacuum is a venturi vacuum, I didn't mean that because it's in the venturi, but the vacuum is pulled as a result of the high speed airflow moving across the port (venturi effect). That's why the vacuum increases as the airflow increases. That's also why you get too much advance when it's hooked up to the vacuum advance diaphragm when the engine hits 3k. Manifold vacuum is created by the engine trying to pull air past the partially closed butterflies.

 

[Geoff 2]

You must have been blowing through the wrong port, because the PVA port does NOT exit into the venturi, it exits into the bore, below the venturi. Same as the EGR port. I do not know how to post pics, maybe somebody can?
[1] Original Holley book by M. Urich, p.130, pic of the 4412 2 bbl carb CLEARLY shows the PVA port in the base plate [ throttle bore ], not venturi.
[2] D. Vizard Holley book SA 216, p. 30. Clear pic of PVA port in the base plate with description of how it works.
[3] Doug Roe QJ book, p. 46. Clear pic of PVA port in the bore, WELL below the venturi.
[4] QJ, 4150/60 Holleys & TQ carbs have separate base plates to the main body. The BPs contain the t/blades & shafts & are parallel bored to the bore size; the PVA port exits the bore in the BP. The venturiis are NOT in the BP.
[5] Your last 3 lines are a lot of nonsense. What controls the amount of VA that is added is dependant on many factors & not necessarily related to an exact engine speed [ 3k ].

 

[Moparfever65]

You must have been blowing through the wrong port, because the PVA port does NOT exit into the venturi, it exits into the bore, below the venturi. Same as the EGR port. I do not know how to post pics, maybe somebody can?
[1] Original Holley book by M. Urich, p.130, pic of the 4412 2 bbl carb CLEARLY shows the PVA port in the base plate [ throttle bore ], not venturi.
[2] D. Vizard Holley book SA 216, p. 30. Clear pic of PVA port in the base plate with description of how it works.
[3] Doug Roe QJ book, p. 46. Clear pic of PVA port in the bore, WELL below the venturi.
[4] QJ, 4150/60 Holleys & TQ carbs have separate base plates to the main body. The BPs contain the t/blades & shafts & are parallel bored to the bore size; the PVA port exits the bore in the BP. The venturiis are NOT in the BP.
[5] Your last 3 lines are a lot of nonsense. What controls the amount of VA that is added is dependant on many factors & not necessarily related to an exact engine speed [ 3k ].

Sorry, I meant in the bore. It works on the venturi principle like I said, same as the transfer ports. The manifold vacuum does begin through the bottom of the baseplate, therefore no venturi effect. Just hook up a vacuum gauge to each port and see for yourself. 3k is where he's seeing his problem. It always happens somewhere around cruising rpms in my experience.

 

[Splangj]

In post 46 you say after you plugged the vacuum advance it ran fine. That tells you the distributor itself is fine. If you slowly rev the engine with the VA connected, it’s going to add a LOT of advance, which could make the engine crap out. you need to make the engine run fine with no VA first, then connect it to ported vacuum. if it starts pinging or crapping out, you can hopefully close the VA diaphragm some by inserting a small Allen wrench into the hose nipple and turning it clockwise I believe. Put a hose on the VA and suck on it, while watching how much travel the diaphragm arm moves in. You will want to shorten the travel up quite a bit it sounds like. If you connect the VA to manifold vacuum, it will start advancing timing as soon as it starts, leading to erratic timing and the idle speed will start to increase, making it hunt around for a sweet spot. Vacuum advance is only for economy, possibly cooler running and longer ring life due to better combustion. My 496 distributor has no VA provisions and runs well, even though I would welcome trying one with it. If the engine will only run well without the VA after tuning it’s range, so be it. You MUST have the mechanical advance dialed in before adding VA or any other tuning for that matter.

 

[Nxcoupe]

In post 46 you say after you plugged the vacuum advance it ran fine. That tells you the distributor itself is fine. If you slowly rev the engine with the VA connected, it’s going to add a LOT of advance, which could make the engine crap out. you need to make the engine run fine with no VA first, then connect it to ported vacuum. if it starts pinging or crapping out, you can hopefully close the VA diaphragm some by inserting a small Allen wrench into the hose nipple and turning it clockwise I believe. Put a hose on the VA and suck on it, while watching how much travel the diaphragm arm moves in. You will want to shorten the travel up quite a bit it sounds like. If you connect the VA to manifold vacuum, it will start advancing timing as soon as it starts, leading to erratic timing and the idle speed will start to increase, making it hunt around for a sweet spot. Vacuum advance is only for economy, possibly cooler running and longer ring life due to better combustion. My 496 distributor has no VA provisions and runs well, even though I would welcome trying one with it. If the engine will only run well without the VA after tuning it’s range, so be it. You MUST have the mechanical advance dialed in before adding VA or any other tuning for that matter.

OR, the dist is worn out and as the vac adv moves the plate, it lets the reluctor hit the pickup and shuts the car off.
If manifold vacuum worked better for vacuum advance then every vehicle that came out of detroit would have it that way. It's designed to add advance during accell and during cruise. Most modern vehicles(and the old ones) used well over 40 deg advance at cruise and light accell. I've seen upwards of 50 deg in certain vehicle spark tables. If he can't set the total timing further discussion is a waste of time and a great exercise in high school debate.
OP, with engine idling, pull vacuum on the vac diaphragm, if it dies, you prob have a dist issue. You can also remove dist cap and pull vacuum on it as you watch the pick up plate move and watch the gap between pick up and reluctor, if it changes, there's your issue. If it was too much advance, it wouldn't just shut off. Jmho.

 

[Cheapsunglasses]

OR, the dist is worn out and as the vac adv moves the plate, it lets the reluctor hit the pickup and shuts the car off.
If manifold vacuum worked better for vacuum advance then every vehicle that came out of detroit would have it that way. It's designed to add advance during accell and during cruise. Most modern vehicles(and the old ones) used well over 40 deg advance at cruise and light accell. I've seen upwards of 50 deg in certain vehicle spark tables. If he can't set the total timing further discussion is a waste of time and a great exercise in high school debate.
OP, with engine idling, pull vacuum on the vac diaphragm, if it dies, you prob have a dist issue. You can also remove dist cap and pull vacuum on it as you watch the pick up plate move and watch the gap between pick up and reluctor, if it changes, there's your issue. If it was too much advance, it wouldn't just shut off. Jmho.

If I’m being honest this whole vacuum advance stuff has turned this thread into a high school debate!

 

[Splangj]

OR, the dist is worn out and as the vac adv moves the plate, it lets the reluctor hit the pickup and shuts the car off.
If manifold vacuum worked better for vacuum advance then every vehicle that came out of detroit would have it that way. It's designed to add advance during accell and during cruise. Most modern vehicles(and the old ones) used well over 40 deg advance at cruise and light accell. I've seen upwards of 50 deg in certain vehicle spark tables. If he can't set the total timing further discussion is a waste of time and a great exercise in high school debate.
OP, with engine idling, pull vacuum on the vac diaphragm, if it dies, you prob have a dist issue. You can also remove dist cap and pull vacuum on it as you watch the pick up plate move and watch the gap between pick up and reluctor, if it changes, there's your issue. If it was too much advance, it wouldn't just shut off. Jmho.

Good advice to see how much slop is on the VA advance plate. Pretty sure that Mallory is the Unilite. It has a module and small slots in the lower half of the rotor. It works off light, not a magnetic pulse. However if the plate was sloppy, that could give some real problems. I’m with you on ported vacuum being used, as I did state

 

[Nxcoupe]

Good advice to see how much slop is on the VA advance plate. Pretty sure that Mallory is the Unilite. It has a module and small slots in the lower half of the rotor. It works off light, not a magnetic pulse. However if the plate was sloppy, that could give some real problems. I’m with you on ported vacuum being used, as I did state

But I'm pretty sure the plate still moves and if there is wear, it will still shut it down. But duly noted.

 

[Cheapsunglasses]

Good advice to see how much slop is on the VA advance plate. Pretty sure that Mallory is the Unilite. It has a module and small slots in the lower half of the rotor. It works off light, not a magnetic pulse. However if the plate was sloppy, that could give some real problems. I’m with you on ported vacuum being used, as I did state

Yes it’s a unilite, and it has a module with a light

 

[Geoff 2]

Nxcoupe, post #89.

Actually every car out of Detroit DID use MVA. In the mid to late 70s. And while GM doesn't represent 'every vehicle', it represents a HUGE number & many if not all GM divisions used MVA until around 1968, when emissions forced the USELESS PVA on us. Mopar missed the boat on MVA, plain & simple. My 1966 GTO left the showroom idling @ 26*: 6* init + 20* added with MVA. Lots of idle timing makes the engine more efficient; it makes more HP using less fuel. With the switch to PVA & high operating temps for emissions, engines could overheat. The Detroit fix [ M included ] was to have a temp sw that switched from PVA to MVA. That increased idle speed, which turned the w/pump & fan faster & reduced temps.

 

[Geoff 2]

Sunglasses, I would try a different dist. Unilite were not called Unidark for nothing...

 

[Cheapsunglasses]

Sunglasses, I would try a different dist. Unilite were not called Unidark for nothing...

I’ll take my “unidark” over Multi **** Discharge any day

 

[Geoff 2]

Who said anything about multi discharge? Back in the day, Uni modules were one of the fastest selling items at speed shops.....

 

[Cheapsunglasses]

I’m not sure if anyone is still interested in this, I needed a couple parts, which took time, but I’ll give an update for those who are.

I’m using the 67 440 afb, I tried running it with ported and direct vacuum, both ways leaned the carb out, which means som ting wong. So I ran it no vacuum advance, 10:1 rich, and the exhaust note wasn’t smooth sounding, it was kinda bubbly for lack of better terms, and when I let off the exhaust it sounded like a Detroit Saturday night, all kinds of popping and banging.

So like I’ve mentioned before I’m using parts I have laying around before buying anything, I have a dual point Mallory with mechanical advance, I accidentally bought thinking it was electronic, so it’s my backup side of the road dizzy. I put it in, got it timed, 10 degrees before tdc per mopars instructions. It ran rich still, but the exhaust note was a lot cleaner sounding, and it ran better then it’s ever ran. I’ve never gotten it to almost break the tires loose going 30mph and stabbing the throttle.

So I guess I’m on the right track.

 

[RemCharger]

I’m not sure if anyone is still interested in this, I needed a couple parts, which took time, but I’ll give an update for those who are.

I’m using the 67 440 afb, I tried running it with ported and direct vacuum, both ways leaned the carb out, which means som ting wong. So I ran it no vacuum advance, 10:1 rich, and the exhaust note wasn’t smooth sounding, it was kinda bubbly for lack of better terms, and when I let off the exhaust it sounded like a Detroit Saturday night, all kinds of popping and banging.

So like I’ve mentioned before I’m using parts I have laying around before buying anything, I have a dual point Mallory with mechanical advance, I accidentally bought thinking it was electronic, so it’s my backup side of the road dizzy. I put it in, got it timed, 10 degrees before tdc per mopars instructions. It ran rich still, but the exhaust note was a lot cleaner sounding, and it ran better then it’s ever ran. I’ve never gotten it to almost break the tires loose going 30mph and stabbing the throttle.

So I guess I’m on the right track.

Crank up the timing and see what it does.

 

[Cheapsunglasses]

So obviously there’s a problem with the electronic unilite, I’ll run the points until I can buy a new distributor. But I think the biggest questions I still have is do I completely forget about the 4966s carb, r413 mentioned it being an leaner carb, and it makes sense being a smog year carb. Or does it?

And do I attempt tuning with distributors, or carburetors with the offy intake? Intakes aren’t cheap, but if I have to then it is what it is.

I don’t care about cost anymore, I just want to get this car back on the road, nothing is more fun then a big block and a 4 speed!