Vacuum advance question / issue

[WhiteGP]

Whenever I hook up my vacuum advance to ported vacuum, my 440 runs like CRAP, very rough, unhook ( mechanical only ) and it runs great

I have verified the distributor is holding vacuum, and with the engine running and a vacuum pump on the distributor the engine will advance smoothly for a second then get very rough when vacuum applied. Any thoughts out there, this is a stock 440. I do have a new electronic system i guess i need to install sooner than later but curious if anyone has some input

Thanks

 

[Deathproofcuda]

Seems odd, as most engines respond positively to a little more advance, but can't really tell without more information. What is your base timing set at and how is it changing in response to these changes? What is rpm doing when you make these changes? How does timing change in response to rpm changes? (need this to understand if your mechanical advance is working correctly)

Do you have a timing light? What kind of vacuum do you have at idle?

 

[Chryco Psycho]

I generally disconnect vacuum advance or stuff a ball brg in the hose so it looks like it is connected , just tweak the mech advance to get the best results

 

[Bret Schneider]

I second the need to check and make sure the mechanical advance is working correctly. I've seen the mechanical advance stuck in the advanced position, generally from a little corrosion after an extended period of not moving, as in following winter storage. Setting the base timing with the mech advance stuck open results in the primary side of the ignition (pickup coil/reluctor) being out of synch with the secondary side of the ignition. (cap/rotor). In this condition, advancing the primary side via the vacuum advance can really mess with the timing.

 

[moparleo]

What carburetor are you using ? And a picture of your setup always helps so we can see what you see.


https://www.hotrod.com/articles/quick-tech-still-need-vacuum-advance/

 

[WhiteGP]

I generally disconnect vacuum advance or stuff a ball brg in the hose so it looks like it is connected , just tweak the mech advance to get the best results

Yea, I have vacuum plugs on both sides, I have been playing with timing and the car runs perfect at the 5-7 degree BTC. But at this setting of course its a bit harder to start when warm sometimes.

The Mechanical advance IS working, I just got an itch yesterday to take a closer look at the unhooked vacuum system and why its not acting right, my previous 440 ran fine with it? I'm going to just give up and run no vacuum, it really is running great without...

Thanks Psycho !

 

[WhiteGP]

What carburetor are you using ? And a picture of your setup always helps so we can see what you see.


https://www.hotrod.com/articles/quick-tech-still-need-vacuum-advance/

Hi Leo, I'm runnning an Edelebrock 1913 ( which I just put on ) i had a 1905 AVS2 before, same results. I'm going to not run vacuum per Psscho's comments

Thanks !!!

 

[WhiteGP]

I second the need to check and make sure the mechanical advance is working correctly. I've seen the mechanical advance stuck in the advanced position, generally from a little corrosion after an extended period of not moving, as in following winter storage. Setting the base timing with the mech advance stuck open results in the primary side of the ignition (pickup coil/reluctor) being out of synch with the secondary side of the ignition. (cap/rotor). In this condition, advancing the primary side via the vacuum advance can really mess with the timing.

This is interesting, I'm 100% sure the mechanical is working. I'm going to put the new Electronic in soon so I can control the curve and put an end to the madness

Thanks Bret

 

[WhiteGP]

Seems odd, as most engines respond positively to a little more advance, but can't really tell without more information. What is your base timing set at and how is it changing in response to these changes? What is rpm doing when you make these changes? How does timing change in response to rpm changes? (need this to understand if your mechanical advance is working correctly)

Do you have a timing light? What kind of vacuum do you have at idle?

Good Morning

Base timing is 5-7 RPMs are 750-780 Mechanical IS working, Per Psycho I'm just going to continue running no vacuum

 

[Challenger RTA]

mechanical advance stuck in the advanced position

I have to 3rd the advance. I was have some issues. One the carb was running rich. The other was spark. They compounded each out. The dual point from factory had points and condenser over the years. Cap and rotor had corrosion. Drop in a electronic distributor. Ran a lot better. Need to take apart dual point and clean. I also can see it's not moving as it should. Never been cleaned since 11-70.

 

[Bret Schneider]

I must have missed the part about the points. I was thinking electronic ignition. Points are even more susceptible to causing problems like this. Even though the gap might be set correctly if the spark advance isn't working correctly the dwell time gets all messed up. If nothing else, bet the electronic ign system fixes the problem.

 

[Challenger RTA]

I must have missed the part about the points.

He didn't say points or electronic. You didn't miss anything. I was just making a point about maintenance. Might just fix everything. Sometimes you just have to go a little deeper.

 

[WhiteGP]

I have to 3rd the advance. I was have some issues. One the carb was running rich. The other was spark. They compounded each out. The dual point from factory had points and condenser over the years. Cap and rotor had corrosion. Drop in a electronic distributor. Ran a lot better. Need to take apart dual point and clean. I also can see it's not moving as it should. Never been cleaned since 11-70.

Thanks

this is a 70 U-Code Cuda, it has single points, my 6-pack had duals. This IS a NEW carb and could very well be running rich, I have not completely dialed it in yet ( once again, the cart before the horse ) I will say that Edelbrock 800 cfm 1913 AVS2 rocks, I just need to install the electronic, looking at the curve options now.

 

[Deathproofcuda]

Good Morning

Base timing is 5-7 RPMs are 750-780 Mechanical IS working, Per Psycho I'm just going to continue running no vacuu

Seems even more odd. Base timing of 5-7 degrees is pretty low. Most engines want more than 10, many are happiest closer to or even over 20 degrees of initial timing. That fact that yours runs like crap by adding vacuum advance to 5-7 degrees of base timing is strange. Something else is going on here...

 

[WhiteGP]

Seems even more odd. Base timing of 5-7 degrees is pretty low. Most engines want more than 10, many are happiest closer to or even over 20 degrees of initial timing. That fact that yours runs like crap by adding vacuum advance to 5-7 degrees of base timing is strange. Something else is going on here...

Yea, something is odd, I was running 12 and it runs OK, but much more power at 5-7, it did want to heat up a bit so I may need to bump it back up, This is to the best of my knowledge a stock 1970-440 ( oh i wish i knew whats really in the engine, cam etc )

I saw this below in bold and it truly does run great... after i set to 5-7 i thought i would to add the vacuum, which started all of this, BUT this below is wrong for my four barrel, a different search says 8 degrees factory. In all honesty this car is mostly for cruising thru town on a weekend and the occasional show. My "peddle to the floor and shift" days are over.

• Idle Timing: 6-8 degrees BTDC
• Total Timing: Typically around 32-36 degrees BTDC

This is where I got the 5, it should be 7-8 or a bit more, I'm just going to run 8-10 until i get new gear in with a working vacuum that will get me to 35 ( the mechanical stops at 25 in my new rig ) Thanks to Everyone, I appreciate the input !

"The following are the 440 Six Pack or 6-BBL timing specs for each year. 1970: 5° BTC (manual or auto) plus or minus 2 1/2°. Set at curb idle (with C.A.S.) 1971: 5° BTC (manual or auto) plus or minus 2 1/2°. Set at curb idle (with C.A.S.) 1972: 2.5° BTC (manual or auto) plus or minus 2 1/2°."

 

[Deathproofcuda]

Yea, something is odd, I was running 12 and it runs OK, but much more power at 5-7, it did want to heat up a bit so I may need to bump it back up, This is to the best of my knowledge a stock 1970-440 ( oh i wish i knew whats really in the engine, cam etc )

I saw this below in bold and it truly does run great... after i set to 5-7 i thought i would to add the vacuum, which started all of this, BUT this below is wrong for my four barrel, a different search says 8 degrees factory. In all honesty this car is mostly for cruising thru town on a weekend and the occasional show. My "peddle to the floor and shift" days are over.

• Idle Timing: 6-8 degrees BTDC
• Total Timing: Typically around 32-36 degrees BTDC

This is where I got the 5, it should be 7-8 or a bit more, I'm just going to run 8-10 until i get new gear in with a working vacuum that will get me to 35 ( the mechanical stops at 25 in my new rig ) Thanks to Everyone, I appreciate the input !

"The following are the 440 Six Pack or 6-BBL timing specs for each year. 1970: 5° BTC (manual or auto) plus or minus 2 1/2°. Set at curb idle (with C.A.S.) 1971: 5° BTC (manual or auto) plus or minus 2 1/2°. Set at curb idle (with C.A.S.) 1972: 2.5° BTC (manual or auto) plus or minus 2 1/2°."

Keep in mind that factory timing specs from that time were also based on emissions controls and in some cases were based on Chrysler's use of distributors with advance retard mechanisms. You might use them as a starting point, but I'd never use them as the basis for how my car is tuned now unless I wanted it to be a dog that runs too hot.

I would guess that most guys that have spent any time trying to tune their car for best performance are probably running base timing of 15+ degrees. There are endless Youtube videos on performance tuning and distributor mods for old Mopars. Standard recipe is more initial advance, lighter springs to bring the advance in faster, and then reducing the total amount of mechanical advance so that you don't exceed 34 to 38 degrees of total timing at WOT.

 

[moparleo]

I would use the vacuum advance. It is not a race car that only uses mechanical advance.
Every car forever used vacuum advance until the computer controlled ignitions.
Manufacturers have spent millions on r &d.
You only find mechanical advance only on off road vehicles.
The engine is running at all kinds of rpms sometimes under load, sometimes not.
Your choice.