Another Timing question! 340 based 416 Stroker - Is my vacuum advance improper?

[72 Challenger]

Hi Everyone,

I bought the "read your spark plugs" guide and noticed that my timing mark on my ground strap is way over at the main body of the plug. In the guide it basically speaks to fixing the known issues first. I picked up myself a fancy timing gun and came out with these numbers:

Vac. advance disconnected:

Idle set to 800RPM
Initial: 8 BTDC
Full mechanical advance at 2500: 24.4 BTDC (this seems low?)

Vac. Advance connected:

Idle set to 800RPM
Initial 23.4
Over 2500 RPM: 44.4

The decision to look at timing is because even with a new thermostat, a rad flush, new rad hoses w/spring, she still climbs in temp, especially on the highway and the plugs say too advanced in the timing dept. Even with the low compression and the 94 she will still ping a touch under full throttle. Taking into account that this motor is in a 1970 Plymouth Duster it only has a 22" Rad. The engine is 10.1:1 compression, 340 based 416 stroker, for fuel I run 94. Rear gear is 3.55 SG. A833 4 speed. Thermostat is a 160 degree unit and opens (had a 180 before).

Should my vacuum advance be pulling that much timing at idle? I thought it was not supposed to be pulling timing at idle? Does the vac advance pull too much timing for cruising on the highway at 44 degrees causing a lean/ hot scenario? I thought ideal was somewhere around 32 degrees. I am running an Edelbrock Thunder AVS carb with the vacuum connected to the port on the front of the bottom plate of the carb, on the drivers side.

Ideas? ideally i'd like to keep the vac advance because the car is pretty much a show car, looks just like she left the factory.

[DeathProofCuda]

If you are running your vacuum advance off the ported vacuum connection on your carb and your vacuum advance is advancing the timing at idle, it means you have the throttle blades on your carb adjusted too far open.  Turn down your idle screw adjustment to close the throttle blades, and then bump up your idle speed by advancing your initial timing (without the vacuum advance connected).  If the throttle blades are set correctly, when you reconnect the vacuum advance your timing and idle speed should not change.

Another possibility is that you are running your vacuum advance off the port on the carb that is always under manifold vacuum, which would always engage the vacuum advance.  Some folks prefer to tune that way, but I'll try not to start the endless debate of ported vs. manifold vacuum.

[72 Challenger]

If your vacuum advance is advancing the timing at idle, it means you have the throttle blades on your carb adjusted too far open.  Turn down your idle screw adjustment to close the throttle blades, and then bump up your idle speed by advancing your initial timing (without the vacuum advance connected).  If the throttle blades are set correctly, when you reconnect the vacuum advance your timing and idle speed should not change.

This sounds very logical, I will verify this. I'd expect that my initial should be above 10 degrees at least.

[DeathProofCuda]

@72 Challenger , check out my modified post above.  I initially forgot to mention the possibility that you have your vacuum advance connected to the port of your carb that is always under manifold vacuum.  Trying to rush through too many things this morning and not doing any of them well.

I'm not familiar with that Edelbrock carb, but maybe someone else will chime in, or you can look into it a bit more to confirm whether you are running off a manifold or ported vacuum connection.  Good luck.

[72 Challenger]

@72 Challenger , check out my modified post above.  I initially forgot to mention the possibility that you have your vacuum advance connected to the port of your carb that is always under manifold vacuum.  Trying to rush through too many things this morning and not doing any of them well.

I'm not familiar with that Edelbrock carb, but maybe someone else will chime in, or you can look into it a bit more to confirm whether you are running off a manifold or ported vacuum connection.  Good luck.

Thanks for tagging me I only noticed your update when I got the e-mail. I will look into it. ON the manual for the carb it lists the ports as "for non emissions controlled vehicles and for emissions controlled vehicles. I put mine to the "not" side, which is the drivers side but I am open to being wrong.

[DeathProofCuda]

Yeah, the port for non-emission controlled vehicles is probably always under full manifold vacuum.  The ported vs. manifold vacuum and the vacuum advance vs. no vacuum advance debates are endless.  IMHO, neither choice is wrong.  You just need to decide which option is best for you and then tune accordingly.

[72 Challenger]

 I won't open that can of worms. I am more familiar with the ported way so, I am going to stick with that. I will switch the line and see what happens.

[7212Mopar]

I kind of recall CP mentioned that the vacuum pot can be adjusted with a small allen key or screw driver.

[Skdmark]

I kind of recall CP mentioned that the vacuum pot can be adjusted with a small allen key or screw driver.

Correct. If your vacuum advance has the hex shaped end by the vacuum port then you can insert an allen key into the port of the vacuum advance and adjust it. CCW increases vacuum.

Nice write up I had bookmarked on vacuum advance adjustments.
https://www.forabodiesonly.com/mopar/ams/how-to-limit-and-adjust-chrysler-vacuum-advance-cans.183/

[71383bee]

I prefer to set for total first and adjust from there.  WITHOUT the vac advance connected and ports plugged rev the motor up till no longer advancing (around 3k).  Set the car for 34 to 36 advance.  Back off the throttle and see where initial is at.  IF its between 15-18 your in pretty good shape.  if too low it needs to be recurved.  Connect the advance to the ported side and check for total again and see where it is at.  if it pings while doing this then you can back out the advance by using a  (i think) 5/32" allen wrench through the VA port. 

From the settings you posted above it looks like your set too low and relying on the vacuum advance hooked to manifold as a crutch for initial.  On heavy throttle the VA will not pull timing and the motor will fall off in power.  under idle and light throttle it probably runs great! 

[autoxcuda]

My 416 has 9.7:1 measured compression with Edelbrock heads and I run 91 octane.

I run 32 degrees total advance without vacuum advance. If forgot my initial and curve setting. It's a MSD E-curve distributor.  But IIRC initial is over 10 degrees.

[Chryco Psycho]

Virtually every engine I tune I leave the vacuum advance off or I stick a ball brg inside the hose so it looks correct but will not function generally the timing curve is too long . I don't use a light at all , I bring the engine up to around 2500-2800 & advance timing just until rpm quits rising & leave the timing on the cusp where it rises , any more advance & the RPM will not rise , if it pings yu either need better fuel or you can back off the timing a little . After setting the timing at 2500 rpm return it to idle if advancing the timing at idle from the same setting increases  rpm the curve is too long , if retarding increases idle the curve is too short .
Total timing at RPM is the most critical as that is where the engine spend the majority of the time .
Yes you can adjust the vacuum advance setting with a small allen key as mentioned above , there is about 14 turns available inside going from zero to about 14* advance , CCW reduces the advance available .

[7212Mopar]

Or do EFI with computer controlling the timing. Easy to adjust and make changes.

[72 Challenger]

While I go and frig around with this, here are the specs on my motor.

Anyone want to comment on WTF they would do for settings? Is this a big cam that needs a ton of initial?

I'm extremely frustrated. Part of me says shell out big money for a restoration rad with higher cooling capacity but I'm not sure that's going to solve the issue.

I'm off to go and play with it some more.

Back in a bit. I have always struggled with tuning and spark plugs and air fuel. I never know what setting to touch until I have completely screwed it up.

[7212Mopar]

Are you saying you have high engine temperature issues? You say engine look stock so I assume you are running mechanical fan and cast iron heads. Eight degrees initial seems low but timing should not advance that much at idle with vacuum advance connected and 44 degrees at 2500 seems too much. What is the timing at 3500? I would say your 112 degree cam and lift is not too big for a stroker motor.

My 416 is 9.9 CR but running aluminum heads, Comp Cam CRS XR292-HR-10 and 1.6 rocker. My engine builder set mine at 34 degrees at 3200 ruining a 750 Quickfuel carb. He specifically wrote on the build sheet telling me not to hook up vacuum advance. I since had converted to EFI with computer timing control. It is now set at 12 degree initial and 32 degree total. I am running mechanical fan and a brass OEM replacement radiator. Engine temp will get up to 200F on a hot day in stop and go traffic. Mechanical fan don't move enough air at idle stop and go traffic. I solve this by removing the rallye hood insert to let air out from under the hood.

I think you should at least try what CP suggested and disconnect vacuum advance and plug it to see how the engine runs. Have you try adjusting the vacuum advance pot?