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Vacuum advance does not affect the "haul *** quotient", correct?

Kern Dog said:
That 284 cam is sort of an oddball. It should make more power than the 280/474 and less than the 509 but my experience was that it idled as bad as the 509 with less power.
The 284 and 292/509 really like lots of initial timing. I ran 17 initial and 31 total (Instead of a more common 35 degrees) because at almost 11 to 1 it wanted to rattle at anything over half throttle. The MP distributor has an adjustable plate to widen or narrow the advance range. It is possible to run it tighter than I did if needed.
The Edelbrock is not the easiest to tune as compared to Holleys or the Holley based Demon/Proform, etc carbs.
As stated, vacuum advance should be only in effect at part throttle. If the vacuum line is connected to manifold vacuum, it puts the vacuum advance in from idle on up. That is not the correct use of the vacuum advance and will contribute to an unstable idle, especially with a lumpy camshaft. Think about it...The engine is running with loads of timing at idle, you lean on the gas a bit then floor it and half of the timing backs off. That is not going to give the best performance. It is better to set the initial and total advance THEN use the vacuum advance (Connected to a PORTED source) to improve mileage.
Click to expand...
Thanks for checking in, KD. Always a pleasure.
This one actually runs really nice at idle and smoothly all the way up through the RPMS - I've got some videos up on YouTube of it under this same name if you'd like to see it in action.
As stated before, I have the vacuum disconnected at the moment, figured I'd do that tweaking after I had the carb dialed in and such since it doesn't matter on much except part-throttle fuel economy.
Yes, I agree it should be connected to ported vacuum, as the FSM states.
The FSM also gives a procedure on how to adjust the vacuum advance with a 3/32" allen - if the car is jittery/surges under part throttle, adjust the vacuum counter-clockwise in small increments until you've dialed out the jitterbugs.
I'll fool with that once this other stuff is settled.
Thanks!
 
Lotta back&forth here. You have to remember that centrifugal advance when set on an adjustable dist.plate is half what the engine/timing light sees. 12* limit in dist. is 24* on the engine itself. Didn't want anybody going crazy trying to figure it out.
 
HALIFAXHOPS said:
PM the dist number and I can give you the factory specs at least to start with to get a baseline. Remember specs the total is mech adv + vac advance = total advance.
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Thank you!
I kinda know already what it does, since I set timing initially once the car was running to give me that "magic" 35-36 degrees BTDC at a little over 2000prm (FSM says 38 actually, but close enough for now - I have a mark on my balancer right at the 35 degree mark to aim with). That in turn gave me the initial idle setting (about 13BTDC) by default, which is fine - she runs real nice at idle at 800rpm.
Oh, as an aside - this setting gave me my best vacuum reading at idle as well. :)
 
As far as vacuum advance, it has been mentioned that it will give you better fuel economy but it will also make your engine run cooler and give you better throttle response from cruise.
There is absolutely no reason not to run vacuum advance on a street driven car.
 
440+6 said:
As far as vacuum advance, it has been mentioned that it will give you better fuel economy but it will also make your engine run cooler and give you better throttle response from cruise.
There is absolutely no reason not to run vacuum advance on a street driven car.
Click to expand...
And as stated, I shall try to once I get the carb situated.
Hopefully, I can get one of the (3) electronic distributors I have to allow me to by being able to eliminate the jitters.
Thanks!
 
TxDon said:
When it comes to advance curves everyone's experience is as different as the equipment on their cars. My car came with an unknown cam that sounds a lot like yours, same carb, and an MP distributor with about the same timing settings as yours. It would not run right with vacuum advance connected just like yours and seemed to not pull as hard as I thought it should. I ended up limiting the centrifugal advance to 16 degrees and bumping the initial to 20 degrees, it made a big difference in all around running and it pulls more like it should without any negatives. I have not tried using the vacuum advance since I did this but I will at some point.
Click to expand...

That is what racers do. Lighten up the centrifugal so it comes in early, limit the amount it adds so they can get the initial set with more.
 
TxDon said:
When it comes to advance curves everyone's experience is as different as the equipment on their cars. My car came with an unknown cam that sounds a lot like yours, same carb, and an MP distributor with about the same timing settings as yours. It would not run right with vacuum advance connected just like yours and seemed to not pull as hard as I thought it should. I ended up limiting the centrifugal advance to 16 degrees and bumping the initial to 20 degrees, it made a big difference in all around running and it pulls more like it should without any negatives. I have not tried using the vacuum advance since I did this but I will at some point.
Click to expand...
I too have my total advance limited to 36 degree with 16 degree of mechanical advance, 10 degree vacuum advance , and 10 degree of initial advance. If I dis-connect the vacuum and bump my initial to 20 degrees, as you have..have you had any starting problems with kick back or any other? ............................MO
 
Cornpatch MO said:
I too have my total advance limited to 36 degree with 16 degree of mechanical advance, 10 degree vacuum advance , and 10 degree of initial advance. If I dis-connect the vacuum and bump my initial to 20 degrees, as you have..have you had any starting problems with kick back or any other? ............................MO
Click to expand...
No, I have not had any starting problems. I did recently try reconnecting the vacuum advance using the ported vacuum source but I had the same problem I had before with bucking and surging at lower speed steady cruise conditions. I did not try adjusting the vacuum can and still need to try that.
 
Ported Vac is for Emissions controlled engines with a OBD 1 computer controlled timing events based on the emissions sensors
Constant Vacuum is for pre-emissions vehicles with No Computer timing controls.

the 284 cam is 240's at 50 and should be set up with 20* initial, 34 total on the mechanical and a low vac canister that will read as low as 10" and set to 10* so you'll get 30 at idle and 40-45* at part throttle cruise. Connected to a Constant Vac Source.

We had a Eddy carb here once, then we bought a screen door so we didn't need it anymore.

My opinion but I've only set up probably 100,000 distributors in 50 years.

Ebay search "Mopar J685"
 
Just curious but have you pulled vacuum on the vac advance to see if it is holding vacuum? If the diaphragm is shot it will cause weird issues.

Have you tried it on manifold vacuum barb?
 
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