adjustable vacumn advance diaphram ?

[mikes51]

I've been trying to eliminate some pinging during light acceleration on hills (sbf). I just installed one of those adjustable vacumn advance canisters, the ones which you can adjust with a small allen wrench inside the canister.

I set it up at idle 8 degrees before tdc which the motor ran good at before, but it did ping before at 8. I then used the allen wrench and adjusted out per the instructions a couple of turns. Well, the pinging has stopped, but when I checked it out with a timing light, my timing is now at idle 3 degrees before tdc. Does that mean I could have just done the same thing, without the new canister, by turning the dizzy back retarded to 3 degrees before tdc?

[Deyomatic]

I think it is a bleeder valve, and that where as before when it was at 8 D BTDC, when you were cruising, it might give you 34 degrees D BTDC, while now, it will get less of a signal from the carb, so you might only be at 30 D BTDC when cruising.
I think.

[mikes51]

Deyomatic,
Thanks for the reply. Sounds like that is what's happenning. I know I tried running the car before at 3 degrees BTDC, without the new diaphram, and it was practically backfiring out the exhaust. Well, it's working now, that's all that matters.

[Deyomatic]

I was thinking about this yesterday. Does it ping AT IDLE? If so, it sounds like maybe your cam timing is off maybe. I'm not an expert, but I was always told that knock and ping were supposed to be under load. And if that is the case, I could see where it would only 3 degrees at idle. Ahh, the whole thing is confusing, I guess I stand by my original response. I hope you get it. When I did my timing on my Ford, I took the "backyard" advice of the guys on here. I had a timing light, but I'm really lazy. So, I kept the distributor hold down nut fairly loose and did a blast down the street. I just kept advancing it. They said to advance it until it knocks then back it off until it doesn't.
Is this a used distributor? If so, the previous owner probably has some funky advance curve going on with it.
Good luck.

[a/fxcomet]

What is the inital timing with the vac advance unplugged? Total? When is it all in by? What port do you have it hooked to?

[mikes51]

[ QUOTE ]
What is the inital timing with the vac advance unplugged? Total? When is it all in by? What port do you have it hooked to?

[/ QUOTE ]

Before I installed this adjustable vacumn advance canister, I set it at idle, no vacumn, from 10 degrees BTDC all the way to 3 degrees BTDC. Ported vacumn from carb and it used to ping at all those settings. It pinged when under load, mostly going up hills.

I then went and tried manifold vacumn, and it ran great, no pinging. Except when starting to accelerate, since there is no immediate vacumn, there was some hesitating. I tried then running 15 degrees BTDC, it helped but not totally.

Now I have an adjustable vacumn diaphram/canister on it, backed out a couple of turns. It is 3 degrees BTDC at idle, ported vacumn line disconnected. Total advance appears to be about 40 degrees, comes in about 1,900 to 2,000 RPM.

347, energizer cam, World products non alumin heads.

I'm happy with how it's running now, I guess the question is academic. Does the allen wrench adjustable vacumn canister just let's you retard the distributor in a convenient way (without actually loosening the distributor housing)? Or does it cut back on the amount of vacumn generated advance. I'm thinking now it is the latter just as Deyomatic described.

[Shiva69]

When you adjust it. you adjust how much pull the vaccum diaphram has on the timing.

Garth

[mikes51]

Shiva, thanks. Again, your avatar is quite good.

[jonizzle]

Mike51-

it seems like you figured out your timing. on my 289 i have 12* initial, 34* mechanical advance and 8* of vacuum (coming off the timed port on the carb) for 42* total timing. I am no expert on timing but am surprised that you are at 3* BTDC at idle. that seems too low and might explain the backfiring. 8-12* at idle is what i have heard to be a good place for our SBF's. and yes the adjustable vacuum advance canister only allows so much vacuum to be pulled (depending on how you dial it in) thus creating how many degrees of vacuum advance. basically you can only back off the timing so much with the vacuum advance by not letting it pull the vacuum then whats the point of having the adjustable vacuum advance. you could put stiffer springs in the distributor and that wouldn't let the timing get too high so fast. as i just typed that i thought maybe the springs in the distributor are getting weak and is allowing too much mechanical timing too soon. this could be causing the pinging. these are just some ideas and i hope this makes some sense.

[mikes51]

Jonizzle,
Excellent reply, I got all that. Yes, I'm just happy I can drive it around without pinging right now. So I'm running around right now at 3 degrees. I will soon start advancing (turning the distributor) and see if I can get back to that 8 degree or 10 degree range.

How did you figure out you had 8* of vacumn? I was revving mine up from idle with the timing light on it. I could see the timing mark move appropriately. But how does one know if it's the vacumn doing the advancing or if it's a combination of the vacumn and the weights working at the same time?

[jonizzle]

i was using a timing light that you could dial in the advance you wanted. so if i wanted 42* total of advance i turned the dial/pressed the up arrows on the light so that 42* was showing and then pointed down on my pointer the zero mark on my damper was at the pointer meaning i had 42* total advance.

I figured i had 8* vacuum advance because i first set my mechanical advance to 34*. again with the same idea as above. then i plugged in my vacuum advance and dialed that in to give me the extra 8* for a total of 42*. Now i wasn't the only one doing this, but my uncle is a great mechanic and he showed me how to do it. i haven't noticed any detonation but then again every engine is different and behaves differently with timing because of other factors.

I think that the weights and vacuum advance work together in producing the total advance. but i am not entirely sure on that. i do know that my vacuum advance is plugged into the timed port on my carb, so it is not pulling vacuum all the time.

[Crosley]

Often the vacuum advance will move the timing too far and needs to be limited.

A friend just had Bob Ream Sr. at B&R Auto near my work place modifiy his Ford 460 dizzy. Bob cut the timing advance vacuum way back and now the engine runs way better, smoother.

[a/fxcomet]

This is going from memory, but I think my 289 is set at:

12* inital at idle, vac advance disconnected
35* total mechanical advance, all in by about 2500rpm
25* with vac advance connected at idle
vac advance is connected to the manifold vacuum port

Runs good, and never had a pinging problem. I run the crap 87octane, but that is also due to the al heads. With iron heads, you might try a bit more total advance (closer to 40*). On my dads pretty stock 289, I can only run about 8* or 10* inital. That is due to a number of things, including the stock cam. No two motors are alike, but those numbers should get you in the ballpark.

[Humboldt Cat]

Has anyone tried adjustable vacuum advance kit Accel sells? Comes with dizzy plate springs of different weights (for the plate under the points), for different advances.
Any experiences with it?

[Humboldt Cat]

I'm sorry, MIkes51, didn't mean to hijack the post, just seemed a good time to ask.

[a/fxcomet]

[ QUOTE ]
Has anyone tried adjustable vacuum advance kit Accel sells? Comes with dizzy plate springs of different weights (for the plate under the points), for different advances.
Any experiences with it?

[/ QUOTE ]

Yea, used that on the old stock points dizzy. Worked good. The Duraspark I have now came with it stock.

[mikes51]

Humboldt Cat,
I bought the Crane version of the kit from Summit. It also came with a set of springs for the weights. This is a simplification of the very thorough instructions, but they have you do a "pedal to the metal" test with your vacumn line disconnected. If you don't ping, you don't need the springs.