Vacuum Advance Adjustment?

[saxman]

I recently completed the Duraspark upgrade for my rig. I put the light springs in the dizzy. I have been getting some pinging going uphill at 60 MPH. I disconnected the vacuum advance and went up the same hill at the same speed with no pinging.

Sooo, I read an article on how to adjust the advance by inserting a 1/8" or 7/32 Allen wrench into the vacuum advance port and engage the adjustment screw.
well, i tried that and the allen wrench is way too big for the vaccum advance port. I had to go down three more sizes to finally be able to insert the wrench into the hole. Then, I tried to turn it and it just spins freely. I do not feel it turning anything.

I bought the dizzy at the Oriely's.

Click here for the article...

any ideas??

thanks for the help...

 

[72Sport]

I bought a rebuilt dist with vacuum advance. I took it to a shop because of other problems. The shop owner said the rebuilders left out the adjustment screw and stop in the vacuum advance. He installed a new vacuum advance.

 

[saxman]

i would think that I can just remove the vacuum advance and replace it? right? or, do I have to pull the entire dizzy?

SS

 

[72Sport]

i would think that I can just remove the vacuum advance and replace it? right? or, do I have to pull the entire dizzy?

SS

You should be able to remove it on the vehicle if you have room to get to the mounting screws. Just don't drop anything down in the dist. It has been quite awhile and I don't remember what is on the inside but the shop owner replaced it on the vehicle.

 

[saxman]

if I insert the allen wrench in that the port, how far does it go in? Do i insert it all the way until it stops?

also, should I feel resistance if I am actually adjusting it? last night, it just felt like it was spinning freely..

 

[68 Broncoholic]

Get a new one. Comes off with 2 screws and while you're there shine a light if you can inside to see if there is an adjusting screw in it. I never knew there was such a thing. I always sucked on the hose and if my tounge didn't stick to it (vacume) the part needs to be replaced.

 

[ransil]

if I insert the allen wrench in that the port, how far does it go in? Do i insert it all the way until it stops?

also, should I feel resistance if I am actually adjusting it? last night, it just felt like it was spinning freely..

Should go in at least 1".
Should be some resistance, you are either missing the Allen screw or your wrench is too small.

This may not solve your problem, adjusting the diaphragm only controls how far it moves with x amount of vacuum applied.

Total advance = Initial + mechanical + vacuum

What is your initial set at??
Might need to back it off a bit.

Total should be around 30-35 degrees.

 

[broncnaz]

You might have springs that are to light I tend to run slightly heavier springs with intial and mech advance totaling 34 dergrees then letting the vacuum take up the gaps pulling a hill your vacuum should drop and the vacuum advance should not be advancing anyways. Total advance for 302's is usually good between 34-38 degees all in by 3000 rpm.
Here's another link to some setup hints
http://www.cranecams.com/pdf/271e.pdf

 

[72Sport]

Without the adjustment screw and stop you have no control on total advance. Mine had 57 degrees total without the adjustment screw and stop. A bit too much. Fortunately it was stock and I didn't end up with any holes in the pistons.

 

[Bronchole]

I thought that the "weight" of the springs only effects the curve that the mechanical timeing advances on and has no actual effect on the total advance. For the mechanical advance that is controlled by the mechanical advance stop.

If this guy has determined that the total advance at a given driving condition is too much and he needs to back off the stop for the vacuum advance to correct it why would you change the initial timeing? wouldn't that decrease the performance gained by the correct timeing across the entire rest of the RPM range to incorrectly fix a problem at one range?


saxman, make sure you add several grains of salt with the advice you get.

There are aftermarket kits (I think Accell for under $20) to replace the vacuum advance. If you distributer is new you should take it back and have it warrentied.

 

[saxman]

I am a bit lost now...

i did put the lighter weight springs in the dizzy. I do not know what the total advance is yet, which is measured in degrees. I am not familiar with that yet and how to calculate it. I just need the time to read about that.

The only numbers I do know is what my main timing is at. BTDC = 10 degrees

Sooooo, will adjusting the diaphram fix this pinging problem with the vacuum advance is connected?

I will look at it again tonight, but I do not think that there is anything to turn in the that diaphram. I stuck that allen wrench in pretty far. the wrench was the biggest one I could use that would fit in the hole. The diaphram might need a bigger wrench, but anytjhing bigger will not fit through that nipple!

Should I replace the diaphram first? or, should I yank the dizzy out (which I rather not do) and put the heavier weight springs back in?

This is a fresh rebuilt engine, 351W BTW...the truck accelerates great off the line, good power, just under load and up hills does the pinging happen..

thanks guys for the info...

 

[broncnaz]

You should be able to look through the slot in the breaker plate(my previous post should show this) and see the advance plate there a slot about 3/8"wide or so with a pin in the slot That is the one that controls the advance. the amount of advance is stamped in the advance plate there should be another one which is open or has no pin to stop the advance. Distributer advance is doubled at the crank so if you run 10 degrees initial and your dist is setup in the 12 degree slot it will have 24 degrees advance at the crank for a total of 34 degrees then you have to factor in the vacuum if you adjust it to were it barely works than you should be good as you want all the advance you can get from the mechincal and initial before worrying about the vacuum.
Sounds like you may have set the advance in the highest setting I've seen ford dists with a 16 degree slot with would be way to high that coupled with light springs on a heavy vehicle could be a big part of your problem. Double check your mechanical advance setting if its 10 or 12 then you should be good then it may just be that the springs are to light you might want to try 1 light spring and the stock light spring. the vacuum advance usually gives 8-10 degrees advance so double that at the crank you need to lessen the sensitivety of the vacuum advance. You can always run with the vacuum advance disconnected as it mainly used to fill the gaps in the heavy spring advance curve of a stock system. Try a 3/32 allen wrench to adjust the vacuum advance. I think the stock ones use a 1/8" but aftermarket is 3/32"

 

[saxman]

I am going to get this vacuum advance kit and install it first since I can't get the allen screw to adjust the current diaphram I already have.

I will report back after the holiday.

Since the truck is running fine with the vacuum advanced plugged right now, this targets the problem to the vacuum advance. If not, I will dig deeper.

Thanks again for the help...

 

[76 bronco J]

I 'd like to throw in some more confusion I run from the manifold vacuum port on the carb-- the above are true to a point--vacuum is factored into the timing only at part throttle or also at idle if it's hooked to the manifold vacuum on the carb-- the manifold & ported vacuum on the carb are only different when the throttle is closed-- hook a gauge to both & you will see after the throttle is barely open they are the same & that at about 2500 or so they both taper off together & ported doesn't just keep rising & advancing the timing more & more like alot of people think--in the end regardless of the intial timing or amount of vacuum advance deployed or when(there will be none at upper rpms) at open throttle most small blocks like 34-38(that is the true total timing)-- do no take my word or anybody's until you do plenty of research with trial & error then come to your own conclusion-- I've explain some of the ways I've timed mine in other post but it's not stock, regardless try different things & go with what works--- type in (ported or manifold vacuum) on yahoo and see how many views there are on the subject------if this link works here's a good place to start, read the 3rd post--------- http://www.chevelles.com/forums/showthread.php?t=80222

 

[broncnaz]

Good article but like everything what works on one engine doesnt nessesarily work on another engine. I know if I set my initial timing to 10 degrees then hooked the vacuum advance up to manifold vacuum it wouldnt idle worth a crap and run so rich you could run another car off my exhuast. If I set my initial to more than 15 degrees it runs really rough and rich. Not to mention the intake backfires you will get with that much advance. So I dont see how they are coming up with this. They may be forgetting the vacuum delays that are installed in a lot of these manifold vacuum systems. Maybe I'll play with this theroy tomorrow I've got 2 dist's with different setups to play with on my 73. Might have to look at my bone stock 71 somemore also but thats a different beast all on its own with the dual vacuum cannister. with no other emmissions equipment to speak of.

 

[saxman]

Ok, I put the stock springs back in my dizzy tonight.

After everything was back together, I started her up. I did not realize how you can actually see the timing change as the rpm's increase. I now realize how you guys are coming up with your advance degrees from 30-38 degrees.

I also put the crane cams vacuum advance kit on the dizzy if I want to adjust the vacuum advance at all. The diaphragm that came with the rebuilt dizzy from oreileys was not adjustable, so I replaced it.

Ok, so at 10 degrees btdc initial, I rev the engine, and it was going way past 40. I figured with those lighter springs I was probably going way off the charts. I then set my initial timing to 8 degrees btdc and I revved the engine again and it hovered around 35 or so. I will rent another foot for the gas pedal so I can watch the timing gun.

Thanks for the help everyone. I will let you know how it rides down the hwy and up these hills in the hill country of Texas soon...I just fired her up in the garage tonight.

 

[Mikey]

You might have springs that are to light I tend to run slightly heavier springs with intial and mech advance totaling 34 dergrees then letting the vacuum take up the gaps pulling a hill your vacuum should drop and the vacuum advance should not be advancing anyways. Total advance for 302's is usually good between 34-38 degees all in by 3000 rpm.
Here's another link to some setup hints
http://www.cranecams.com/pdf/271e.pdf

HA!!! According to this pdf, it looks like you do NOT have to remove the distro from the engine to get to the springs!!! Whaaaaa....Hoooo!!!
Mikey

 

[saxman]

that is right! it is a very easy switch! I like how the springs are different colors in the kit!

 

[Mikey]

By the way, the springs control how soon the advance kicks in, not how much, hence the title "advance curve kit." The curve is controlled by the vacuum advance and the springs/weights. Now that you have it dialed in, try the lighter springs and see how that works. I think the 302 in stock form likes the initial at 6.
Let me know 'cause I just ordered the springs from Summit. I put the springs on the 68 Cougar and throttle response improved a bunch....but it's not stock....
Thanks,
Mikey

 

[broncnaz]

HA!!! According to this pdf, it looks like you do NOT have to remove the distro from the engine to get to the springs!!! Whaaaaa....Hoooo!!!
Mikey

Yeah but that spring clip in the top is a PITA to remove it may be easier to remove the Dist. As long as you set te engine to TDC and make sure the rotor is pointed to the #1 position and dont turn the engine over while the dist is out the dizzy will go right back in.

Even stock engines will benifit from a faster curve. Saw a article once on a stock engine with stock curve dyno test's show a 20hp increase with only the advance curve changed so that all the advance is in by 3000rpm