vacuum advance issues

[crazy longhorn]

Originally Posted by Erratic67

Thanks for the additional input .... If you begin from the start of this post you will understand issues I was having in the begining and now current. Trying to decifer fleetside is way over my head at this point. Thanks to storm, I have gained a lot of ground and very much appreciate.
1. Yes timing was set with vacuum advance disconnected and remains that way.
2. Pick up coil was tested and proven to be fine.
3. My tach. is not working correctly so total was set at 35* when the mark on the harmonic balance stopped rising when excellerated, "RPM was unknown"
4. I didn't check total when originally at 8 BTDC, which may have stopped the backfiring if I would have set the total @ 35* then.
5. If i choose to decrease initial back to 8 then reset total back to 35*, what will that hurt & do I need to find TDC all over again?

What Fleetside was saying, is that the curve on the dist is not ideal. You can recurve the dist, to get that 12-14 initial....best use stock weights/aftermarket springs. I like a Crane adjustable canister/spring set, & look for weights from a 3/4 or 1 ton truck (bone yard parts). You will tune the vac can last, & they all tune just a little differenty , according to gears/cams, ect. So I will try to be basic....IF, you say that she runs best with 35 on the total, that is where you should be! On that HEI, even with the "preferred" weights/centerplate, you will have 14-16 degrees initial, to hit that 35 total. use the spring combo that will let the curve "all in" @ 3000 rpms (2800-3200), & limit the vac can to 8 -10 degrees at the crank shaft. You should be in the ballpark. Any ?, ask as you play Longhorn

[storm9c1]

Right. Basically you start at some value, I suggested 8 degrees as an initial timing value at idle. Some SBCs can tolerate more, but usually no more than 14 degrees. As you rev the engine, the weights and springs under the distributor rotor "fly out" and advance the timing until it hits the stops. Once it hits the stops, it will stop advancing. Whatever timing reading you get here is your "total" mechanical timing. Most SBCs like 28-32, but some can go as high as 36 here.

If yours likes 35 total, that's fine. You have your "all in" value. But what concerns me is your initial value when you have it set for 35. And you said it was 19 (which is too much IMO). Subtract the two and you get 16 degrees. So that means that your weights and springs are only allowing 16 degrees of travel. I don't like that. You need a weight and spring setup that gives you at least 20-24 degrees of travel to get the best curve for a street vehicle.

So....... next step is to pop off the cap and rotor and study the weights and springs underneath. You may even have "stop bushings" installed on on the pins that the weights hit to control their swing. A good picture of your weights and springs may help us help you.

Longhorn was saying that you may need to change these out, which is VERY common to do to solve these problems. Even just changing the weights may give you more travel because there are different weights you can buy or pull from a junk car that is shaped differently and allows more travel. The weight and spring kits they sell sometimes come with different size stop bushings which can also limit the travel of the weights.

This might be why this distributor was for sale............. You could always swap the weights and springs from your old distributor. That alone might give you better range. I have the opposite problem with the last MSD Streetfire I bought. It had too much range in the weights and springs and caused bad pinging. Using the weights from an old MSD distributor solved that.

Did the car this came off of have a radical cam? Some cams like a ton of initial timing so a 16 degree spread might be perfect for something with a radical cam. But no good for a stockish engine...

[geezer#99]

Maybe this link will help him figure it out storm.
http://www.crankshaftcoalition.com/w...EI_distributor

[crazy longhorn]

Originally Posted by geezer#99

Maybe this link will help him figure it out storm.
http://www.crankshaftcoalition.com/w...EI_distributor

From one geezer to another....that link was a good read, should explain pretty much all I agree with Geezer, Storm & Larry, with the curve....but will just add that ,if you are new to this....please do not hesitate to ask questions? That is why we are here.....longhorn

[Erratic67]

Sorry for the delay, internet issues .... Here is a pic of my distributor. My best way to describe the springs is that there is not much resistance when moving the arm's that are stamped (60) by hand, don't know how they should be but these seem kind of loose.
I decreased my total to 34*, no change with initial nor did it change performance, my 350 is primarily stock, I'm assuming the cam may be slightly above stock. Don't know much about it as I purchased it this way.
It seems to be running fine as far as I know but how will I know if its running at optimal timing or not?
What indicates where initial timing should be set as the starting point?
Do I keep adjusting initial/total until it begins running poorly then adjust back until it runs good?
When I connect vacuum advance what change should I expect to notice?

[crazy longhorn]

I have read the the... Page,... and, feel that if the weights/pins are loose,or sticky... you have issues. shoot for the 3'4 to 1 ton weights/centerplate(best curve). Understand that the HEI will kickobout 20 degrees on mechanical....I would suggest 14 initial, to hit a 34 total....after that, a 8-10 degree vac advance, but you might do 12 (cam issuies)? You have my PM.....I can talk faster than I type Welcome ,longhorn

[storm9c1]

OK, those are GM weights and center plate. That helps. What are the numbers? I can read the #60 on the weights. But what's the center plate? #406 or #408 or what? Having this info, we might be able to research the timing curve this combo should produce. Either way, I think you need to pull that all apart and get all that rust off. With the way it looks now, it may not operate smoothly.

[crazy longhorn]

Dave, was the ign guru, that new the numbers on the weights....but basically, he said pull em ..from a 3/4 ton truck, what you will get, is a far better curve, than you will see on a car dizzy. Me & that old man butted heads pretty hard......but he knew his ****! Not too bad in my spot....the last tune on my 383....(beat up old junk dist/750 edel, went 12.9, in my bros truck@ the track. I cost him 1500 bones, to get that 12.5 ride....IMHO, not to bad, for a street ride? street/ tune @ 12.9....longhorn

[Erratic67]

The center plate is #406 ....
Where can I purchase the weights, center plate and springs and what type, size and spring tension I need?

[crazy longhorn]

Bone yard , on the weights/center plate.....I would go Crane on the canister/springs. Understand, that the 3/4-1 ton trucks had a better curve, than the 1/2 tons ,or cars had.....the big trucks , just were not fitted with emission parts (76-79 3/4 or 1 ton), for the best weight set. do not try to play with aftermarket "lite weights", on the HEI.....they flat wont work, been there, tried that! I can explain it better.....pm me, I will give you my cell ...as I said, I can talk faster than I can type.. Longhorn

[Erratic67]

I could be wrong, I'm pretty sure it's #408 .... Will it hurt anything for me to drive the truck as is until I receive the distributor parts, cause it seems fine without any issues?

[storm9c1]

I don't think it will hurt. Just listen for pinging since you have a ton of initial timing. When it gets hot, you may get some "kickback" on the starter with too much initial timing and that can break the starter. So keep an eye out for that.

You can keep the vacuum advance disconnected for now. Your MPG will suffer, and your truck won't be the "greenest" truck on the planet emissions-wise. But it should feel normal otherwise. Keep an eye on your temp gauge while cruising the first time if you do any highway driving. The extra timing from the canister also helps it run a little bit cooler.

Let's not touch the canister until you get the weights and springs sorted out first. If Longhorn is offering his advice over the phone, I'd take him up on it. We got some good people here... That's why I like this forum. Cool cats here for sure.

[Erratic67]

Longhorn .... sent u a pm, need some info regarding springs/weights. At your convenience, give me a buzz.

[crazy longhorn]

The Crane canister/spring set , that I was referring to....Crane # 99600-1 or jegs # 270-99600-1 (for GM HEI). It is listed for $38.50, & while you may find some a tad cheaper, they do not offer the springs & limit plate Longhorn

[crazy longhorn]

Originally Posted by storm9c1

I don't think it will hurt. Just listen for pinging since you have a ton of initial timing. When it gets hot, you may get some "kickback" on the starter with too much initial timing and that can break the starter. So keep an eye out for that.

You can keep the vacuum advance disconnected for now. Your MPG will suffer, and your truck won't be the "greenest" truck on the planet emissions-wise. But it should feel normal otherwise. Keep an eye on your temp gauge while cruising the first time if you do any highway driving. The extra timing from the canister also helps it run a little bit cooler.

Let's not touch the canister until you get the weights and springs sorted out first. If Longhorn is offering his advice over the phone, I'd take him up on it. We got some good people here... That's why I like this forum. Cool cats here for sure.

Totally agree with Storm....get the weights /springs sorted 1st As said, check you pins for wear 1st, & be sure that when you twist the rotor , that it will "snap" back. The canister that I suggested, does not need to be in the mix to start....use the springs (blue/silver would be a good start point, should get you "all in" around 3000-3200. From what we talked, I feel that 35 is too much , on total. Let us know what 32-33 does, & where does the initial fall ...after? Best of fun, any ?, just ask....longhorn

[Erratic67]

Longhorn ..... Thanks for taking the time out of your schedule to contact me and explain in detail, possible issues and resolutions to my problems.
Soon as I receive the springs/canister and have them installed, I will set my timing again. I'll keep y'all informed as to how it goes. Wish me luck.

Does the term "all in" refer to .....
When my timing stops advancing at that given RPM?

[crazy longhorn]

Originally Posted by Erratic67

Longhorn ..... Thanks for taking the time out of your schedule to contact me and explain in detail, possible issues and resolutions to my problems.
Soon as I receive the springs/canister and have them installed, I will set my timing again. I'll keep y'all informed as to how it goes. Wish me luck.

Does the term "all in" refer to .....
When my timing stops advancing at that given RPM?

Yes, "all in" is where you are, with initial+ mechanical... total is the sum of both (all in).vac advance un hooked+ plugged....revved to that 3000 rpm spot. Worry about the vac advance later. Longhorn

[Erratic67]

Sorry for the delay but finally got around to working on my truck again .....
Cleaned all the weights, plate and springs rust free. Set initial @ 8* BTDC, 3000 RPM,s
"all in" @ 26* ..... Advanced timing to "all in" @ 30*, initial now at 14*.
I have the different springs and weights but did not change them as of yet, until I received advice from y'all. What should my next move be?

[fleetsidelarry]

Originally Posted by Erratic67

Set initial @ 8* BTDC, 3000 RPM,s
"all in" @ 26*
..... Advanced timing to "all in" @ 30*, initial now at 14*.

Erratic, I'm sorry that I was not more clear before. I meant no disrespect and didn't intend to confuse.

the latest info re-affirms what you have been saying all along. your current combo of springs/centerplate/weights gives you 16 degrees of mechanical advance. as the guys have said, you probably want more like 20-24.

if you bought a kit it should have come with a chart of what amount of advance the different combinations of springs will give at what rpm.

- pick a spring combo that doesn't start advancing 'til after idle speed (important) and gives the desired max at 3000.

- if you want, if you can post a picture of the chart we can point out which combo we think will get you the desired results

[Erratic67]

Here's the chart, hope this helps

[Erratic67]

Heres another

[fleetsidelarry]

those help me a lot, Erratic. especially the 2nd photo 'cause I was having trouble reading the stop bushing colors on the first photo

if you want 20 degrees @ 3000 it looks to me like you'd go with curve "D" (2 blue light springs) with the blue or purple stop bushings. I think if you use this combo and set your total at 34 you'll end up with 14 initial

EDIT: I just realized that the kit you bought is apparently the MSD kit for their distributors. I'm not familiar with stop bushings, the MSD kit I have for my GM distributor (http://www.summitracing.com/parts/msd-8428/overview/) didn't have them. I'm guessing that the bushings don't work on the original GM. this is what my curve looks like: http://static.summitracing.com/globa...8_frm28648.pdf if I use 1 light spring and 1 medium spring my curve is about right (in between using 2 lights or using 2 mediums)

[Erratic67]

I changed my stock springs to the blue ones but there is no bushings that fit in my weights, without the bushings they do have some play and feel pretty loose. With that said, I set my initial at 7* BTDC and at 3000 RPM's "all in @ 27* ..... Advanced distributor to 34* and initial increased to 18*
Maybe I should try installing the aftermarket weights & backplate that came with the bushings to see how that works out, what do you suggest? Another question I have is how does that backplate come off?

[fleetsidelarry]

Originally Posted by Erratic67

..Maybe I should try installing the aftermarket weights & backplate that came with the bushings to see how that works out, what do you suggest? Another question I have is how does that backplate come off?

Yes, all the pieces of the advance kit are intended to work together.

the advance "curves" shown in those charts you posted are a product of the shape of the scroll plate (what you're calling the backing plate I think), the shape and weight of the weights, AND the springs. how much advance (16 degrees in your case) is based on the shape (see note **). the RATE that the distributor advances (how quickly it reaches those 16 degrees) depends on the springs. changing only the springs changed only how quickly you got to 16 degrees. (**the springs CAN affect the total if they are too heavy to allow full travel of the weights at a given RPM or too light to allow the weights to fully retract at idle, don't worry about that just now) you should be checking your initial at the same idle speed each time, preferably fairly low 6-700 rpm

in order to change your total you need to swap in the new plate and weights.

the plate is held in by "e" clips on the posts that hold the inner loop of the springs. take those e-clips off and the plate should pry right up and off. only thing that would interfere would be rust on those posts

[Erratic67]

okay thanks ... umma remove that back plate and replace everything with the new parts in the kit. I have been told that aftermarket weights / back plate does not work as well as stock but what will it hurt to try, i'll post my results when done. Thanks again