[Cliff R]

As mentioned in #6 you need to know where you are at now before you can determine where you need to go.

Here I use a degree wheel to tell me where the curve is at, then MIG welder to add some material to shorten the slot if/as needed for the pin. A POSITIVE stop is required on an HEI or it can/will continue to add timing at high RPM's once the weights meet the "flats" on the center cam.

Points distributors used a rubber pin bushing, HORRIBLE design there. I make stainless steel ones that you just drive in place and lightly crimp to replace the rubber factory sleeves.

This distributor stuff isn't that complicated, but does involve EXACT precision. I'll also add here that ALL aftermarket weight curve kits that I've encountered to date and nothing but pieces of bovine excrement. I've made a nice living removing that junk, installing factory parts, adding a positve stop for the pin, and modifying the VA if/as needed.

I'll also add here that at least 8 out of 10 vehicles that come in here for carb tuning will have distributor issues which are making them difficult, if not impossible for any carb to work well despite you, your friends, beer drinking buddies and all the "guru's" in your area to correct......FWIW.

HEI modifications are shown, pretty much the same thing for a points distributor. Also keep in mind that 10 degrees at the distributor is 20 degrees at the crank. Also, the amount of timing added by the vacuum advance can be measured and modified in similar fashion by welding up the slot and limiting the travel of the arm......

[bob prichard]

Originally Posted by Cliff R

As mentioned in #6 you need to know where you are at now before you can determine where you need to go.

Here I use a degree wheel to tell me where the curve is at, then MIG welder to add some material to shorten the slot if/as needed for the pin. A POSITIVE stop is required on an HEI or it can/will continue to add timing at high RPM's once the weights meet the "flats" on the center cam.

Points distributors used a rubber pin bushing, HORRIBLE design there. I make stainless steel ones that you just drive in place and lightly crimp to replace the rubber factory sleeves.

This distributor stuff isn't that complicated, but does involve EXACT precision. I'll also add here that ALL aftermarket weight curve kits that I've encountered to date and nothing but pieces of bovine excrement. I've made a nice living removing that junk, installing factory parts, adding a positve stop for the pin, and modifying the VA if/as needed.

I'll also add here that at least 8 out of 10 vehicles that come in here for carb tuning will have distributor issues which are making them difficult, if not impossible for any carb to work well despite you, your friends, beer drinking buddies and all the "guru's" in your area to correct......FWIW.

HEI modifications are shown, pretty much the same thing for a points distributor. Also keep in mind that 10 degrees at the distributor is 20 degrees at the crank. Also, the amount of timing added by the vacuum advance can be measured and modified in similar fashion by welding up the slot and limiting the travel of the arm......

Are you saying that if my MSD centrifugal is advancing 19 degrees, that translates to 38 on the crank? So that when I time it with 14 initial I actually have 52 degrees total advance? Thank you for your input.

[Cliff R]

No, I'm saying that whatever amount a distributor is advancing doubles at the crank.

For an MSD distributor if they are telling you it's 19 degrees advance mostly likely the mechanical advance mechanism is only moving 9.5 degrees.

The OP here is asking about limiting advance with a "bushing". Factory points distributors used a thin rubber sleeve on the pin and in most cases it has rotted away and the unit will be advancing more that it was originally set-up for.

I would not make or use a rubber or plastic bushing. I make them out of stainless steel here, and also use the MIG to add material if/as needed to get the advance curve exactly where I want it..........

[bob prichard]

Originally Posted by Cliff R

No, I'm saying that whatever amount a distributor is advancing doubles at the crank.

For an MSD distributor if they are telling you it's 19 degrees advance mostly likely the mechanical advance mechanism is only moving 9.5 degrees.

The OP here is asking about limiting advance with a "bushing". Factory points distributors used a thin rubber sleeve on the pin and in most cases it has rotted away and the unit will be advancing more that it was originally set-up for.

I would not make or use a rubber or plastic bushing. I make them out of stainless steel here, and also use the MIG to add material if/as needed to get the advance curve exactly where I want it..........

Ok, thank you.

[promptcritical]

Originally Posted by lust4speed

My first thought is you either have more advance than you think, or the compression ratio is higher than you think. For our lousy California 91 octane gas I set up aluminum headed engines to be between 10.2 and 10.3 true compression ratio, and set up distributors for 32 degrees with Kaufman heads and 34 degrees with the current Edelbrock heads. Cams are at least Stump Puller sized. We simply don't get pinging on the lousy California 91 octane gas with the above specs.

Hey Mick. How much of the total timing is initial and how fast are you bringing it in? Thanks..

[lust4speed]

My goal in setting up a distributor is 14 initial and all in just after 3,000. Sometimes the old re-curved distributors just won't cooperate and I might settle for 12 initial and around 3,200/3,300 before it's all in. I try and stay between those two examples. We get hot here and getting caught in freeway bumper-to-bumper traffic on a Saturday afternoon coming home from a show and keeping the AC running has taught us that sometimes less works best. At the track under better conditions where we are keeping things cooler I'll removed one of the springs and have the advance in closer to the old days by 2,400 or so. Just don't want to have it in that soon out on the street.

[promptcritical]

Originally Posted by lust4speed

My goal in setting up a distributor is 14 initial and all in just after 3,000. Sometimes the old re-curved distributors just won't cooperate and I might settle for 12 initial and around 3,200/3,300 before it's all in. I try and stay between those two examples. We get hot here and getting caught in freeway bumper-to-bumper traffic on a Saturday afternoon coming home from a show and keeping the AC running has taught us that sometimes less works best. At the track under better conditions where we are keeping things cooler I'll removed one of the springs and have the advance in closer to the old days by 2,400 or so. Just don't want to have it in that soon out on the street.

Thank you sir.

[dataway]

I ended up doing a ton of testing with a timing light ... came up with these four curves using various components.
Ended up using the green colored curve. (graphs are without vacuum of course)

[promptcritical]

Originally Posted by dataway

I ended up doing a ton of testing with a timing light ... came up with these four curves using various components.
Ended up using the green colored curve. (graphs are without vacuum of course)

I like the green one too, but in may case I'd be starting at about 12-14 which would give me about 32 all in. What components did you use (what's FatCam-524-37)? Thanks for posting that.

(I went to prototype, S3G, and then came back to S8G for Trident Design School after my first boat. Really nice place.)

[dataway]

You beat me to it, I was going to ask if you were a Nuke. I was student, then staff (SPU) at Marf.

"Fat Cam" was referring to the point cam on top of the shaft. I'm running a basically stock YS 400 (.040 over), 068 cam, about 10:1, auto trans, 2.93 rear, Q-jet, 2 1/4" exhaust, massaged factory logs ... very much a plain jane 400.

Distributor is a OEM 1111270
Shaft/Cam 1968265 (83 code)
Advance plate 1967914 (524 code)
Weights 1924737 (37 code)
I think I'm using one new OEM spring and the other a Moroso kit spring ... not sure which one.

The code numbers are what you would see stamped into the part. All of these parts with the exception of the one spring were the OEM parts for a 68 YS 400 GTO. I made a limiter bushing in brass to replace the OEM rubber piece. I used a common aftermarket replacement vacuum can that is often recommended on this forum ... I don't have the number at hand right now.

[promptcritical]

Originally Posted by dataway

You beat me to it, I was going to ask if you were a Nuke. I was student, then staff (SPU) at Marf.

"Fat Cam" was referring to the point cam on top of the shaft. I'm running a basically stock YS 400 (.040 over), 068 cam, about 10:1, auto trans, 2.93 rear, Q-jet, 2 1/4" exhaust, massaged factory logs ... very much a plain jane 400.

Distributor is a OEM 1111270
Shaft/Cam 1968265 (83 code)
Advance plate 1967914 (524 code)
Weights 1924737 (37 code)
I think I'm using one new OEM spring and the other a Moroso kit spring ... not sure which one.

The code numbers are what you would see stamped into the part. All of these parts with the exception of the one spring were the OEM parts for a 68 YS 400 GTO. I made a limiter bushing in brass to replace the OEM rubber piece. I used a common aftermarket replacement vacuum can that is often recommended on this forum ... I don't have the number at hand right now.

Marf…flush to scram? I still am a Nuke, just not for the Navy directly anymore.

Thanks for the info. Did you have the OEM parts or did you have to find them?

[dataway]

I had some, had to procure the others, not very difficult to find, bought 2 or 3 distributors off ebay to find good examples of all the parts I needed. Biggest problem was getting the sellers to look close enough to find the parts (codes) that were used in their offering.

Hey now, MARF was a pretty cool design ... only real problem far as I know was they could never figure out if it would go super or sub if rolled too many degrees ... kind of an important thing to know on a submarine But it would have been great for a land based plant .. none of that silly rod shimming.

Jeez, I haven't checked Wikipedia ... wonder if it's ok now to talk about MARF

[promptcritical]

Originally Posted by dataway

I had some, had to procure the others, not very difficult to find, bought 2 or 3 distributors off ebay to find good examples of all the parts I needed. Biggest problem was getting the sellers to look close enough to find the parts (codes) that were used in their offering.

Hey now, MARF was a pretty cool design ... only real problem far as I know was they could never figure out if it would go super or sub if rolled too many degrees ... kind of an important thing to know on a submarine But it would have been great for a land based plant .. none of that silly rod shimming.

Jeez, I haven't checked Wikipedia ... wonder if it's ok now to talk about MARF

I always thought it was a neat idea even if it wasn’t practical.

Thanks for the info. Need to not hijack this thread I suppose.