[dlw6767]

cking the timing in my 65 gto 400 tripower motor i just put in recently. stock dist,pertronixs, 66 tripower vacuum advance. cam is not stock seems to like 12-14 degrees idle..i set it back today to 10 and run the rpms up to 3,000 and ckd my total timing, it showed like 50 degrees, isnt that a bit much total timing? where should it be? i know each motor has its own curve but is this right for it or should i just install a adjustable advance and set it up for what total? 32-36?

[Tim john]

Usually between 32 to 36 for total is in the neighborhood. Are you plugging off your vacuum advance line when you are adjusting your timinig ? you should be. 50 degrees ...that is way too much.

Tim john---

[68 Firebird]

yes it sounds like the vacuum adv is still hooked up and doing its job well.

my bird will have 46 degrees of advance if i raise rpm's to 3000 and leave vacuum adv connected. I run 10 inital 24 from mechanical and 12 from vac adv(ported).

Always plug vac adv when checking inital and mech curve. most important to plug when running manifold source to vac unit.

Also initial reading must be Rock Steady!!! Learned that one the hardway myself. Idle rpm will flucuate.

Gerry C.

[dlw6767]

i was cking it at base timing with vacuum unhooked and plugged. cking full timing with advance plugged in. my vacuum source is not ported as it should be, so your saying i should ck the full advance with vacuum line plugged off? then when plugged in it could be even more?

[67drake]

Yes.
"Total" timing is initial with mechanical "all in" but without vacuum added. I see the term "total" used by some people when they include the vacuum advance,so I usually ask if they are including vacuum to that figure or not to avoid confusion.
I run 12 initial,24 mechanical,for a total of 36. If I add vacuum in that's another 12,which gives me 48 degrees at cruise.

[dlw6767]

ok thanks! ill ck it again..

[68 Firebird]

X2!!!!!!!!!!!!!!!!!

[Stuckinda60s]

Are you sure your vacuum advance is supposed to be ported?

[lust4speed]

Up to 52 degrees with the vacuum advance connected is OK on most engines. You know the vacuum advance is coming in too soon (or too much) if you get mid range pinging rolling on the throttle, but not at full throttle. I wouldn't worry about the vacuum advance unless it gives you problems.

Also the stock weights in a 66 distributor probably won't hit full advance until about 4,600 RPM*, so be careful setting max timing at 3,000. A down and dirty way to check for total timing is to set it where you think it is correct, then stop the engine and remove both springs. Then you only have to idle the engine and the weights will swing out to full advance position. Much safer than revving the engine to the moon.

*Just set a '66 GTO 389 distributor up that did hit full advance at 4,600 RPM. And the springs were loose at idle so the distributor had already added in 2° at the 650 RPM idle. I ended up with no mechanical advance until 850 RPM and full advance arriving at 3,200 RPM. I also had to limit the total advance because the distributor was adding 32° engine degrees just on the mechanical advance.

[dlw6767]

ok here are my findings.. vacuum line unhooked and plugged..base timing 12 degrees..2,000 rpm i show 35 total degrees...at 3000 rpm i show 40 total degrees...i took the weight springs off next and at idle i have 42 total degrees. with the vacuum line hooked up at 2000 rpm i have 50 degrees varying and at 3000 rpm i have 55 degrees varying. so what do i need to change here to make this right? heaveir springs on the weights?

[dlw6767]

the last test is with the springs back on the weights of course

[Rugratman]

I run one light and one medium spring. My car seems to love that set up.
MSD dizzy.

[melwff]

you have to replace the stop bushing for the advance mechanism. From the factory it is made of nylon and is probably gone. The spring kits comes with a brass stop that you have to insert with the distributor out of the car and disassembled.

[dlw6767]

so thats why there is so much mech advance because of the bushing?

[chuckies76ta]

X2 Post #13..

Disconnect vacuum and plug port on carb.
Find your inital timing. Engine idling and rpm set. Example 12*
Removing the springs to find your mechanical advance is an excellent idea. Do that to find Mech advance. Example 20*

Now all you have to do is limit the stop bushing on the Distributor to give you that 20* or what ever mechanical advance you want.. Do with Springs removed so you don't have to race engine.

Once you have that now you have to select two springs that will give you your total timing all in by a certain RPM.. Example 12 + 20 = 32 degrees all in by 3000 rpm. You can change your initial to 14* to give you 34* total.. 14+20= 34*

The springs job is to add mechanical timing as RPM increases to a point where the stop bushing is located on the distributor. A weak spring will allow the timing to start coming in early and too stiff a spring will delay timing till the rpm gets higher..

Now you can Taylor your vacuum advance for fuel economy and part throttle driving... I like using manifold vacuum for the vacuum advance can..

I read not to go over 50* with inital, mechanical, and vacuum timing.

The vacuum cans can be a little tricky.. You need one that will work with the vacuum the engines makes. The cans also have different ratings. Some will activate on lower vacuums, some higher and add different amounts of timing. Just remember that if the can is rated to add 7* timing that it actually adds 14* off distributor timing. GM still has the B28 can which works really well..

Charles

[chuckies76ta]

Originally Posted by dlw6767

so thats why there is so much mech advance because of the bushing?

Yes. Study the Distributor to understand how it works.. If the mechanical part of the Dist. didn't move at all, you would only have inital timing.

With the springs off, you will be able to move the mechanical part of the Dist. back and forth.. You will see how far it moves. There should be some sort of stop to prevent it from open too much..

The more it opens the more timing it adds...

When the engine is sitting idling, the job of the vacuum can is to add timing by opening up the mechanical advance some to a point.. As RPM's increase, manifold vacuum drops out the vacuum can, and mechanical timing takes over.

I have a hard timing explaining myself through a keyboard.. I'm hoping you get the picture..

Hopes this helps.
Charles

[dlw6767]

yes i do understand everything you wrote here. i took my dist apart today and i see where the mech. advance would hit to stop it. it does not have any kind of bushing on it and looks like a clip would hold it in place? the little brass ones i got with my recurve dist kit i thought were for on the vacuum can but dont fit that. they do fit the post under the mech advance but limit the amount the plate turns quit a bit, maybe to much...do they have different bushings for that to set the total mech curve? also when the brass piece is slide on it wont stay,it covers up the little edge where you could install a clip. i looked at my 67 pontiac service manual for a breakdown of the dist and they dont show a bushing on that. i looked at another old dist i have and that doesnt have one either. so i file this brass bushing down so i can clip it on then ill need to reinstall and ck the mech advance running,weights off,at idle to get my full mech advance, sound right? and it could be too thick so i may not have enough mech advance....seems like i remember seeing like a clear plastic bushing on these?

[dlw6767]

heres a pic of it..how much thickness in abushing would i need to say change it 5 degrees? where can i buy assorted bushing kit for this? guys that set up dist on machines must get them somewhere..or better yet what is the thickness of the stock nylon bushing?

[lust4speed]

Your findings are in line with what I suspected you would find. 42 - 12 = 30 engine degrees mechanical advance added it. Now you can run your initial timing at 6° and end up where you need to be, but if your engine prefers 34° or lower, then you are getting pretty low on initial advance. Most of the time, it nice to see the distributor supplying between 20 and 22 degrees maximum so you can set initial between 12 and 14 degrees.

I would slightly pinch the copper bushing into an oval shape so you have to tap it on, and use either super glue or Loctite Red to keep it in place. While setting up the stop is pretty easy on a distributor machine, it becomes a royal pain taking it in and out of the car testing for max mechanical advance. You can file the bushing to increase the timing spread.

The real benefit is you won't have to worry about timing creep at higher RPM's - when it hits the stop, there won't be anything added after that point.

[dlw6767]

this cam doesnt like 6 degrees it likes 12-14 much better..i put the brass bushing in today and found a clip to hold it. tomm i will fire it up and ck the full advance again. if its too low i will pull it out and file it down some. looks like i need to change it about 8 degrees from where it was..42 down to 34-35.. I cant wait to get this done so i can get the hood back on!