Runs better with vac advance unhooked (Help)

[rich weyand]

Rich a distributor is a distributor... they all do the same thing. The link you posted has a really trivial issue that I wouldn't even consider a problem. Just get some new springs and weights and tune away which I would do with any dizzy. Now if it was the issue msd had with their streetfire dizzy ignition modules and coils going bad in the middle of nowhere then ya I'd be hot...
My setup is simple. I speak of crankshaft degrees( the number your going to see with your timing gun) engine running at normal temps using the timing tab or tape I find my 8 or 10 degrees of vac advance. Same applies for total and centrifugal...

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OK, so you are running 33* advance at rpm with your foot in it, and about 42 degrees at rpm in cruise. Interesting.

 

[350runner]

Ya it's all in the centrifugal. This was my best ignition upgrade. This has the same effect as throwing in a cam with a wider power band and little more lift than stock. Be ready to rod and jet if your running lean. Try it, you'll like it bud trust me.

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[rich weyand]

Nah. I was surprised that your timing is so conservative. I was just thinking that engine of yours would really like another 3-5 degrees of advance on the base timing to get into the 36-37* range all in. That would really light it up. You might give it a shot.

I'm running 17* base, 20*centrifugal, and 15* vacuum, for 37* WOT at rpm and 52* in cruise, which is right at the edge of "don't go more than this".

 

[350runner]

Nah mine's where it the engine wants it. Key is to provide the engine with as much centrifugal as it can take without ping. Initial really means nothing it's all in the total.

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[rich weyand]

Base timing is what is running your engine out of the hole. So base timing matters until the rpms come up. With a 2500 rpm lock-up in the torque converter, you're right. With a tamer torque converter, base timing matters.

But even if you were right that total is all that matters, you should be running closer to 36* base+mechanical for best performance. You don't have to take my word for it, that's what ignitionman said, again and again.

So you're about 3* short of where you should be with base+mechanical for best performance, and 13-15 is not too much for base timing, so you could just dial in the extra on the base timing and be there.

But, hey, do what you want. I'm just trying to be helpful.

 

[350runner]

34 to 36 is what he says.. so with 12 initial+ 22 centrifugal how am I short? It's all in your own preference. Of what you want to run. If I fell the need to try out two more degrees I'll just modify the center plate. I think it's safe to say we agree to disagree. No hard feelings bud

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[350runner]

Sorry for going on rich... let's think here how much time does initial really matter? Depending on your advance spring set when the centrifugal kicks in @ say 1000- 1500 rpm what does initial really matter. You say it matters cause it gets you rolling... how long does it take till the initial is out and centrifugal is in...

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[rich weyand]

34 to 36 is what he says.. so with 12 initial+ 22 centrifugal how am I short? It's all in your own preference. Of what you want to run. If I fell the need to try out two more degrees I'll just modify the center plate. I think it's safe to say we agree to disagree. No hard feelings bud

Ah. You said 10-12, plus 22, so that could be as low as 32 all in. 12 plus 22, you're good. I'd still dial in the extra two on the base timing, but whatever.

 

[73 C10]

Hey Rich, good to see you over here.

You guys might have your different opinions, but your both providing useful information to me to think about. I'm learning a lot. So thanks.

The truck has some kind of unknown aftermarket cam in there. It's got the sweet lumpy idle.

I'll pick up some timing tape and try a couple things. I'm sure if I get mine running like either of yours I'll be happy.

Another question:

I rebuilt the carb (1406) recently and I forgot to record the needle size but I saw the primary and secondary jets said 120 and another number I couldn't read. Is that too much jet for my set up (see sig)? I think it might be rich but I don't have the greatest feel for this. Should I invest in a Edelbrock jet kit, distributor weight kit? This truck isn't my daily driver but it will be mostly street and some dirt. I'd like it to be more muscle truck then daily driver. Iv'e never run a 1/4 mile so tht would be fun. I need to get one of those lockers that goes in the open carrier.

 

[rich weyand]

Sorry for going on rich... let's think here how much time does initial really matter? Depending on your advance spring set when the centrifugal kicks in @ say 1000- 1500 rpm what does initial really matter. You say it matters cause it gets you rolling... how long does it take till the initial is out and centrifugal is in...

Centrifugal comes in gradually; I doubt you're all in by 1500, though with small enough springs you could be. Probably more like 2000, or even 2500.

Depends on where your centrifugal advance comes in and how fast, but it can't come in too soon or you'll knock like crazy. Cylinder pressures on the compression cycle are just too high to allow more than 18-20 degrees total. Higher-rpm lock-up on the torque converter helps, letting the engine spin up before hooking up.

Let's say you have 3.73 gears on 31" tires. That gives 2500 rpm at 60 in third gear. In first gear, with 2.5:1 in the trans, you don't hit 1500 rpm until 15 mph, and 2000 rpm at 20 mph. Your base timing will dominate that portion of the launch unless it's a high-rpm torque converter that's slipping like crazy.

Usually to tune timing people I know dial in base timing until they get knocking, then back off a couple degrees. Then they set the advance to whatever it takes to get them from there to 36* all in. Finally they set vacuum advance off the base timing to get even idle, cut in by 2" less vacuum than the engine pulls at idle so the timing doesn't hunt. That is, if the engine pulls 14" at idle, you want the vacuum advance in by 12" so the timing is stable at idle.

Ignitionman did an example in a thread where he had an engine that wanted 12* BTDC at base. With 10:1 compression, it probably knocked at 14-15*. He then set mechanical advance to 24* additional to get 36. He only added 6-8 crankshaft degrees of vacuum advance to even out the idle, which is light for my taste in a daily driver, but OK. About halfway down the sixth post on this page. http://www.chevelles.com/forums/archive/index.php/t-625.html

 

[rich weyand]

Hey Rich, good to see you over here.

You guys might have your different opinions, but your both providing useful information to me to think about. I'm learning a lot. So thanks.

The truck has some kind of unknown aftermarket cam in there. It's got the sweet lumpy idle.

I'll pick up some timing tape and try a couple things. I'm sure if I get mine running like either of yours I'll be happy.

Another question:

I rebuilt the carb (1406) recently and I forgot to record the needle size but I saw the primary and secondary jets said 120 and another number I couldn't read. Is that too much jet for my set up (see sig)? I think it might be rich but I don't have the greatest feel for this. Should I invest in a Edelbrock jet kit, distributor weight kit? This truck isn't my daily driver but it will be mostly street and some dirt. I'd like it to be more muscle truck then daily driver. Iv'e never run a 1/4 mile so tht would be fun. I need to get one of those lockers that goes in the open carrier.

With the stock distributor with 20* mechanical, to get 36 all in, you should try 16* BTDC base timing. With the stock low-compression heads, you shouldn't get any knocking until close to 20*, so 16* BTDC is probably OK.

I have a very similar engine setup, and am running the following. I ran an NGK A/FR meter to get it right on the numbers. This should get you close. Note that you need the 1499 airhorn gasket(s -- five in a pack) to put it back together if you change the jets. Hopefully you also adjusted the floats, because they're always wrong.

secondary metering jets: Edelbrock 1426, 0.095" (stock jet)
primary metering jets: Edelbrock 1425, 0.092"
metering rods: Edelbrock 1441, 0.062" cruise, 0.052" power
step-up springs: 8#

Edelbrock doesn't make a .120 jet, so I don't know what's going on with that.

 

[350runner]

Man I really wish we could get ignitionman here...

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[rich weyand]

He still hangs out over on chevytalk.org.

 

[350runner]

Yea I'm a member there as well but that sites really like a ghost town compared to this one

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[73 C10]

Hey guys,

I've been driving it for a couple days now. I think it is 80-90% of the way to running good. It still sputters under light load, like cruising around 30 mph.