Runs better with vac advance unhooked (Help)

[73 C10]

Like the title says, when vac advance hooked up it idles good. When I give it any gas it starts to miss (sputter). The sputter is all through the RPM range. I pulled the vac advance hose off the manifold vac and capped the port and it runs much better. I think I still feel a small miss but almost imperceptible.

I need someone to help me through the rest of the diagnostics. I am wondering if I need to replace my vac can on the distributor (bad diaphragm maybe). I'll be putting a vac pump on it to see next when I get home.

Let me know what I've left out in my signature.

Thanks.

 

[350runner]

Perfect example. You need to limit the amount of vac advance via http://m.summitracing.com/parts/crn-99619-1 or something like.... while you're at it I'd get one of these. http://m.summitracing.com/parts/acc-31035
This will allow vac advance down to 5 inches. And will be even better than your current can. Limit the vac advance to 8 or 10 degrees and take it back out for a spin

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[MadOgre]

What is your base timing ?

 

[73 C10]

The timing is at 12 and with vac straight up. I guess that would be around 24. How much should the va add?

Update:

I checked the va with a vac pump. Found good va can, leaky hose.
I replaced the hose. Still runs bad with vacuum. I realized the trans and brake booster were connected at the #8 runner and if leaking would lean out 8. I found a leak at the hose between the t and the auto trans hard line. I replaced the hose and connected it back to the carb this time. It seems better to lean out everything a little then #8 a lot. I capped off the runner port. I also checked the brake booster check valve and line. Verified good. I connected the va to the timed port to start off. Not much better result. I connected the va to the manifold vac on the carb and it was pretty good.

 

[73 C10]

Hey 350runner,

Would I still benefit from va limiter you think? See my signature for my setup.

 

[SkinnyG]

This is my very simple vacuum advance limiter. Just lengthen the slot more to get more timing. I have mine set at 12° vacuum advance with no EGR.

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[73 C10]

I like it I can handle that. I've seen a tab brazed on too. Good ideas. I've got stock weights I think. A little rusty. Hit with WD40. If my base timing sounds best at 14 btdc, how should the va and mechanical be set?

Like: 14+12(limited)+20=46?

 

[350runner]

This is my very simple vacuum advance limiter. Just lengthen the slot more to get more timing. I have mine set at 12° vacuum advance with no EGR.

You must be registered for see images attach

This^^^ is exactly how I have mine setup.

I like it I can handle that. I've seen a tab brazed on too. Good ideas. I've got stock weights I think. A little rusty. Hit with WD40. If my base timing sounds best at 14 btdc, how should the va and mechanical be set?

Like: 14+12(limited)+20=46?

Google ignitionman better known as Dave Ray. This is the only source of timing an engine I follow. He makes small body hei distributors and really knows his this stuff. If you really want to unleash the beast follow his timing setup bud.

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[350runner]

Most folk don't know what having 10 or 12 initial 22 degrees of mechanical + 8 or 10 vac does when you floor it. With some medium springs... Omg

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[350runner]

You must be registered for see images

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Dang double post

 

[350runner]

I like it I can handle that. I've seen a tab brazed on too. Good ideas. I've got stock weights I think. A little rusty. Hit with WD40. If my base timing sounds best at 14 btdc, how should the va and mechanical be set?

Like: 14+12(limited)+20=46?

These are the ticket

You must be registered for see images

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[rich weyand]

350runner, what's your total timing curve, when speccing the vacuum advance in crankshaft degrees? Are you running 8 or 10 camshaft degrees of vacuum advance, or 8 or 10 crankshaft degrees of vacuum advance?

(Stock HEI is 7.5 camshaft degrees, which is 15 crankshaft degrees.)

 

[350runner]

Threw that stock esc away and got a skip white hei... total 40 degrees all in by 2600 rpm wouldn't have it any other way bud. If ya got a stock or close to cam Dave's timing setup is the way to go. I see most out there saying 50+ , but I bet if they allowed more mechanical they'd be like wow. I use the K.I.S.S. method and don't try and sound all technical so simple folk c can understand

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[rich weyand]

I looked at the Skip White stuff, but some people report issues.
http://67-72chevytrucks.com/vboard/showthread.php?t=417170

Just wanted to know how you were specifying the vacuum advance. Most are in camshaft degrees, which means you are running 33* advance at rpm with your foot in it, and about 51 degrees at rpm in cruise.

 

[350runner]

I looked at the Skip White stuff, but some people report issues.
http://67-72chevytrucks.com/vboard/showthread.php?t=417170

Just wanted to know how you were specifying the vacuum advance. Most are in camshaft degrees, which means you are running 33* advance at rpm with your foot in it, and about 51 degrees at rpm in cruise.

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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