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Dizzy vac unit gone bad?


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#1 Bruiser

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Posted 25 November 2021 - 05:24 PM

Can I bother any of you geniuses for a bit of a hand?

Been buggering around for a while getting my 202's idle and off-idle sharp.
Recently put the choke back on my (choke towerless 4 barrel holley) thinking
it'd be better than revving it up to get up to temp.
Choke lever has been super touchy as in barely running or taking winding up,
being difficult to getting it to sit at 11/1200 or so.

Unplugged vac advance hose, plugged up carby outlet, timing light tells me
I have 16°ish at idle, 32°ish all in.

Operating vac hose orally, timing shows 45°ish. !!!

That could'nt be normal, could it?
Do the canister diaphragms clap out?
I've seen 6° stickers on them before, how much are they supposed to add?

Cheers lads

And all sucking on hoses and pipe gags welcome

#2 claysummers

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Posted 25 November 2021 - 05:27 PM

6 degrees refers to the static setting I reckon.

early Holden nut

#3 claysummers

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Posted 25 November 2021 - 05:42 PM

I guess it depends on what cam you are using, but for stockish setup 16degrees is a lot, and 32 not much at high revs. I’ve got a box of points dizzys if you need parts. I always set the static timing by ear. Advance until it pinks under load.


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#4 I'm a Red Motor fiend

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Posted 25 November 2021 - 06:06 PM

I've never used vac advance with big cams. Why not just delete it?

#5 Bruiser

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Posted 25 November 2021 - 06:07 PM

Thanks for the offer Clay, and the help too.
My cam is the pc206 dynotec, 1 up from yours. HX xu1 roughly.
Been down that road years ago stopping every 600 metres to knock dizzy up till she pings.
These days I think it probably ended up too high even not pinging (audibly)
Using a timing light these days
Just been out mythbustering under the bonnet, ported vacuum at 1000rpm, about .5". timing 20°
So bugger all vacuum really, just like it's supposed to be.
Upping revs by 300 did pull up to 5" though.
Had carb off again this arvo freeing up sticky throttle plates
I might of accidentally fixed my problem by adjusting primary/secondary position for idle.
I do know that the primary throttle plate can put vacuum to the outlet if opened too much

My mighty sucker can get 17" on the same gauge, but I wasn't trying that hard yesterday.

Seems better now, anyway

If there's anything i've missed please tune me in


Thanks

#6 Bruiser

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Posted 25 November 2021 - 06:18 PM

Hi Adam

Never did have it connected for years, it's always run great
Always drank a lot, though. Built it in 2004, learnt a fair bit about tuning
since then, still learning, too.
The idea of the part throttle/cruise advance business makes sense to me,
thinking it might help the economy a bit too
When I want to bean it, vac goes and back to mechanical timing again.

My cam is only half the size of yours, do you reckon I shouldn't bother?

#7 I'm a Red Motor fiend

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Posted 25 November 2021 - 06:45 PM

I couldn't remember your cam specs.
What you say is true, there are benefits running vac advance.
45 degrees sounds about right, remember this is not under full load only at light throttle where the vacuum is greater so it won't ping.
I would persist with it perhaps.

#8 Heath

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Posted 26 November 2021 - 08:25 AM

Why would you ever not want vacuum advance?

(we're talking street cars here)



#9 Bruiser

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Posted 27 November 2021 - 01:56 PM

Thanks for the responses, fellas.

Was referring to the car drinking a lot,though I have my moments.
Yeah, Heath, it's supposed to help with exactly that, being a
quickish car that would honestly be driven sensibly most of the time.

So I'm not going crazy, then?
Just read that throttling off down a hill could produce up to 25" of vac,
so the timing would then do a leap up round the 45° I saw.

Is it operating as it should be?




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