738 replies to this topic

[Bruiser]

Been out to shed to satisfy my own curiosity,
Here’s what goes on with the vacuum ports


The nipple for the dizz vac hose
 IMG_0777.jpeg   277.66K   5 downloads

Comes out here, just upstream of the butterfly when closed
 IMG_0778.jpeg   176K   4 downloads

Just to compare, Holley does it the same way
 IMG_0779.jpeg   160.65K   5 downloads

It doesn’t take much throttle to expose those holes, with the Holley there can be some vacuum
if the blades are too far open at idle.
Disconnecting yours would eliminate the possibility that is happening to you, Clay.
Doubtful, but you never know I suppose.

Googling last night about how much vacuum pull it provides and when, I came across this opinion
on the jag lovers forum:
Question - “Vacuum measurement at su carb”

“The ported vacuum on the front carb should be atmospheric pressure at idle and atmospheric pressure anytime the throttle is open more than about halfway. You should have some vacuum at that port if you raise the RPM to about 3000.”

Don’t know if the guy who made that post is a guru or not, but the 3000rpm is a decent coincidence

[yel327]

By upstream Bruce do you mean engine side? That Holley is manifold vacuum, is the SU where the paperclip is poking out the engine side? If so that is manifold vacuum too. A ported vacuum source sits above the throttle plate.

 

Some people swear by full manifold vacuum at idle for a manual, but as far as I am aware GM have never done that, always ported for a manual and manifold for an auto. I guess it depends upon how the car is setup, when and how it wants advance etc.

[claysummers]

Thanks Bruce for doing the homework for your lazy mate.

I will give it ago. While you are technically correct Byron, it isn’t pulling any advance at idle, like my idea of manifold vacuum fed autos.


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[Bruiser]

Sorry Byron, by upstream I meant above the throttle blade, air cleaner side, SU and my Holley both have the same arrangement
just above the blade, that’s the ported vac one. Some Holleys have a knipple in the baseplate for manifold vac.
That Holley opening in the picture leads back directly to the outlet on the upper side of the metering block.
The manifold vac vs ported vac debate is a hot one on any forum you can find it on,
people on both sides of the fence swearing one is better than the other.
I tried it from the manifold once for half a minute and it sucked. For me.
(haha, sucked)

No worries Clay, most queries around here send me scurrying off to have a Google if I want to know
for myself. Checking out these things compared to what I think I know usually leads to something
more in-depth and if it could be at all helpful I will post it up here so I look like a genius.
At least I learn something

Did you win any treasures at Dudley’s auction this time around?
EK guards for $1350?

[yel327]

I think most of those discussions are ill informed, I've seen a few of them! Whatever they all state for non-standard engines, it is a straight fact that from the 60's at least manuals used ported vacuum and autos used full manifold vacuum. At least until the anti-pollution stuff (basically like ADR27A we got here) arrived, then it became a dog's breakfast.

[claysummers]

No tresures, mate gif a single FB guard for $165. The rest was off the planet.


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[claysummers]

I tried less advance and vacuum delete but still random pinging. So I've swapped my old distributor back in, which seems to have stopped it. I'm on the road to Bunbury at the moment and didn't bring a timing light but will use my ear. Something just isn't right about that VK EFI dissy.

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[Bruiser]

Maybe the advance springs have been swapped, or have gone soft making the mechanical advance come on quicker than factory settings?
Anyway, there will be plenty of guys at Bunbury you can bounce it off for more ideas.
Good luck and have a safe trip, and a top time

[claysummers]

It's 40 years old and worn out I say. I've advanced it a bit more, and reconnected the vacuum advance. Still no ping up to 3000 but haven't gone higher.

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[Ice]

I tried less advance and vacuum delete but still random pinging. So I've swapped my old distributor back in, which seems to have stopped it. I'm on the road to Bunbury at the moment and didn't bring a timing light but will use my ear. Something just isn't right about that VK EFI dissy.

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Hope you bring ya wet weather gear its not going to good down there next weekend 

[Bruiser]

That day you brought it up here when we had a look at it - I think I remember
that 40 year old dizzy’s weights having a little bit of slop on their pivot pins??
Maybe that is the problem ( if I didn’t dream it)
How did she go on the big drive over?

[claysummers]

Going good now Bruce. I needs 98. I still want to run a shorter curve if I can do it easily enough, so I can lift the initial advance a bit.

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[claysummers]

Well the thing made it to Bunbury with no major issues. Occasional ping on 91, which was all I could get when I filled up the jerry cans at Yalata. Averaging a lazy 26.2mpg, 91 or 98. Sitting on 100 - 110. Used 0.5 litres of oil Willunga to Bunbury.

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[Bruiser]

Found you an in depth discussion about quench on speedtalk
that might be of interest

https://www.speed-ta...pic.php?t=68699

Edited by Bruiser, 07 July 2024 - 12:06 PM.

[claysummers]

Thanks Bruce. You sure did.


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[Bruiser]

chucklechucklechuckle

[claysummers]

I am having an intermittent combustion break down, two out of the last three decent runs in the car. This has been on two separate tanks of fuel, from different local sources. It will intermittently misfire and stall when laboured and sometimes ping at higher revs when throttle is opened.


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[claysummers]

Pulled the plugs
If anything a bit lean to the rear.


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[claysummers]

Also, the starter is disengaging during cranking. Sometimes not engaging. I suspect an issue with the solenoid. I have another Bosch gear reduction starter, which I will swap in.


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[warrenm]

What plug gap are you using? I generally run .035/.040" with hei, the wide plug gaps from the factory was for emissions.

[rexy]

Front at top?

If so they are progressively hotter to the rear and the bottom two straps look too hot.

[claysummers]

What plug gap are you using? I generally run .035/.040" with hei, the wide plug gaps from the factory was for emissions.

I just followed the workshop manual value 0.060” Warren, since day one this motor and hasn’t been an issue, so far. I’m not discounting the possibility it could be the spark breaking down though. I’ll try swapping the coil at some stage, once I rule out the pump. While I have them out I will recap to 40/1000”. Thanks for the input.


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[S pack]

Pulled the plugs
If anything a bit lean to the rear.


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lol, Russian made Bosch spark plugs. They are made to break down.

Get yourself some NGK plugs.
 

Edited by S pack, 07 October 2024 - 07:46 AM.

[claysummers]

That’s what I get for buying at Supercheap. May as well throw a new set of NGK in. I was sus when they brought these out.


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[Bruiser]

Those wr6 bosches are a fairly cold plug for everyday driving according to this chart

 IMG_0855.jpeg   26.65K   2 downloads

I’ve been getting away with ngk bp5es gapped at .040 for ages
with no problems I can see. They stay clean too as long as not over rich
Recommended heat range for standard engines, I think
The colder bp6 needed if worked motor is working hard
They look like this

 IMG_0856.jpeg   289.07K   3 downloads

I reckon they are still a touch too black around the outer ring
Maybe for you a hotter plug would get rid of all the soot that’s there now
I bet the .060 gap makes it hard for the spark once things get dirty