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Dual 40IDF - SVDA 034 Vacuum source?

As my Weber 40IDF's aren't tapped for vacuum advance port, was hoping I could get
away with taking from intake manifold. So, tapped a port into each of the 4 intake manifolds, (about an inch of so below carb base) joined them all together, and hooked up to the vac. advance on SVDA 034 dist.

Results are great under accel, and steady cruise, but deceleration and I get 'pop corn popping' that sounds like too lean, or timing's off.

Did set the timing per new dist. install instructions 30 - 32 deg. BTDC @ 3200 rpm w/vac. hose disconnected & plugged.

Says dist. needs min. of 8 inches vac, checked & between 8 - 12, but needle was bouncing instead of steady, which brings me to wondering if I should have tapped a vac. port into the carb. And if so, looks like I don't have the carbs with the provision for vac. advance port, (IDF-XE I believe) but there are what are labeled vac. ports next to the mixture screws. Should I use those instead?

Or am I barking up the wrong tree?

Engine's just rebuilt, new top end, pistons & jugs.

Thanks in advance for any ideas.

p2
Old 08-01-2014, 10:34 AM
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In the beginning, many years ago, vacuum advance was used so that the timing would be a bit retarded to help engines get started and then the vacuum would kick in and timing would advance and be at a normal amount. As RPMs increased the mechanical advance would cause the total timing to get to what the maximum should be. Having both a nearly stock 1974 2L with Webers and several hot rodded big four race engines with Webers, we never used any vacuum advance at all since as you have found out getting a nice even vacuum signal is nearly impossible with a type four engine. I would suggest plugging the various places you have and just run mechanical advance set to what the specs call for.
Old 08-01-2014, 10:52 AM
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King Broinyo
 
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John is correct here. +1
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Old 08-01-2014, 03:54 PM
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Just to be clear...no vac. advance hooked up?

Had heard good things about the SVDA 034 used w/dual IDF's from stand point of better performance, eliminates points and better all around than just straight mech. advance like a 009 which I was replacing.

So just block off vac. taps from intake runners, and just go with mech. advance?

Does the mechanical adv. have to overcome any resistance from the then unused vacuum diaphragm that would effect timing? Or am I over thinking this?

Thanks,

p2
Old 08-02-2014, 09:59 AM
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Yes, you are over thinking this. Do not plug the ports on the vacuum advance/retard pot so the mechanical advance will not have any resistance. In a race engine all you really care about is total advance and when it kicks in. For a street engine, the advance curve is somewhat important but generally not worth any extra $$$$ for a special distributor. A 009 will work just fine if all you want is total advance.

Last edited by John Rogers; 08-02-2014 at 10:39 AM..
Old 08-02-2014, 10:35 AM
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I have 40 mm IDF's on my 1910 cc engine (34 mm venturi's and 135 main jets if memory serves along with a cam and a 009 with solid state innards and a Bosch Blue coil. . I have no vacuum advance and my engine runs strong and has good torque.

Larry Steckel
1971 Porsche 914
Old 08-03-2014, 02:40 PM
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034 Dist and 40 IDF Carbs

There are 2 vacuum ports on each 40 IDF carb

But you cannot hook the vacuum advance hose directly to the manifold as it will have full advance. The hose needs to be ON the carb and below the throttle plates.

Green circle is the Port for vacuum Remove the tiny screw (1 screw for one hose)
Old 08-13-2014, 08:06 PM
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O.k., now I'm confused, haberman...

And I would like to understand.

So, on that photo, there's the two screws in red circles,
and green circle showing vac. tap (I assume). And which
I'd need to drill and tap on my carbs.

Is that a vac. source from both throats? Or just one?
If you're with a dual carb set up, would you take vac.
from both carbs, 'y' together and plug in to distributor
vac, or is just one sufficient?

And (sorry if I'm a bit thick on this) as far as the tiny
screws, 'Remove the tiny screw (1 screw for one hose)'

So, just take out one of the screws circled in red? Just
wondering why there are 2 and only one vac. port?

As I've still got the old 009, would be interested in a bit
of comparo between the two. As I was lead to believe the
SVDA set up would eliminate the slight bog on acceleration.

But I've been led to believe before.

Thanks for your time and patience.

p2
Old 08-13-2014, 08:34 PM
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Vacuum port

The Green circle with the tube had a tiny screw in it from the factory
in the picture that screw has been removed in order to hook the vac hose up.

The 2 screws circled in red are called 'blanking screws' these are drillings when the carbs were built. (Not For Vacuum Connections)

how about posting a picture of your carb from the side.

Please disregard what I said about 2 Vacuum ports per carb. only 1 per carb
Old 08-15-2014, 02:38 PM
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Hey thanks, guess I'm

just going to run with no vac. as my IDF's don't have a provision for vac. adv. take off, apparently.

Thanks for the input.

p2
Old 08-20-2014, 08:39 PM
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Synapse Synchronic Wastegate Barbed Brass Port Fittings - M4 x 4mm Hose

Old 08-20-2014, 10:07 PM
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So...tap into those, huh?

Thought those screws were for something else. But hey, I'll give a shot and
hopefully be good to go.

I take it once I've obtained the nipples you linked to, join all 4, step down/combine
into single hose and attach to vac. adv. on dist. and off we go.

Thanks for the help.

p2
Old 08-23-2014, 11:35 AM
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Old 08-23-2014, 11:46 AM
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