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SU carb vacuum port ? 120-130 1967

posted by  riverbend on  Wed Jan 4 16:17 CST 2017
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last visit: Wed Oct 22 15:29 CST 2014
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I'm working my way back towards a stock set up with this car, going back to dual SUs. The car currently has a vacuum advance on the distributor. The SUs do not have a vacuum port. Where did the distributor get the vacuum on the original set up ? Thoughts on a solution ?

Thanks

Greg







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    SU carb vacuum port ? 120-130 1967

    posted by  Phil S. on  Wed Jan 4 18:58 CST 2017
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    last visit: Fri Oct 24 13:18 CST 2014
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    I think you may have vacuum retard on the distributor, not advance. If the vacuum module faces the firewall and is offset away from the block, it's retard and you're better of leaving it disconnected. If it's offset towards the block, it's advance, but not original to a '67.








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      SU carb vacuum port ? 120-130 1967

      posted by  riverbend on  Wed Jan 4 20:58 CST 2017
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      last visit: Wed Oct 22 15:29 CST 2014
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      The vacuum module points straight back towards the firewall. The vacuum port points up and is slightly inclined towards the block. The tag on the side says VJU 4 BL 33. There may be some other letters after that, but I could not make them out reading in a mirror.

      I don't know how this distributor works but it advances with increasing rpm and total advance comes out about right. Looking in the manual, this distributor fits a B 18 A and it lists advance rather than drop in the specs.

      I still think I need a vacuum source behind the throttle plate.

      Greg







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        SU carb vacuum port ? 120-130 1967

        posted by  planetman on  Thu Jan 5 01:15 CST 2017
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        last visit: Fri Oct 24 09:29 CST 2014
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        Hello Greg,

        Your VJU 4 BL 33 distributor is from an earlier B18 engine and does have vacuum advance. FYI, the original distributor for your car was a mechanical advance distributor and did not have either vacuum advance or retard and most of the B20 distributors are vacuum retard.

        And if you want to connect the vacuum advance correctly you will need a ported vacuum fitting and the stock 1967 carburetors didn't come with 1. Vacuum retard distributor are supposed to be connected to a manifold vacuum fitting.

        The early SU HS6 rear carburetor that came on the early B18 engines did come with a ported vacuum fitting.

        If you want, I believe the fitting is still available new and you could drill a carburetor and install it.
        --
        Eric
        Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
        Torrance, CA 90502
        hiperformanceautoservice.com or oldvolvosonly.com








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          SU carb vacuum port ? 120-130 1967

          posted by  riverbend on  Thu Jan 5 07:46 CST 2017
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          last visit: Wed Oct 22 15:29 CST 2014
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          What do you think about tapping one of the holes for the secondary throttle plates (now removed) in the intake manifold and installing a fitting there ?








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            SU carb vacuum port ? 120-130 1967

            posted by  Volvo From Heck on  Thu Jan 5 10:34 CST 2017
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            last visit: Mon Oct 13 20:56 CST 2014
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            Riverbend wrote--"What do you think about tapping one of the holes for the secondary throttle plates (now removed) in the intake manifold and installing a fitting there ?"
            That would get you manifold vacuum--not ported. Ported vacuum fittings have to be located before the throttle plate--hence planetman's suggestion to drill and install a fitting. I have a rear 3-hole-with aux. throttle lever (not the one I'll take the choke lever from for you) that has the port. I'll take photos with a ruler as reference and send them to you.
            I think a Weber 32/36 (the carb you are replacing) has a ported vacuum fitting--so the distributor would have worked properly with that carb.
            You mentioned that you have good total advance--how much? It's safe to go to the mid 30's. Are you there? What is your idle--or initial timing? Distributors w/o vacuum generally get set to a range of 0-10 degrees BTDC with the mechanical advance taking it the rest of the way. I have spare mech-advance distributors. If you can find one--I'd recommend a distributor from a '75 240 along with the control box, resistor and coil. Makes a huge difference. -- Dave








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              SU carb vacuum port ? 120-130 1967

              posted by  riverbend on  Thu Jan 5 16:58 CST 2017
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              last visit: Wed Oct 22 15:29 CST 2014
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              Well, ported vacuum it is. I looked at the Weber and the vacuum port is above the throttle plate. Photos of the location for drilling and tapping would be most appreciated. I see there are a couple of undrilled bosses on the throttle bodies, are those places to drill ? It would be nice to have a flat spot to line up on.

              I'll have to check (and write down) the initial and total advance numbers but 30° or so sounds right for the total advance.


              Greg







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                SU carb vacuum port ? 120-130 1967

                posted by  Phil S. on  Thu Jan 5 18:59 CST 2017
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                last visit: Fri Oct 24 13:18 CST 2014
                [RELATED]

                Total advance without vacuum should be between 32 and 34 BTDC.

                I'll probably get an argument about this, but it's perfectly okay to hook the vac advance up to the manifold, rather than have it "ported." As soon as the throttle opens a fraction, it functions identically either way. Hooked to the manifold, you'll have full vacuum advance at idle -- which is fine as long as you set the timing with it disconnected and plugged -- but when you start to accelerate, it backs down to the same advance it would have if hooked up ported. you may even have a smoother idle with it hooked to the manifold.







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