vacuum advance pipe connection on SU's V8

On my lightweight with a 3.5V8 on SU's, the vacuum advance pipe connects to the capsule on the dizzy, on the opposite side of the capsule from the dizzy (if that makes sense - so the vacuum is pulling the advance lever out of the dizzy body). The other side of the capsule has a small vent to atmosphere. Sounds a lot simpler than the Solex setup.

AC.

Thanks alot Andrew, that's kind of what I thought (and makes perfect sense!), does yours have this delay device (black cylinder about 1" diameter) in line in the tube from carbs to the capsule on the dizzy? Good to know also that the other pipe can just vent to atmosphere, I could never work out why 'both' sides of the dizzy capsule were connected to the solex carbs / manifold.

Andrew

No problem. There's no delay device - just the pipe from manifold to capsule. My V8 is ex-Range Rover with a manual box, the setup might depend a bit where the engine was original fitted.

AC.

In message , Andrew Cleland writes

My Strombergs had that 'delay' unit fitted and a switch/valve thing. The idea was that under certain conditions - engine idle I think - the ignition was retarded but under all other conditions it worked as normal by advancing the timing. Change it for a 'single ended capsule' and you have to rip all that stuff off anyway. My vacuum pipe is taken from the top of the inlet manifold, the one on the front of the manifold is blanked off. Not sure whether it's right or wrong but that's what I have.

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Richard

Thanks Andy, that makes sense. I put it all back together yesterday, and found I had to connect the pipe to the opposite side of the capsule than Andrew C, so it pulls the capsule in towards the dizzy. The Engine fired up first turn with the new SU's so I was impressed! Today I will take for a road test and see what happens.

Andrew T

On or around Wed, 19 Nov 2008 00:58:05 -0800 (PST), "Andrew T." enlightened us thusly:

it delays the application of vacuum advance, to reduce pinking.

The other pipe if fitted was a vacuum retard. mostly, they don't seem to have this.

It'll be a pig. You'll need to reset the static timing, and then put the vacuum hose onto the side of the capsule away from the dizzy.

Hmmm, that's a little odd but possibly your dizzy has a different advance curve (or even mechanism) due to originally having both advance and retard mechanisms. It might be worth being a little careful to check that the engine doesn't get too much advance at some point in the curve with your current single-pipe setup.

AC.

In message , Andrew Cleland writes

That's the way I replaced mine so the capsule pulls with the vacuum so advancing the timing. Whether the connection on the dizzy side needs blanking off or perhaps partially blanking off to stop rubbish being drawn in I'm not sure ...

Don't blank off the retard side of the dizzy vacuum or I think it stops it advancing, as the diaphragm can't "breathe" behind it.

On the old Strombergs the advance and retard ports were "timed" by the throttle butterfly - at idle the advance port was on the atmospheric side of butterfly and the retard port was exposed to engine vacuum. As soon as the throttle started to open it moved across the ports which put the vacuum on the advance port and atmospheric on the retard. This was achieved by having one port at the top of the venturi and one at the bottom.

I'm not sure why the retard pipe was necessary in the first place, but on my low compression engine, after I put a new Weber 500 on it, I couldn't get the idle down low enough without retarding the dizzy (no, there were no air leaks..) I ended up putting a vacuum switch from Radio Spares (like a microswitch but pneumatic) on the throttle arm of the carb which switched the engine vac to the retard on the dizzy at idle, which meant I could put the static timing back where it should be.

I think the vac advance and retard dizzies were only fitted to the low comp engines? Now I've rebuilt the engine to high compression spec and I don't need the vac retard to get the idle speed down - perhaps the extra compression gives the engine more "resistance" to overcome at idle?

Andy Fox

Hi all, Thanks for all the info, it is interesting to hear how the 2 pipe setup works (Thanks Andy F). Well I took it out yesterday and it seems to go very well, but I still have the problem on long up-hills (starts to splutter + loose power etc) - see my previous thread re possible fuel starvation etc. The fitting of the SU's was a possible step forward in curing the problem. The engine runs much smoother with the SU's.

Next step is trying a different fuel pump (facet) rather than the in tank pump it has now. - do you think I can get away with putting the facet pump "in-line" leaving the in tank pump fitted and running....

Cheers, Andrew

They always do - Strombergs are the Devil's carbs!

If the restriction in flow is the in-tank pump, then it'll still restrict the flow even with another pump in-line. Take the original pump out and check the inlet filter strainer isn't half-blocked, if it's ok fit a restrictor in the return line up near the engine so that the carbs have half a chance to take the fuel instead of it being returned to the tank. I had to do this on my own vehicle some years back when it had a 3.9 with SU's in it. From memory, I made the restrictor from a small piece of brass which was a tight fit into the pipe and had a 2.5mm hole bored in it. Badger.

Hi Badger, the only reason I wanted to put them in-line is so I didn't have to drop the tank to remove the pump and manufacture a pickup pipe for the facet to use. The in tank pump is new and clean but of course I don't know if it is good for the job. The restrictor is a good idea and easy to do, so thanks, I will try this next. When I am confident I can make it up the hills on the way, I will be visiting you to get the SU's set up properly and to check out the ignition etc. I'll give you a call...

Cheers, Andrew

It would be better to harness the loose power and then you would not lose power. ;-)

- see my previous thread re possible

My old 'C' reg ran beautifully on Strombergs and 17 mpg locally with 22 mpg motorway running.

A mate of mine had a loose knot in the return pipe, a bit Heath Robinson but it worked. :-)

Martin

hehe, OK, you got me there.... :-)

Good to know others had to do something similar.