SU Carbs

[dan_2k_uk]

to explain the reason for moving it.

if you leave it that side when you set your timing at Rickover you will already be in a state if advance. when you rev the engine there won't be enough advance travel in the mechanism leading to poor top end performance.

[djc]

Thanks Dan, understand all that, nice n clear. Just chasing Richard re mani but he is a bit snowed just now. I'll sort this advance port, cable mounting for throttle & choke, and get me a BDL... ready for the big day.

[djc]

(There's a question in here honest )
Just got my modded manifold from Richard (and a rebuilt Tbox... another story). Awaiting the main gasket, will make one for carb>manifold. SO, before I start drilling holes in my 44 - on this whole issue of vac advance I got confused again. In the how-to guide Nigel Head says his vac take-off is airbox side of butterfly (he actually moved his to put it there). Mine is there already (do 44s vary in this respect?).
So I went back to the beginning of this thread and found Scott's links re the issues. The Zukikrawlers thread is interesting - some guys deleting vac advance altogether and modding the dizzy to get more mech advance.
How about this (lifted from the Zuke thread:)

It's very easy to hook up, just plug the vac line in to any available port on the manifold. If there isn't one, make one. Tap for an 1/8" pipe nipple for a vac line, and hook it up.

Yes, go for an unported vac source. you even tee the vac brake booster line.

Yes you can go too far. If it pings during the initial tip in of the throttle, limit the movement of the vac can linkage.

Ideally, you want the mechanical and initial timing for best WOT power, then add vac advance for low throttle opening response. Properly set up, you'll think the motor has been rebuilt if you haven't been running any vac advance. At partial throttle anyway. WOT response or feel won't chance since the vac advance is gone.

Not running vac advance is giving up throttle response and fuel efficiency.

Has anyone tried this - porting off manifold?? Strikes me as a very good place to put it and in the carb body near butterfly (whichever side) woulod be less efficient or responsive.
My problem is I can't go drilling holes anywhere til I properly understand... just not possible

p.s. this bloke seems handy http://chevellestuff.net/tech/articles/ ... nifold.htm

[twiss]

If your vac advance is already on the carb/filter side of the butterfly you don't need to do anything with it...

[ScottieJ]

If your vac advance is already on the carb/filter side of the butterfly you don't need to do anything with it...

In the pic posted it's on the inlet manifold side of the butterfly?

[twiss]

Oh yeah, confused me as he said in the post above that its on the other side... when the picture says otherwise

I was thinking about sorting my vac advance but at the minute I just run a couple of extra degrees of static advance.
I did think in the past about using a spacer like this (with vac takeoff) but it would have to fit between the carb and the air filter



Note: Pictured spacer will NOT fit, just using it as an example

[djc]

Ah yes - see how confused I got. I'll get it moved t'other side then. So Twiss is running without vac but 2 deg more static. I'll get this done and in the process get to look closely at what goes on, I gather the vac is there for lower rev pick-up, and then mech advance takes over anyway.
Has anyone done an electronic conversion of the dizzy by the way?
Whatever Happens with my SU it must be better than the old claggy Aisin, which performs badly every day, but never the same sort of bad

[ScottieJ]

Your dizzy should already be electronic? Only the 410 had points from the factory.

[G340UTT]

I have a 410 which I have an SU hif38 on. As per the beginning of this post I've installed the correct needle, and it seems to be running fine, but what's s rough setting for the mixture screw? Just to see if I'm about right, as I cannot get the engine to respond as described when the mixtures good, I.e lift piston slighty, revs rise briefly then fall again, I always get the revs plummeting, either way with the screw rich or lean. If I richen it up, the engine runs crap, hardly starts etc if I lean it out the engines mid range is terrible, hardly starts ( unless you start with choke ), and cuts out loads.

Carb is clean, new needle, float height is good. Piston, dashpot oil etc all good.

As said engine seem okay, so I assume it's right. But it concerns me I'm not getting the described response

[Anton]

Re Vac advance, I also looked through Anton's build as there was a fair bit there.