To vacuum advance or to not to vacuum advance?????

run the vacuum on the street,if its not a wild cammed thing it wont need regraphing.

Keep the vac advance, it helps fuel economy heaps, it takes a fairly wild cam to make it worth taking it off. If its causing drama send the dizzy off to get regraphed ( which you should do any way) and they can fine tune the advance side of it as well ( they are adjustable) even though they don't look like they can be adjusted

If you're running a red 179 in an FJ (looking at your profile)they obviously don't know much about real cars, particularly if they can't explain what it does to take it off! Did they ask how you use your car? Take it back and ask them to set it up properly or get your money back.

i.e. From your description of how you use your car, I'd say you should use it, you said you use your car for towing which is probably one time when it is most useful!

You're pretty close in your assumption of what the vac advance does. But if it is a properly setup pre pollution car, vac advance is added to the mechanical advance and the initial setting. Optimum total advance = optimum performance =less fuel, vac advance uses ported vacuum from the carby not full manifold vacuum.

The air velocity in the carby is what provides the vacuum. Under load (eg when towing) when you plant and open the throttle this means vacuum drops off and your total advance drops this also allows you to have maximum initial advance but drops it under load to help stop your engine pinging, i.e. less air velocity = leaner mixture (other than the initial pumped fuel)= need less advance or we go ping.

Auto's and manuals use different ports, autos draw from under the throttle so they get some vac advance at idle and closed throttle while cruising, this means you need less throttle opening and use less fuel. Manuals idle slower and have little or no vac advance at idle. Under load the effect of reducing total advance works the same for both in preventing pinging.

Think of it as one part of a basic engine management computer (mech advance , cam and and carby being the other parts). (Crippled vac advance setups was one reason HX pollution red engines performed like crap even though they were basically unchanged otherwise.)

PS This is only a rough description it is a little more complicated and I'm only an amatuer who has tuned his own red motors for 30 years, I'd never let a mechanic under 50 touch one unless he had the passion. (maybe if he was a Dave)

Thanks guys, it goes back on and scratch that dyno operator!

Should have put some specs up I suppose, its basically about XU-1 spec - triple 1.75 SUs, Stage 3 YT head (we think) extractors, and a hydraulic 35/75 cam with 287 duration.

I must say the fuel economy went from pretty good at about 30mpg to more like 20mpg (not towing) but I also went from 2.78 diff to 3.36 diff at about the same time so wasn't sure which was causing the biggest difference! Fuel economy isn't so much a problem other than the limited range the small tank gives ...

Anyway, we'll see how we go. I have a local guy who is magic with the triples and really dont think I'll bother with the dyno again - he seems to get them running great.

Thanks again guys.

i know the lower diff ratio is the reason for more fuel usage,it stands to reason,refitting the vacuum advance will help it get better.

For Street use, where you're constantly driving away from Traffic lights and Stop Signs, you definitely want the Vacuum Advance connected or every other Car on the Road is going to run over the top of you.