Got my truck running... sounds like a real beast. May drive it around the neighborhood tomorrow. But I've got a question. My vacuum advance get's it signal from the #4 piston intake runner. With it receiving a signal from only one piston will I have problems with the ignition advance? When it's running there's a loud ticking coming from the advance diaphram coninciding with the vacuum pulse of the cylinder. If this is a problem is there a mechanical-only advance distributor available for a-series?

I don't know for sure, but usually vacuum is taken:

1. From the ported vacuum on the carb (only has vacuum above idle).

2. From the plenum of the intake manifold. If you do this, you must disconnect the hose before timing the engine

I've seen "balance tubes" going from one cylinder to another. Maybe you could try that, and tee the advanced to both cylinders to even it out?

sounds pretty dodgey to me,

id say there would be a better way to do it, are you using a stock manifold and carby?

it should recieve signal from all four pistons

actually i think i know what you are using, there is a fitting with a big tube for the brake booster and a small for vacuum advance, both from te number 4 inlet

i am using the brake booster one but not the vacuum one, id like to plug that and use another outlet on the manifold for the booster (before the seperation to each piston, there is outlet on the passenger side just below where the carb bolts down)

but at the moment as i have a 32/36 weber, it has an outlet for the vacuum advance on the bottom of it and i am using that for the advance

oh yeah congrats on getting it running!!!

Quote:
Tap into each runner and install a vacuum canister that all 4 lines run into. Then run a single line from the canister to your dizzy.

no id think that would be much harder than necessary, it only needs one tap appropriatly placed before the seperation to each cylinder

From my experience with side draught carbs. I have never run vacuum advance to the dizzy. Dial in your dizzy to required specs, The only suggestion i could make, well two suggestions is 1.re-graph the dizzy and 2. modify the springs / weights of the mechanical advance to match your modified CAM.
To my understanding vacuum advance essentially only plays part during idle and near idle until mechanical advance takes over.

Cheers,

Benny

Thanks for all the replies. If it doesn't do much except for idle/near idle advance then it'll probably be okay for now. I'll have to research where I can send the dizzy in Japan to get it worked out. What plugs are you guys with high compression, sidedrafts, cam and headwork running?

vaccuum advance does a lot. This has been discussed several times in this forum.

Mechanical advance comes into play at higher revs. Vaccuum advance does nothing at full throttle. But at part throttle it advances the timing. You do want the most timing, don't you?

Ddgonzal is, as usual, 100% correct.

If you draw vacuum for the distributer direct from the manifold, you get full vacuum advance at idle, assuming that it actually develops vacuum at idle. [I dont know your cam specs.] This is BAD

If this is a road engine, then you will want to have the vacuum advance wotking in an attempt to increase operational efficiencies at part throttle, like in cruise mode. The ONLY way to get the correct vacuum signal is to use the ported vacuum fitting on the / a carb.[It does have one doesn't it?]

This port is just upstream of the throttle plate, so that when the plate is at idle, this port sees NO vacuum at all. As the throttle is opened, as in full throttle, there isn't enough vacuum to suck fizzy drink up a straw, so you get mechanical advance only.
Once you are up to cruise speed, the throttle is reduced & this port can see some suction. This results in more acvance & increased eficiencies. Read this as, "improved fuel consumption figures" which is what you want when just cruisin'
Stab the pedal, throtle opens, vacuum vanishes & ignition timing reverts to centrifugal control only, It works a treat, but manifold vacuum at idle messes with your traffic driveability & thats a pain.
Chris