I have read conflicting repots on where to set the timing for a vaccum and mechanical advance dizzy (svda)

I have read that timing (unknown engine with degree wheel and *probably* standard bus cam -t1 1600 in '75 kombi with 34 pict3 carb) should be set at 32 deg total mechanical advance with the vacuum hose plugged.

This then lets the vacuum advance the dizzy more than 32 deg total advance at high revs, with a good vacuum signal. (getting close to 40 deg) I have also read this is bad.

If I retard it to 32 deg total advance it has a big flat spot and idles too low

At 32 deg mech advance only (vacuum blocked) it ends up static @ tdc. Runs well with heaps of grunt (yeah who am I kidding its a 1600.....) cannot hear pinging. Have yet to run for > 15min on the road to see how hot it gets (oil temp)



Discussion welcome

kkk

I'm no expert, but I believe that the TOTAL advance should be 30-32 degrees at 3000rpm, by which time the centrifugal advance should be all in....

You Had it right the first time.
time it to the 32 deg maximum mech advance with vaccum plugged then reconnect the vacuum.
This will only give vac advance with small throttle openings siuch as revving the engine in your drive or cruising gently.
Jeff

Gee I find this topic interesting!
Setting to a certain no. of degrees for EVERY engine of that type is assuming they all are the same & they are not. There are varying amounts of wear to consider as well as the type of driving that is done etc etc.
I set mine statically & then put my strobe light & tools on the front seat & go for a drive. I go to a long climbing road & check for pinging while going up. If there is none, I advance it a few degrees & try again etc etc. When I get pinging, I back it off to the last setting & confirm that it's happy.
Am I doing anything wrong??

geodan, that is actually a very good way of doing it.
I used to have an old Jaguar which had a knurled adjuster wheel on the dissy which allowed you to do the fine adjustment easily after road testing.
Jeff

Only that you are baseing it on being able to hear the pinging

That's true blue, but I do it the same way.

This procedure is what is actually recommended in my old MG workshop manuals.
Blue, I hear you but I am not advocating wholesale changes. My point is that if X degrees of advance is OK for one engine an identical engine running different petrol or at a higher altitude & travelling up & down hills may go better at X+ or - 2 or 3 degrees & this procedure helps pin it down.
Am I correct in assuming you need as much advance as possible short of causing pre-ignition ie pinging?

Jeffh- what model Cat? I've owned heaps from 4.2litre XJ6's right down to a Mk5 & even a Mk4-which was capable of 90MPH & with only Tattslotto (ie mechanical) brakes to pull it up!