Giving Up On Vacuum Advance Options

[Ansbacher]

Car = '74 2.0 Liter, Dual Dellorto Carbs

For years I have been 'adequately" running an 009 mechanical only distributor. Finally took the pervasive advice out there to go with a vacuum advance dizzy from a 1.8L 914. Since only one of my Dellorto carbs had an existing vacuum port (ported type), I had to drill a port in my other one (no problem there). I used good quality anti-pulse valves in the lines and measured a maximum vacuum of 12 inches of mercury with partial throttle.

Installed the 1.8 dizzy and set the timing, first without the vacuum lines attached. To satisfy my usual 30-32 degrees at 3500 RPM, the idle timing had to be at about 5-6 degrees (quite low for my setup which is happier at about 10 degrees. When I attached the vacuum lines my timing at 3500 RPM went sky high into the 40s. This seems way too high. Is this normal? Overall, I found the car to run better without the vacuum attached and the carbs plugged off.

Am I doing something wrong here? I don't like the numbers I am getting. Everyone said this was the way to go with carbs, but I am not seeing results. Advice appreciated.

Ansbacher

[Red72]

Jumping in here, and I'm sorry to hijack it somewhat, but this seems to at least be an active dizzy thread.

I'm fairly new to distributors, and I'm looking to tweak the curve with the springs and stops on my pertronix unit on my 1.7l engine. I'm looking to combine two different spring weights in order to control the initial (off idle), and total advance. The question I have is, will I still get full advance if I limit the advance on a LIGHT spring to something like 6 degrees above initial, and then allow the HEAVY spring to go all the way to 20 degrees advance, resulting in something like 28 full advance?

Thinking that this will bring advance on early, but then climb more slowly up to 3500rpm. This seems to more closely match the curves of non-vacuum, non-009 units.

I realize the answer here seems to be 'get the 123 unit', but the dollars for that isn't in the cards right now.

Thanks.

[tmessenger]

I went through this with a Triumph TR3 a couple of years ago, the factory distributor springs were NA and the old springs were shot. I modified other springs to work and it was just a process of trial and error to get the curve right. I used an electronic inductive tachometer to dial in different engine speeds and then checked the advance at the crank with a timing light. It took a while but I tweaked the springs until the mechanical advance curve was correct.

The only other option I know of is to find someone that has an old sun distributor machine to set up the mechanical advance.

Tim

Jumping in here, and I'm sorry to hijack it somewhat, but this seems to at least be an active dizzy thread.

I'm fairly new to distributors, and I'm looking to tweak the curve with the springs and stops on my pertronix unit on my 1.7l engine. I'm looking to combine two different spring weights in order to control the initial (off idle), and total advance. The question I have is, will I still get full advance if I limit the advance on a LIGHT spring to something like 6 degrees above initial, and then allow the HEAVY spring to go all the way to 20 degrees advance, resulting in something like 28 full advance?

Thinking that this will bring advance on early, but then climb more slowly up to 3500rpm. This seems to more closely match the curves of non-vacuum, non-009 units.

I realize the answer here seems to be 'get the 123 unit', but the dollars for that isn't in the cards right now.

Thanks.