SVDA issue

[72Hardtop]

Swapped out my less than stellar Pertronix SVDA for a new Bosch SVDA and have an issue. To start I set the engine to TDC #1 for removal of the Pertronix unit. Once out I installed the Bosch SVDA and eyeballed it close to get it started. Once bus was running I proceeded to throw the timing light on. Set it initially at 7.5 BTDC (hose off & plugged). I then rev up to approx. 3200rpm's and set for 28 * full...wait, wait...what it won't go to 28* full. Left off gas and now it doesn't fall back to 7.5* either. Reset initial...repeat same results. What gives?

Checked the vacuum advance and its free not hanging on anything (operates smoothly).

I'm guessing the centrifugal side of the distributor is hanging up. I went ahead and pulled the top half of the Bosch SVDA apart and clean it all up then removed the centrifugal advance plate/mechanism and clean the inner OD and outer OD shaft. Was dirty (black Q-tips). Lightly greased everything up and put back together. Have not installed and tested yet. Any thoughts/ideas/suggestions?

On another note I did notice how soon the Bosch vac can kicks in vs the Pertronix SVDA. I noted the following with vac gauge:

Pertronix SVDA - vac can arm begins to move at ~ 4 in and stops at 10 in (holds vac well)

Bosch SVDA - vac can arm moves right off from 0 in and finishes at 5 in ( holds vac well)

now if I can just get the centrifugal side to play well. I'd expect this from Pertronix but damn it worked except for the lack of no vacuum advance. Can't say the same for the Bosch so far.

[Ryno]

I remember with a Bosch SVDA that I had years ago, it took a little bit to get it "stretched out". I was on the phone with John @aircooled.net several times and even sent it back to him. After he ran it on his test engine through a few higher RPM cycles it worked great. YMMV.

[Amskeptic]

I pulled Bosch SVDA apart and cleaned.
Have not installed and tested yet.
Any thoughts/ideas/suggestions?

Install and test it.
Colin

[72Hardtop]

I pulled Bosch SVDA apart and cleaned.
Have not installed and tested yet.
Any thoughts/ideas/suggestions?

Install and test it.
Colin

Just finished testing. Results:

Hose off & plugged got the distributor timed close enough to start. Once started bumped it to 7.5 BTDC. Ok, everything good so far. Rev engine to ~ 3200+ RPM's and timing advances smoothly all the to 24* and stops. Release and advance goes back to 7.5 BTDC smoothly. What? Only 24 degrees? Check again same results nice and smooth up & down. Reset mixtures and idle speed set to 870-890.

Well it appears I resolved the advance hanging issue. I just set the distributor to ~ 27.5 - 28 full (hose off & plugged) idle timing settles at ~ 10.5 - 11 degrees initial. With vacuum hose on I'm seeing perhaps 4 -5 degrees vac advance if I play with the throttle around 3200-3400 RPM's. Will monitor it.

Searching around I've come across others that appear to have gone down a similar road as me. Quiet a few saw change as the distributor settled in.

Guess time will tell. At least it better than that Pertronix SVDA.

[Bleyseng]

but how does it drive? Flat spot of idle? Smooth rpms and power curve to 3500 rpms? 7.5 and 10 so what as long as it runs better.

[72Hardtop]

Took it for a short drive and it drove nicely.

[72Hardtop]

Next project...LM-2

[Amskeptic]

Next project...LM-2

Note that some distributors start life with a narrow timing range (yes, set to 28* who cares what the idle timing is?) that opens up over time.
Colin