Dynamic timing a vac advance dizzy

[noddy]

Hi

I would like to dynamicaly time my van but not sure by what RPM a vac advance dizzy should be fully in.

Dizzy has 30 deg total advance, Bentley manual says to time at 0 Deg at 850 RPM.

Can anyone let me know what RPM total avance should kick in at.

Thanks all

Ian

 

[VWAIRCOOLED]

I time a vac dizzy at 7 BTDC at idle with the vac line plugged.I read somewhere that max advance happens at about 3200 rpm.When I check mine thats what I get.Thats also what they recommend to set the 009's at so I think you'll be safe aiming for max advance at 3200 rpm

 

[noddy]

thanks

 

[Joval]

What dissy is it? Some are vac only and need to be timed at 850

 

[Clarkson46]

The correct set up is determined by the dissy type. Look it up on here and it will give you the parameters.

http://www.oldvolkshome.com/ovhignbo.htm" onclick="window.open(this.href);return false;

 

[noddy]

Vac only part number 113 905 205 t.

I wanted to time to total advance to check if its over advancing. Bentley manual only shows changes in the advance curve at certain vacuum pressures. (bentley manual section 5 page 75).

This section says end of vacuum range is 75mm(2.9 in) Hg of mercury with an advance of 16-17.5 deg. Does this mean my distributor should only have a total max advance of 17.5 deg. I know some of the mech advance dizzy have up to 27 total advance or is this 19.5 deg if dissy is timed at 7.5 BTDC?

I have a suspicion that my engine has been over heating and the only thing I can put it down to is the dizzy, all tin, seals etc in place, plug look good, I have done the hold the dip stick test and its never to hot to hold.

Advice appreciated :shock:

 

[Clarkson46]

This is what the Old Volks Home says

Bus & Pickup 1969-1970 * 1600

Distributor: VW 113-905-205T, Bosch 0231 137 035 or 036
Can Use: VW 113-905-205M, Bosch 0231 137 021
Replacement: VW 111-905-205AA, Bosch 0231 137 039
Points: 01 013
Points Replacement Plate Assy: VW 111-905-227B, Bosch 1237 110 139
Condensor: 02 007 - Note: If equipped w/AC use 02 069
Rotor: 04 033
Cap: 03 010
Parts Kit (Washers, Shims & Hardware): 059-998-211, Bosch 1237 070 007
Coil: 00 015 (Blue Coil: 00 012)
Vacuum Can: 07 024 (Replacement uses 1237 121 400)
Ignition Wires: 09 001
Spark Plug: W8AC
Timing Set At:: 0deg TDC Static or @ 800-950rpm w/strobe w/vacuum hose disconnected and plugged
Advance/Retard Range: Vacuum (Advance Only): 17-19deg @ 1.3 In. Hg, 32-35deg @ 3.2 In. Hg

Ideally you want an SVDA dissy which has mechanical advance as well, give much better performance.

We have this dissy fitted to a 1641 in a '68 Bay which is what it arrived from the states with (the dissy not the 1641)

Bus & Pickup Late 1976-1978 All States, 1979 Federal * 2000

Note: This Distributor also fits Type 4 (412) 1974
Distributor: VW 021-905-205P, Bosch 0231 168 005 > 022-905-205S, 0231 170 093
Note: 0231 170 093 dist primarily used on California Late 1976-1978 and all Federal 1979 Models
Can Use:
Points: 01 011
Condensor: 02 074
Rotor: 04 033
Note: 0231 168 005 dist originally equipped with Speed Limiting Rotor 04 016 (5400rpm)
Dust Cover: 039-905-241, Bosch 1230 500 139 > 1230 500 147
Cap: 03 010
Distributor Cap Clip: 034-905-265, Bosch 1231 251 033
Parts Kit (Shims, Washers & Hardware): 059-998-211, Bosch 1237 010 007
Coil: 00 012
Vacuum Can: 07 060
Ignition Wires: 09 171
Spark Plug: W8CC
Timing Set At:: 7.5deg BTDC @ 850-950 rpm (Man Trans), 900-1000 rpm (Auto Trans) w/strobe, vacuum hose connected
Advance/Retard Range: Vacuum: 8.5-11deg Adv @ 7.9 In. Hg; Centrifugal: 8-13deg @ 1600 rpm, 20.5-24.5 @ 3400 rpm

 

[noddy]

Thanks

I think that has made me feel better, I was lead to believe that the aircooled engine did not run well beyond 27 deg total advance but looking at the figures my dizzy is within spec.

Ian

 

[Joval]

I have a 205T too, I switched back to the 009 as it was popping on overrun - I don't think it works with a 34 carb,

can't check now though as I can't get on to the samba for some reason :roll:

 

[Joval]

I think this is the right link -

http://www.thesamba.com/vw/forum/viewtopic.php?t=185095" onclick="window.open(this.href);return false;

 

[noddy]

Thanks Joval good info in that article.

 

[Joval]

What does it say about the 205T? I can't get on to the samba :lol:

 

[noddy]

This was the bit I found really usefully, it means I can check RPS v vacuum for a 30 pict 3 with a 205T.

Thanks again

Ian

 

[Joval]

Hmm, '1385' cc??

 

[noddy]

But all in by 3800 RPM at 100mm Hg, this wont change for bigger engine, or will it :?: Will a bigger engine create a bigger manifold vacuum quicker, my guess is bigger displacement creates bigger manifold vacuum at lower revs :?

 

[Clarkson46]

As I have always understood the issue of ignition advance, it is all down to the speed with which petrol burns which is a constant. So at 1000 rpm we need a level of ignition advance that fires the plug sufficiently early to ensure that the burn will have completed by the time the piston reaches TDC this way the maximum energy is transfered into the piston. As the engine revs rise the level of advance must increase so that the burn starts at the right time for maximum power delivery. This is why the SVDA dissy gives advance at low revs controlled by vacuum and as the revs rise the centrifugal advance takes over. This way the advance will remain directly proportional to engine revs, which is why it is important to ensure that the dissy is timed correctly at idle. The single vac dissy does not have the ability to advance properly at high revs and the dreaded 009 does not advance properly at low revs hence the ubiquitous flat spot.