Dual Vacuum Timing

[oldschool71]

Hi,

I have a 71 1600TP, Empi type solex pict34, Dual canister distributor

Timing set to 5Deg ATDC

with retard pipe disconnected its giving me 20Deg BTDC!! Am i right in thinking that it should be giving me 7.5Deg BTDC ?


Any help would be appreciated


Andy

 

[Dave.P]

Maybe you can find your answers here ?
http://www.vw-resource.com/vacuum_qa.html" onclick="window.open(this.href);return false;

 

[Trikky2]

Hi,

I have a 71 1600TP, Empi type solex pict34, Dual canister distributor

Timing set to 5Deg ATDC

with retard pipe disconnected its giving me 20Deg BTDC!! Am i right in thinking that it should be giving me 7.5Deg BTDC ?


Any help would be appreciated


Andy

The dual canister dissy is unusual in that it is the only one where you have to set the timing with the engine running and the pipes connected.

If you try to time this type of unit with the pipes disconnected the readings will be wrong.

That said, this type of vac canister can be used with the retard pipe disconnected, not blocked off, the corresponding port on the carb blocked off and the timing at tickover set to 7.5 BTDC.

If you are getting 20 degrees advance then you need to check both the canister and the throttle setting (there should not be any vac signal from the advance port when the engine is idling).

Back in the 1970's it was common practice to replace these double vac units with normal single ones, block off the retard port on the carb and re time to 7.5 BTDC. This was done to cure persistent hesitation and flat spots cause by the dual vac system, which had been introduced to meet a specific emission test in the US.