1.9DF Vacuum advance...and retard?

[DevonAid]

Hi all

The elusive flat spot on our 1.9DF Devon (Solex carb, all standard, 130k miles) deserves another investigation. Generally 'Norma' is running well, starts well, gets (just about) enough attention with regards to maintenance, timing when last checked is OK, got us to Cornwall and back to the Big Smoke (that's London, not the van) recently without issue. Thanks to guidance on this most excellent of forums, I've looked very closely at all vacuum related pipework, distributor vacuum unit operation, and potential sources of vacuum leaks including base of carb etc, even investing in a vacuum gauge recently to double check servo hoses (although replaced this hose a while ago with new) . Alas, no 'eureka' moments as yet.

The 'poor brother' 1.9DF gets a little less attention than other models (bit less on the Wiki, Brickwerks don't seem to stock the distributor vacuum advance unit etc) so is someone able to clarify how the 'retard' function (assuming that is what it is) is supposed to operate and what to check for? Is our vacuum hose set up correctly and any other helpful observations?:

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The flat spot is significant and most noticable when pulling away from a standstill - it really is bad, so plenty of revs are needed to get away at roundabouts etc. Much less noticable when on choke (but not sure if this is due to timing change on fast idle or enriched mixture). Otherwise runs Ok, whilst considering the power output (or lack of) of the humble 1.9DF.

Any helpful comments appreciated and will hopefully inform the next stage of my investigation. Thanks in advance.

[itchyfeet]

I think the two vac pipes are advance and retard, can you suck or blow through either of them?

Some checks you can do here.

http://www.brick-yard.co.uk/VehicleSpec ... DFdata.htm" onclick="window.open(this.href);return false;

could be accelerator pump and not ignition

I think the DF vac unit is 025905271 with no suffix ( see Bigherbs post here) but best check

http://www.brick-yard.co.uk/forum/what- ... 28483.html" onclick="window.open(this.href);return false;

https://www.vwheritage.com/vw.cfm?act=v ... GB&lang=EN" onclick="window.open(this.href);return false;

[Bubble Meister]

On your photo you have two pipes coming off the dizzy vacuum chamber. I only have one on my DF!
I have the one that goes into the side of the carb - I haven't got the tapping or pipe that goes to the 4 way piece, the 4th pipe outlet is blocked off.

Which one is right?

[bigherb]

The 'poor brother' 1.9DF gets a little less attention than other models (bit less on the Wiki, Brickwerks don't seem to stock the distributor vacuum advance unit etc) so is someone able to clarify how the 'retard' function (assuming that is what it is) is supposed to operate and what to check for? Is our vacuum hose set up correctly and any other helpful observations?:

.

The retard function works when the throttle is closed at idle or on the overun. As the fuel mixture is then very weak the timing is retarded to help burn off any unburnt fuel that would have normally been left in the combustion chamber. As soon as the throttle is opened the timing reverts to a normal ignition advance. You can run with the retard disconnected and hose plugged, the idling speed will need to be reset and timing checked to 7.5 deg BTDC at 850 rpm, with the advance vac hose disconnected whilst checking the timing.
Carb issues are more likely to cause flat spots though, the accelerator pump, worn spindles or just partially blocked jets.

Bubble Meister, yours is wrong for a stock DF

[DevonAid]

Useful comments and diagram, thanks everyone. Should assist further investigations.

[DevonAid]

Bubble Meister, does your van run ok with your vacuum hose set up? Might be a working solution for us in the short term (as accelerator pump etc all checks out) with bugherb's timing tip.
End Of The Road festival next week, be nice to be working a bit better for the journey.
Thanks in advance.