4000rpm without choke on start up

[Heronscourt]

I've just started my series 1.5 for the first time after restoration and initially it was reving at 300rpm I shut off and went through the carb set up again but this time it flew to 4000 rpm without choke. All the butterflies are closed, the slow running jet is screwed down. I'm using the mangoletsi throttle control system so linkages are all firm. To rev to 4000 I conclude that it must be drawing a lot of air from somewhere. I've checked all the manifold nuts, gaskets etc and the clips on the vacuum pipes and everything is new and tight. Is it possible that I've got the vacuum pipes wrongly connected and what error would produce that result. Any advice would be welcome before I wreck the engine.

Alan

[christopher storey]

It sounds to me as though you have got the vacuum pipes transposed in some way so that the manifold is connected to the atmospheric side of the servo ( the rear chamber) . That chamber must always be connected to the vertical port on the reaction valve at the front of the pedal master cylinder. Either that, or the reaction valve is faulty and is continuously admitting air to the vacuum side of the system. What I would do is completely disconnect the vacuum pipes from the manifold and block off the holes and they try again. If that solves the problem, then you need to reconnect the vacuum system making sure the correct pipes go to the correct areas ( see figs 1 and 2 in LXs3 of the workshop manual - note that the two figures show alternative layouts) If despite correct connection the problem recurs then I would say you have a reaction valve fault

[Heronscourt]

Thanks Christopher, I've checked the connections as you suggested and can't see any discrepancy with the SNG Barratt diagram in their online catalogue. The servo and reaction valve are brand new but could be faulty so I guess I need to block off the vacuum system and do the test run of the engine again. I'll post the result.

Alan

[christopher storey]

Alan : it also occurs to me that you should check the vac pipes carefully to eliminate the possibility of a hidden split in them

And as a further thought, I think that perforation of the servo diaphragm would also have the effect of admitting atmospheric air to the inlet manifold . Sorry that none of this is good news

[Heronscourt]

Went through all the settings again, put new seals on the slow run screw and finally got the file down to a slightly lumpy 1200 rpm. Just need to carry out final mixture zn tickover speed
Thanks everyone for the help.