Fuel blockage?

[nistri]

Assuming that the breather pipe is clear and that the filter(s) are not blocked, it would be useful to disconnect the fuel supply hose to the rear carb and (using the electric pump) to see if there is a steady, good flow of petrol into a glass jar or even better a calibrated measuring cylinder. As an aside, it is interesting that some electric pumps deliver less fuel pressure than the standard mechanical pumps.

I would take Jai's comments about the electronic ignition very seriously as several of these units are known to give problems after a long service, especially when the engine is hot. Could you try to see if the problem persists by temporarily refitting the the standard ignition system? Finally, check that the servo hose running from the intake manifold is in good conditions: try to twist it while the engine is running and see if the revs change. Good luck.
Andrea

[Scott]

Woah - coincidence Andrea. I'd just been mentioning you in an earlier posting in this topic. A belated thanks for the Viva Lancia article on the 'priming' pump by the way! 

Many thanks for the additional tips. I'll try these out too.

[Scott]

 

Many thanks for everyone's assistance on this forum topic.

My car is back to running as it should so all the advice you guys have given has worked really well ... thank you once again.

[ncundy]

So what was the problem - don't keep us hanging 

[davidwheeler]

Take the tops off the carbs and remove the floats and the jets.  You will be amazed at the amount of mud you will find in the bottom.

[Scott]

Sorry 'ncundy' - wasn't trying to be mysterious!

Using the (separate) 'carb prime' electric fuel pump I have installed I emptied the fuel tank into a jerry can - ensuring I had an 'inline' filter in place while pumping out the fuel to ensure that any sediment was caught.
With tank empty I unscrewed the drain plug. Thank you Lancia designers for using a brass plug - this unscrewed very easily. The small amount of fuel remaining was drained into a receptacle - some sediment was definitely present (but thankfully not as much as I had perhaps expected based on the advice from 'St Volumex'). I was also surprised at the good condition of the filter assembly in general based on earlier comments from contributors: the 'arms' that hold the filter were 100% although the filter itself had a small split. I exchanged the mesh as recommended. I can see that my earlier question on how the filter fitted was wide of the mark as I was imagining a plastic hose that had to be attached to the filter rather than a small diameter metal pipe that sits inside the filter as it is moved back into position.

Taking into account Jai's comments I also took a quick look around the electronic ignition (Lumenition Optronic system). Nothing appeared specifically out of place - wiring intact etc. I then twigged that an area of soundproofing felt on the underside of the bonnet was unstuck and drooping. We're only talking about a relatively small area - but by sheer bad luck this coincided with exactly where the 'controller' module for the ignition is situated when the bonnet was closed! If this was affecting air flow around the module this could have explained something if such a system can play up when overwarm. I've stuck this felt back with some glue and copious gaffer tape for now but I really must investigate getting some new shiny foil backed felt as the stuff under my bonnet is a bit shabby.

My money's still on the fact it was a fuel issue though since the problem was only manifesting itself at higher revs but I'm no electronic ignition specialist!

Many thanks to the other contributors for suggestions at the carbs ... I would have come onto working forward to this area next (and the tips are stored in my memory banks for later retrieval!) but now the little beauty is running okay I'm happy to leave things as they are ... although I will be doing some TLC tinkering over the summer.

All the best for now and thanks once again.