Carburettor tuning

[davidwheeler]

There is a huge hole in the performance of my 1600 Sport in that there is nothing below 2000rpm - I open the throttle and nothing happens!   Over 2000 rpm she goes very well indeed right up to 6000+  (99octane petrol).  I know the ignition timing is correct (see my post thereon) and have adjusted the slow running screws for maximum tick-over but to no avail.  It feels as if the slow mixture is weak or if the acceleration pumps (?) are not working.  I have no information on tuning Solex carbs.  Can anyone put me on the right path before I take it down to my local wizard?
David

[lancialulu]

First check the valve timing by the protractor method rather than the notches on the cams. I had a bad flat spot where you have and could not get rid of it. I then decided to change the cams for some VAR1016 look alikes (Holbay) and timed the engine for the first time on my ownership. I now have no flat spot, a very tractable and powerful 1600 engine than before.

Tuning Solexs - my method, air cleaner off 1/4inch rubber tube to listen to hiss from front and back bank (you will unlikely get exactly same hiss due to butterfly tolerances) to balance the two sets of carbs. I use an extra spring to ensure the butterflies are closed fully to their stops. The balance screw is roughly set by winding in and out to see the engine go lumpy either way - a lowish tick over helps. one way will get the engine revving to high and the other side of the mid point will effectively run on 2 cylinders. Then you listen to the hiss and fine tune. I then go to the mixture screws starting at the front and slowly screw in (careful not to bottom roughly) and see the engine speed drop (only 20-50 rpm usually) then open up a bit to see the engine pick up - there is a delay so be patient. Do this with all mix screws then repeat the whole process probably lowering the tick over as you do each cycle.

Hope this helps.

I have just returned from 2500 mile trip doing numerous passes in Switzerland and the Dolomites when at 2200m altitude my 1600 ticked over at around 200 rpm (!) (due to lack of oxygen) but steady with it and would rev from there with no problems.

[Neil]

Not an air leak in the mounting plate (rubber) between the manifold and carbs?  Might be worth a check...

[Scott]

Hi David
The 'accelerator pumps' are just rubber diaphrams that hold a small amount of fuel to provide immediate needs on acceleration until the pump can catch up with demand on rapid throttle applications. I had an issue on my car where the diaphram on one of the carbs had deteriorated leading to hesitant acceleration issues. If your issue however is only below 2000rpm and there is no hesitation even on sudden throttle applications above this engine speed then it is unlikely to be the cause of the issue. There are some good pics on this previous forum topic if you're interested though!: http://www.lancia.myzen.co.uk/forum/index.php?topic=2199.0

It's worth asking if you've always had this issue ... or it's something that's only happened recently. If the latter it could be a partially blocked jet or, as Neil has suggested, an air leak somewhere (lack of support on the air box can cause premature deterioration of the rubber mounts as unncessary strain is put on them).

Along with previous posts on this site there's some good general advice at http://www.viva-lancia.com/fulvia/qanda/carbs/

Good luck hunting the problem down! 

[andyc]

Hi David

Just a thought and i'm not totally familiar with Fulvia distributors but is the mechanical advance working not siezed? Most distributors have some form of advance.

Andy

[lancialulu]

Hi David

Just a thought and i'm not totally familiar with Fulvia distributors but is the mechanical advance working not siezed? Most distributors have some form of advance.

Andy

easy to check dynamically with a strobe if you mark the crank pulley rather than peering onto the flywheel opening....

[simonandjuliet]

I had most problems with Fulvia carbs when they were not balanced. To that end I made a mercury manometer which really helped. Loop of clear plastic pipe, filled with mercury and connected to the 2 small bolts on top of the inlet manifold (more details and photo if required)

The other thing to check is the rubber mounting plate - a crack here and you can spend hours to no avail - whilst on the subject, check the support bar under the airbox is in place and connected or the mounting plate will crack !

[fay66]

On the other hand this twin Carburettor balancer is available for hire from myself, part of the LMC's Special Tools that I now hold.

Brian
8227

[andyc]

http://www.carbtune.com/

I bought a two column+tool case one of these which has steel rods intead of mercury, as already said by taking the 2 bolts out of the manifold balenced the carbs it works really well.

[davidwheeler]

Thank you gentlemen, I have spent the past few days working on the car.  Back to first principals.  First, I read the Workshop Manual on valve timing several times and reset the camshafts which ended up quite a few degrees different from what they were before.   I reset the ignition timing and took it out round the block but no different.  Next day I came back and checked opening and closing and found them asymmetric to the figures in the book, i.e.wrong.  I reread the book another three times and still do not understand it so I have gone back to the engraved timing marks which cannot be far out!    Incidentally, the peg for the vernier in the timing wheel is exactly similar to that of the Aprilia - and the Lambda!  Carbs were balanced by sound - I remember doing this with the Alvis TA21, an easy task as the hiss on an SU is loud.  That on the Fulvia is very quiet but I think I am about there with the aid of my stethoscope.   I have actually got a set of four vacuum gauges for the bike but not the necessary nipples to fit to the Fulvia carbs.  This only really matters for tick-over anyway.  The carbs are well supported and I am sure the rubbers do not leak - this produces a loud shriek from the induction anyway. 

That leaves the spark timing.   Fixed timing is 8 or 10 degrees advanced depending on the engine type.  Even at a tick over of some 500rpm, the timing flickers back and forth several degrees due to the play in the skew gears though there is less movement at higher revs.    I am reminded of the feeling when the Lambda is advanced to take advantage of high octane petrol but loses that wonderful low rev flexibility so I have arbitrarily retarded the ignition a couple of degrees and I think it feels a bit better.  I shall continue with trial and error and see what happens.

I have searched for a dyno curve for the 540.818 engine without success but here is one for the 1.3 engine from which one sees that there is very little there below 2000rpm anyway.  At least it is not so bad as my old Toyota MR2 2000 GT which had a power band from 5000 to 7500 rpm and was geared to do 70 mph in second gear (I've sold it!)

[ncundy]

Here's the power curve for the 540 engine.

Are you sure its the gear mesh? It would be worth checking the thrust washer on the distributor for vertical play.

[lancialulu]

Maybe I had a lucky break with my cam timing!!! The notches are only to roughly set the cams so the valves don't foul - not anywhere near an accurate setting point.

Tim

[davidwheeler]

I'm not  so sure about that, they seem to line up pretty well to me - after all, why else provide such fine lines and a check on the opening times as described in the book seemed to be pretty close.   Lambdas and Aprilias are so much easier.   Anyway, I still cannot make head nor tail of the instructions!   
Thanks for the power curves but why do they only start at 2,500 rpm?   It still feels pretty 'orrible especially after taking out the Aprilia today - such a nice car to drive pity the lights are so feeble.

[Richard Fridd]

Regarding those notches I once went through the process of (vernier) cam  timing using feeler gauges.the end result was the notches lining up exactly with the casting marks.

[the.cern]

David, a little off topic, ok, totally  off topic, about your Aprilia lights ..... Morris Parry has written about this topic in the latest Augusta Newsletter based on his experience working with a brilliant hands-on electrical engineer and general mechanical whizz afew decades ago. Funny how that description fits Morris now isn't it !!!!!

The probable cause of the dim headlights is voltage drop between the lampholder and the battery  due to poor electrical connection between the lamp and the wing, the wing and the body and possibly even the body and the battery earth. Morris's solution, run a heavy wire from the lampholder earth connection back to the battery /body earth connection.

Please try this and do let me know how you get on, I will do this on the Gussie anyway as the re-wiring is not yet complete and it will be easy to incorporate the non-standard earth returns at this stage.

                                       Andy