Lancia Motor Club

Model Technical and Interest => Fulvia => Topic started by: ben on 26 June, 2018, 06:30:47 PM

Title: Carb settings
Post by: ben on 26 June, 2018, 06:30:47 PM
   Had my 1600 Sport running for the first time in a very long time and am experiencing some very strange behavior at idle.

   After much throttle joggling and on/off choke application I got the engine up to working temperature and idling reasonably but then, with no intervention from me, the idle speed gradually crept up to about 2000 rpm.
   Blipping the throttle brought it back down but only very slowly,as if the throttle valves were not snapping shut. And then it would start to creep back up again!
   I have the carbs (Solex )partially stripped now and have found nothing untoward. Return springs all good and action seems snappy.
   Any suggestions as to what I should be looking for would be welcome.


Title: Re: Carb settings
Post by: chriswgawne on 26 June, 2018, 06:41:55 PM
If its been standing for a long while as you say, are the rubber mounts cracked possibly thus leaking air into the inlet manifold?

Title: Re: Carb settings
Post by: lancialulu on 26 June, 2018, 08:44:52 PM
If not the rubber mounts I have had problems with the thin paper gaskets in the past. Solved by a thin smear of rtv silicon. I also put an rxtra light coil spring between the throttle spindle and the chassis.

Title: Re: Carb settings
Post by: davidwheeler on 27 June, 2018, 06:21:52 PM
I find it impossible to set the idle at anything less than 2000 rpm sometimes and 500 rpm at others with no rhyme or reason.   The carbs hacve been rebushed and gasketed and I rather suspect the electronicish ignition but tend just to put up with it.   I did get the 1300 to tick over nicely but sold that some years ago...

Title: Re: Carb settings
Post by: chriswgawne on 27 June, 2018, 06:55:24 PM
We have owned Fulvias of all types continuously since 1972  - probably around 15 in total - and the only slow running problems have been caused by blocked jets (so no slow running) or air leaks (too fast and uncontrollable slow running) mainly caused by cracked rubber carb mounts. Apart from one car, all of these have been running on standard ignition and I fail to see how electronic ignition on its own can raise slow running significantly.
I have heard of worn carbs being re-bushed carelessly and leaking air either along the butterfly shafts or more commonly past the butterflies which due to poor reaming are not sitting 'square' in the carb body.
Its not an easy job to get this reaming correct and this problem is quite common on Aurelia Weber 40DC carbs which of course are around min 60 years old now and are in very short supply for various reasons.
And of course if the air bleed adjusters are wound in viciously their seat will be damaged.
So to conclude, too fast slow running will most likely be caused by induction air leaks of one description or another.
Stating the obvious but sometimes its worth it.

Title: Re: Carb settings
Post by: ben on 28 June, 2018, 11:40:23 PM
Thanks for the various suggestions.

I have been stripping and cleaning the carbs today and  in the process come up with a theory---yet to be proven.
When I took the lids off after removing the carbs and tipping out the fuel I noticed that the bowl of one was wet with still a trace of fuel whereas the other was completely dry.
The flexi mount was in good condition.
All the jets were clear.
So I am speculating that one needle valve stuck shut and the revs went up as the mixture got gradually weaker on that side.

Some interesting points have occured along the way.
          The carbs--C42 DDHF---are bolted to the flexi mount and the mount to the inlet manifold with 13mm AF nuts on the 8x1.25 thread studs some of which are very in-accessable for an open ended spanner but there is not enough clearance for a normal socket.I have looked on the net for some 12 point ones to replace them with which fit a 10mm socket but the only ones I found were 45 for a pack of 10!!  Maybe I am just not rich enough to be playing with Lancias.
         Two of the four brass slow running volume control screws were seized beyond the capacity of their screwdriver slots.I very carefully filed flats on them to suit a 5mm spanner.  Having got them moving can anybody tell me how to set them.My default position is all the way in and then wind out by 2 turns.  The Concise Repair Shop Manual offers no guidance at all and the little instruction book has a photo showing the screws (on page 46) but tells you the adjustment must be left to skilled personel or an Authorized Workshop. I do not think their setting was my basic problem but it is obviously something I now have to address.
         The handbook (Instruction Book) gives jet sizes as 150 for main and 175 for air correction.(page 56),as does the CRS Manual.My carbs have 175's in all four what I assume must be the correction jets as seen in the centre of the photo's. Can someone tell me where the 150 main jets are? the jets either side of the central pairs are the size 50 idle jets.

Title: Re: Carb settings
Post by: lancianut666 on 29 June, 2018, 05:54:52 AM
Don't you use a manometer connected to the inlet manifold by taking out the 2 small plugs to balance the carbs? My coupe came with a homemade one and a couple of modified plugs. The workshop manual tells you to use mercury but water seemed to work OK.

Title: Re: Carb settings
Post by: lancialulu on 29 June, 2018, 10:07:59 AM
Main jets are on the underside in line with the emulsiontube/air correction tube.

If I remember you cannot do some of manifold adapter nuts to the inlet with the carbs in place but the can be done up with a narrow 13mm socket as can the carb nuts.

I use a small bore plastic tube to listen to the hiss of each venturi to find the balance point (it is iterative with tuning the mixture....) re tuning 42's I find it is about 1.5turns out as a starting point and turn in until that cylinder stops firing then carefully back it out until firing. Takes about an hour to set up properly or may more first time.

I have a spare adjuster if you want it which I can bring to the AGM.

Title: Re: Carb settings
Post by: simonandjuliet on 29 June, 2018, 04:58:13 PM
Re carb mounting nuts, I am going to try a set of 12 mm nuts instead of the 13mm nuts (across flats) to see if it makes fitting/removing easier.

Tim set up my HF carbs as above and they have been much better, but I am going to clean and re-gasket them so it will need to be done again from scratch.

There is an Austrian (?) supplier who provides the kits with float valves etc, etc at a reasonable price (about 60 euros delivered , I think), if you haven't already bought something, Ben

I have a mercury manometer (part of the dentist stock !) and will do an initial set up with that

Title: Re: Carb settings
Post by: chriswgawne on 29 June, 2018, 06:21:36 PM
I think one of the problems today is that Fulvia  Solex carbs which have done normal mileages are around 45/50 years old and with normal use the shafts and bushes will be worn and therefore the butterflies will sitl in different positions each time....hence varying idle revs.

And its all very well having carbs reamed with over size shafts but if they are not done very carefully the end result can easily be worse than before because the shafts wear eccentrically so where is the correct axis?

This is one of the main reasons why Dellorto carbs are so highly thought of as they have roller bearings on the main shafts.


Title: Re: Carb settings
Post by: ben on 29 June, 2018, 08:22:35 PM
     Thanks Tim for putting me straight regarding the location of the main jets. I really should have figured it out!! Thing was I knew the acc pumps were working so was avoiding disturbing the diaphragms---a) as I am allergic to spending money so have not bought o/haul kits--not yet anyway!, and b) was not expecting them to need any attention anyway which did prove to be the case. More a case of it being nice to know the jets match the spec.
     And great minds think alike Simon as I have just refitted the carbs by bolting them to the flexi mount first which is easy on the bench and then refitting the assembly to the manifold using the standard 13mm nuts for the top four studs (which are accessable with a good open ended spanner) but using 12mm nuts for the bottom four.  Actually I made these by filing down the 13mm ones. 12 point nuts would definitely be the answer if they can be sourced at sensible cost as it is still a tight thing even with the 12mm hex ones. Or alternately one might file a shallow groove where the socket spanner fouls the carb flange.
    Regarding Chris's point about spindle bush refurbishment, luckily mine have no significant wear. 
    I am familiar with the listening tube method for getting things ballanced and will try your suggested technique tomorrow Tim. Just wish you had not said it should only take an hour or so as it will probably take me all day and make me feel inadequate!!

    If the original problem still manifests itself and is down to a sticking needle valve I might try getting them ultrasonically cleaned.
    Will keep you posted.


Title: Re: Carb settings
Post by: ColinMarr on 29 June, 2018, 09:59:05 PM
There is another way of balancing the carbs! I never had any success with manometers, or with listening to the sizzling sounds from the trumpets. My best way was to set the throttle screw to a slow (and at first probably lumpy!) tick-over. Then while the engine is running pull off a plug lead from either the front or back pair of leads. If it makes no difference, then adjust the screw to increase the gas to whichever pair needs it until it runs evenly with an equal drop in revs whether you pull off a front or rear lead.


Title: Re: Carb settings
Post by: davidwheeler on 01 July, 2018, 08:44:10 AM
I have found that my car developed hesitation if opening the throttle wide at lower revs - in fact it would not pick up at less than 3000 rpm.  I increased the slow running jets to 55 with some improvement and then to 60 with considerable benefit.  Thee are discussions elsewhere on why this might be so ("modern petrol!!!")  but I found it worked and the jets are inexpensive.

Title: Re: Carb settings
Post by: simonandjuliet on 04 July, 2018, 06:42:44 PM
Re 12 mm nuts, couple of pictures showing the 2 I have replaced as a test.  A full hex 1/4" drive now fits straight onto the bottom nuts. A U/J makes life even easier

I found them quite difficult to source at a sensible price ( up to 4.50 each !!) but now have a stock if anyone is stuck or wants to try them out.