Lancia Motor Club

I am having a bit of a problem setting the tick over of my recently rebuilt 1.3 engine. The engineer at a local garage doing the voluntary MOT had the same issue, the engine gradually slows down when idling to the point when it is about to stall, but setting the tick over higher means it races at 1500rpm before gradually slowing to around 1000rpm. The carbs are Solex PHH35s, and I have 123 ignition. The carbs were rebuilt including new seals around the spindles, I don't think the spindles are sticking as I can push the linkages fully shut without any noticeable effects. Has anyone any ideas?

Could be the synchronise screw out of balance coupled with poor mix setting on each choke. Tuning is an iterative process, but must start with ignition and cam timing correct and tappet settings also.

I think I'd check the air flow going through each venturi with a flow meter. If they are out of balance, it can make the idle level a bit unpredictable.

It sounds like it`s too lean at idle. If you turn the idle speed screw in, to pick up the speed, you are moving  the throttle plate (butterfly) and thereby exposing the progression holes, which in turn will draw in more fuel and cause the idle speed to rise too much. Try turning the mixture screws out 1/2 turn at a time and see if that improves it. The other possibility is that it needs to go up a size on the idle jet to compensate for the modern Ethanol added fuel. Personally I use Esso 99 plus, it has no Ethanol in it even though the pump states E5.

many thanks for the responses, I will have a go! ;D

I have found a load of unrelated things wrong with my carbs setup- the mechanism that operates the accelerator pump on the second carb was not working, a small pin was missing. The first lever on the accelerator mechanism was hitting the body of the carburettor resilient mountings when fully off meaning I could not slow the tick over down on the adjustment screw. The main problem though seemed to just be the adjustment on the first carb butterfly that equalises the movement between the carbs, I have found a setting that seems to work in that it now ticks over steadily at about 1000rpm, if I slow it further it still tends to stall. I have been reluctant the alter the mixture controls as they were set up by the local garage but now I have made some progress I might try a bit of enrichment. Thanks again for the advice!

i would not worry about what the garage did. If they "tuned" the carbs in the state they were in the mixtures will be way off.
As suggested, get the engine really warm and set idle to 1000 rpm. Adjust air flow with flow meter so carbs are balanced. Then adjust mixture screws, Start 1/4 turn out on one and see what rpm does. If it drops go the other way and turn turn in 1/2 turn. Find the point where engine is running at highest rpm and is smoothest and that will be about correct. Then do the other and recheck balance
You will need to take the air box off to get to the carb intakes. You can adjust the air balance between the two chokes on the carb but i would not bother, just get the balance correct between the two carbs on the adjust screw between the 2 carbs. (make sure you have the correct one, one is the idle, one is the balance.
I spent hours/days getting mine correct but eventually got it right.
I agree about using Esso 99  Zero ethanol.
What are the state of of your idle mixture screws? If old/pitted/bent/blunt/ then get new ones.

If the garage replaced the rubber manifold adapter then quite a few of these pattern parts foul the throttle lever at zero. Nothing for it but to relieve the metal between the 2 carbs.

To check balance you can use the listening method with the air box off, and use 1/4" fuel hose to listen to the hiss of the carbs (same pointon each trumpet. Use your ear to average out the hiss from all 4. You want 1+2 = 3+4. The balance screw (forward one) with adjust the hiss. The tick over is lowered by the other screw. You want to aim for 900-1000.

You can use a venturi balance meter like this in place of the pipe https://www.amazon.fr/Deluxe-Carburetor-Airflow-Latest-Rage/dp/B00CMC57R0/ref=asc_df_B00CMC57R0/?tag=googshopfr-21&linkCode=df0&hvadid=353922224844&hvpos=&hvnetw=g&hvrand=16078163744475138424&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9108545&hvtargid=pla-568420224882&psc=1&tag=&ref=&adgrpid=78295457264&hvpone=&hvptwo=&hvadid=353922224844&hvpos=&hvnetw=g&hvrand=16078163744475138424&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9108545&hvtargid=pla-568420224882)

Generally I find the balance screw finds the minimum engine speed. Either side the engine races on 2 cylinders and is lumpy. I use an accurate rev counter in the engine bay to fine tune the 4 mix screws. Individually slowly screw in till the engine slows ever so slightly then screw out slowly (maybe no more than 1/4 turn). It is iterative.

Also if the carbs have been off there may be air leaks round the gaskets which will need sorting before any of the above, and of course ignition timing and tappets/valve timing require confirming/adjusting before the above.

Thanks everyone for the sound advice! I will have a go at the carbs shortly, I am deeply involved in replacing the lower wishbones right now (see other post). By shear chance a pair of unmodified wishbones have popped up on ebay which I have grabbed, I will have a go next week if the weather improves. (I am working outside now!!)
The engine was a complete strip down and rebuild including carbs so there could be any number of things wrong. Certainly the tappets need a bit of tweaking as they are a bit clattery at the moment. The valve timing I believe is correct after an epic struggle to understand how to adjust vernier cams! I replaced the chain and tensioner and all the marks ended up in line which was great.
The mixture control screws appear clean, not corroded so should be serviceable. I will try one of those flow meters and a colortune to set them up and see how we go.

I have found ears a better diagnostic than colourtune on a fulvia engine