International Lancia Forums

For which reason I would not touch those secondary screws if they still have the factory wax seal and have never been touched. If you SLOWLY feed in throttle opening, how long does it take to smooth out? What happens if you pull on the cold-starting mixture? Does it idle on four cylinders then? When in doubt, disassemble and dump the lot in carburetor cleaner.

Are you absolutely certain that the ignition is behaving correctly? On my 1.3 I found that if I installed all the ignition leads in the little retainer ring intended for them they interfered with each other and the engine ran horribly. When I took them out of the ring and let them each find their own untidy paths to the plugs it ran fine. Lazy soul that I am (very un-Huiblike), I never changed that practice. I would not expect this to change suddenly as you have described but perhaps the insulation chafed from vibration.

Good point Randy. I now remember a car of a customer I had been struggling with for some time. It ran horribly for the first few miles. After the "Italian tune up" it started to behave. With new plugs it did a lot better. Finally after changing the plug leads which did not at all look suspect the car ran smoothly right from starting.

I will go with Randy also. I've heard the saying "90% of all carb problems are ignition related" after replacing all ignition components my S1 did'nt idle well and occasionally missed on the road. The problem, a brand new distributor cap was bad.

Hi Huib.
I will be rebuilding the carbs with a complete new seal kit over the next few days. I tried swapping floats, jets, plug leads, everything, but the problem remains on no.3 cylinder. When I look through the glass spark plug installed in no.3 cylinder, I can see the regular spark, but no fuel reaches it. regardless of how open the idle needle is. This initially came to my attention when the car(which had been running beautifully)just started running roughly at idle and up to 2000 revs. I took off each plug lead in turn, and each one removed caused the engine to stall except for no.3, which showed no change when removed. I thought it was a dodgy spark plug, and changed it. no difference. the the glass spark plug showed no fuel. I'll rebuild the carbs, and get that out of the way. hopefully it will solve my problems. Do you know if it is normal for the fulvia to have a small amount of vapour/air coming back through the breather pipe from the oil filler and back to the air filter box?

A small amount of air coming from the breather pipe is totally normal; that's why it's there. So long as we are thinking something similar with the word "small."

If you haven't done it, you might as well check the compression on the engine. Your symptoms don't sound like broken rings or a holed piston though.

What happens if, while it is idling (and properly warmed up), you pull on the cold starter device? Any improvement?

The rubber carburetor base(s) is ok, right? You can see easily enough if it's failing on the top side, but it's not being pushed up too hard by the support strut, so as to cause a crack in the bottom (and therefore not visible) side is it? I assume you'd be hearing some leakage if this was happening.

When you rebuild the carbs, do you first dump the components (esp. the carb bodies) in cleaning solvent? I recommend it. Compressed air can sometimes pack a blockage tighter rather than removing it unless you're able to run air through every passage in both directions. I'm not sure that's possible with some of the passages.

There is already a wealth of information here. These problems come in my workshop only once a while. Not enough to have a firm procedure in my mind. They do always get solved in the end.

You have a car which is around 40 years old. Some look to be in such good shape that it is easy to forget this. There may be many small things conspiring.

You have to go through everything and make sure it is all right which is a good idea anyway.

The carbs have to be under 4 degrees. This means the engine and gearbox have to be properly centered on the subframe. The engine is then under 45 degrees. If the airfilter support is of the correct dimensions and properly fastened, the carbs will be under 4 degrees. If the mounting rubbers are old it is a struggle to get everything in the right angles. If they are new and of the right quality, the gearbox and engine usually slide in in the correct position right away.

You still haven't mentioned type and age of your Fulvia. If it is an early one it may have two rubber carb mounts instead of one. Best change it to a single piece carb rubber.

The rubber of the actual tubes in the carb mount goes around a flange and functions as a sort of seal or gasket. If the rubber is old this sealing action is no longer there. You have to be extremely carefull and accurate when mounting the carbs onto the rubber and the rubber onto the manifold to avoid air leaks.
I use a little bit of Hylomar when mounting a suspect rubber.

Take the support for the airfilter box off. Check if the rubber grommet, the bush inside the grommet and the two saucer like washers are present and in good shape.

Stephan already mentioned that 90% of all carb problems are ignition related. I am not sure the percentage is exactly right but it is close. Of the remaining percentage half is caused by improper carb mounting. If it worked all right one day and is giving a problem the next day, chances are it slightly shifted position.

Some years ago when I had less experience and no new carbs on the shelf I always took the carbs to a specialist if the car came in not running or badly running. I simply did not (and do not) have the equipment a real carbs specialist has. If the car came in running well or at least reasonably well, I knew the carbs were properly jetted for the engine and in good enough condition. If they gave problems later the number of possible causes is limited to dirt some where in the carb or incorrect mounting or sticking needle valves. (The last is not the case. If it was, the car would run on two cilinders at idle and driving.)
This is of course after you have established beyond doubt that it is not ignition or compression or fuel pressure related.

Do not under estimate the ignition. A mixture ignites easily when it is within a rather narrow range of fuel / air ratio. If it is outside the range one needs a very powerfull spark to get any combustion and if just a bit further out of range nothing is going to ignite it. At idle there is hardly any mixture in the combustion chamber and the air fuel ratio is probably at the edge of the range if not outside.

Start checking compression, fuel pressure (it has an influence on float level) and make 200% sure the ignition is all right. All parts (plugs, cables, condensor, points, cap, cams, springs, shims) should be 100% in order. The points should be adjusted correctly for opening and timing.

Things to check also are the auxilary venturi's inside the barrels. These have a sort of aircraft wings and are often loose.

You may also try turn the balance screw such that the rear carb is a bit further open then the first carbs and see if you get more reaction on mixture screw 3. My final check when balancing carbs is to see if all 4 mixture screw give the same drop in rpm when closing them.

Based on everything you describe, ignition doesn't seem to be the problem. Which means there are 2 possibilities: carbs or valves, and you've ruled out some of the obvious carb problems. Are you sure you don't have a valve problem instead?

Hi everyone who has posted to this topic. I had no idea there would be so much information and support.
Huib, It's a series 3 1976 fulvia with around 80,000 miles on an original engine. Carb rubber mount is new and undamaged. Valve clearances are perfect, new ignition leads and all new ignition consumables about 2 months before this problem arose. I have very good workshop facilities, and I can deal with most problems myself. It's the carbs that are a black art. Ideally, a spare set of carbs would identify where the problem lies. A good set is too expensive to buy for a diagnostic tool. I'll rebuild the carbs tonight and replace all the gaskets. I'll do a compression check just to rule that out. There is very good vaccuum at the plug on the inlet manifold on no.3 cylinder, so there shouldn't be any problems with that piston. I'll drop the carbs back in on friday, and hopefully post here about the lovely drive i've had on saturday. Optimism is all I have left when my engineering skills are flawed.

Let's wait the till you have rebuilt your carbs

Do check that you have both butterflys on each carb closing equally. Best if you disturb these to reset by tightening the buterfly screws AFTER snapping shut the butterflys and looking through the venturies into a strong light (sun is good if shining and carefull not to get an eyeful!). I was told to lightly dress the butterfly disk edges with really fine wet and dry c800 grade to take off the burs that arise through use and upset the resetting. Since doing this on my 1600 I have been able to balance the carbs quite easily. PS take care with the butterfly screws as they are distorted to prevent unscrewing and may be difficult to re insert.

Tim