Technical 70 sl dying please help!

[little red rocket]

Hi guys, I'm new to the forum but I figured this would be the best place to ask. Recently I bought an 87 uno as a cheap run around ($650 NZD!)
When I bought it it was running pretty good but for the last couple of weeks its been plagued with an intermittent problem.
I'll be driving along and all of a sudden the revs drop to about 700 and loses all power. Sometimes it comes back to life after a couple of seconds and does a bit of a backfire if the accelerator is well depressed, but most of the time it just slows down and dies once under about 20km/h. Mostly it'll start after a couple of attempts but sometimes it takes a couple of minutes of ignition off to make the magic happen. Or it starts with much coughing and spluttering. This can be a bit of a hassle when driving round town :doh:
Im not much of a mechanic myself but it NEVER happens when I have somebody knowledgable in the car. :bang:
There doesn't seem to be any rhyme nor reason why it happens- doesn't matter whether its hot cold, going slow or fast, just heading down the drive or 20 minutes into a trip. Battery leads have been tightened and battery itself is ok. I've been told there are sometimes rubbers in the inlet manifold that perish and cause problems
Thanks for your help, Tim

 

[alexGS]

Yet another Kiwi :woot:

I think you have blocked carburettor jets - which will often un-block and re-block themselves as the fuel swirls around. Take the top off the carburettor (8mm nuts hold the air filter housing on (and one 13mm nut on the top of the camshaft housing), then there's a number of slot-head screws that hold the carburettor top on)

Remove all four of the jets (they look like brass screws) - note carefully which one goes where (perhaps scratch tiny marks on the top 'screw-head' surface) - take care not to damage the hole in the top of the two larger jets, as that hole is a calibrated air corrector (air intake).

Sorry for the total lack of pictures - I can't seem to lay my hands on any at the moment

The carburettor has two halves (known as chokes, or barrels). The primary half has the choke flap fitted (note the term 'choke' means two different things; either the carburettor barrel, or the mixture enrichment device...) If you look down through the carburettor, you'll see that the primary throttle opens before the secondary as you operate the accelerator cable. Inspection of the jet outlets in the carburettor will show you which jets relate to which half - quite simply, as you look at the carburettor, the two jets on the left are for the front (secondary) half, the two jets on the right are for the back (primary) half.

The two smaller jets are known as idle jets (the primary idle jet is for the engine idling, the secondary idle jet is for progression between half-throttle and full-throttle operation).

The two larger jets are known as main jets. Each is actually an assembly of three parts that are a tight press-fit - the top 'screw head' is the air corrector, the middle brass tube with all the holes is the emulsion tube (responsible for some fuel/air mixing), and the bottom part is the main jet itself.

Jets have the size engraved in tiny numbers around the bottom. A Haynes manual lists the sizes - typically an Uno 70 will have a 0.45 primary idle, a 0.90 primary main jet, F42 emulsion tube, and a 2.20 air corrector. On the secondary side, the idle/progression jet is 0.70, the main jet 0.97, the emulsion tube F38, and the air corrector 1.75.

Jetting does vary (I have seen a 1.40 main jet) and some people (myself included) like to drill out the primary idle jet to 0.55mm to allow better mixture adjustment for smoother idling. But the main thing to be sure of is that the jets are not accidentally swapped around - it does happen...

With the top off the carburettor, mop out the petrol with a rag, then use compressed air to blow all remaining fuel and debris out. Often, the problem is caused by gasket sealer residue on the cardboard carburettor gasket - so wipe that clean carefully (when you reassemble, don't use gasket sealer - it's unnecessary). The fuel inlet has a gauze filter under a large brass nut. That should catch the worst of the debris in the fuel but obviously it won't catch debris that falls in from the air filter or the carburettor gasket.

You can also fit an in-line fuel filter, which can be a good idea, but I have a personal thing against plastic fuel filters (think what happens if it splits) and in my experience, the gauze filter on the carburettor is fine enough to catch the rubbish that could block jets. As I said, most of the problem is not carried in the fuel but instead falls in the carburettor from the intake or the carburettor gasket.

Also clean out the inside of the air filter housing and maybe treat it to a new air filter while you're there. Be careful not to overtighten the carburettor screws and air filter nuts - the threads are quite weak. You may find a couple of the air filter nuts are missing or that the threaded studs come out. That is fairly common - just try to refit everything as best you can.

With an old car that is new to you, it's often best to work by a process of elimination; so even if cleaning the carburettor doesn't solve the problem, at least you then know that's OK - fair enough?

The inlet manifold perishing you mentioned - I can think of two possible things that could mean - the FIAT Tipo (similar engine) has a rubber carburettor mounting that perishes and splits, and causes all sorts of running problems - but your Uno doesn't have this. Both engines have water (coolant) running through the inlet manifold and if the inlet manifold gasket is faulty, water can leak into a cylinder, causing the engine to start on three cylinders. I don't think that is the cause of the running problem you mentioned, however.

Best of luck and welcome to the forum! :wave:

-Alex

 

[little red rocket]

wow thanks for that alex! I may endeavour to clean it out tomorrow. will post an update when I have done.
today I drove a few hours and it ran faultlessly which seems consistent with what you are saying too.

 

[alexGS]

Super-fast reply there from you

These cars are prone to an ignition problem as well - the famous finned box on the side of the distributor - that can die completely (as though you'd switched the ignition off) and 'recover' when the engine is off for a while, but from the symptoms you describe (including the 'spluttering' and 'backfire' etc.) I think you have a fuel problem this time.

I know when you read posts like this you probably wonder what you're getting into But really, these cars can be pretty trouble-free once you've gone over them thoroughly - as they're at least 20 years old, they tend to need that TLC to get them back into fine running order. So best of luck with the carburettor and then we'll move on to something else 'if symptoms persist'

-Alex

 

[little red rocket]

urghhh

wish i never took it apart. But I did. There was no crap in the carb filter or the jets. put it back together and it didnt go at all. got it down to the local mechanic who got it going again mentioned something about it not getting enough air and the air intake having a valve that wasn't opening. it ran good for the day but when i took it out that night halfway through the trip sitting at an intersection it stopped and wouldn't start for ages. carried on and got within a couple kays of home and it bogged down and wouldnt start at all. tow started it today. it will only start with a tow and this takes a bit of doing. after the first time it went ok, went for a drive for a few minutes but cut out coming into a driveway. tow started again and now it runs like a complete bag of **** and dies at random times. won't run under 2000rpm. no cooured smoke coming out of the exhaust but sounds a bit like a rally car! have tried everything for starting it - ether in the intake, air filter housing off. just ain't going. seems destined for scrap metal at this rate.

p.s alex im not blaming you its just my poor mechanical skills lol and im a bit frustrated. any ideas?!?!?

 

[alexGS]

Re: urghhh

Sorry to hear that things are still not right

Is it possible that the fuel pump doesn't work well enough to fill the carburettor? That might explain why you need the tow start or why it won't run below a certain speed. It would tally with the cutting-out after sitting stationary for a while. The fuel pump is mechanical, mounted on the front of the engine block, and has a pushrod that sometimes wears down. That reduces pump output to the point where, when the engine is idling, it may not be pumping enough. When you took the top off the carburettor, did you find about 2cm depth of petrol in there? With the fuel pipe disconnected from the carburettor and the engine cranking over, does a 'normal' amount of petrol come through? Difficult to describe 'normal' but should be about a tablespoon of petrol in a few seconds of cranking. It's not an amazing squirt like electronic fuel injection would need, but it should be more than just a dribble.

To check the fuel pump pushrod, undo the two 13mm nuts that hold the pump in place, then take out the spacer block and inspect the pushrod - should be smooth on both ends. If one end has a 'munched' look, that could be the problem.

That mechanic was clutching at straws, trying to blame the hot/cold intake valve on the air filter when really, that has no effect on anything. Unless he meant the choke flap in the carburettor - which has to be open when the choke is off.

You'll appreciate that without being able to watch and hear the engine running, it's difficult to make any proper diagnosis. I'm beginning to wonder whether it is a fuel or ignition problem now. I'd want to check the ignition timing to see if it is correct - when you say it's running like a bag of bolts, that to me means either the timing is way off or the carburettor has a blocked idle jet so it is having to run on the main jet (badly/too lean).

When it won't start, have you checked for spark at a removed spark plug? That's still always a possibility as I mentioned before; the finned alloy box and the pickup wiring are known problems. There is also a chance you have contact-breaker points ignition in an '87.

These are simple cars BUT they are now old and it's possible for lots of things to be wrong. More than two things wrong at once and the diagnosis becomes really difficult. Once you've had the chance to go through things and sort them out, the car can be reliable again. I hoped that cleaning the carburettor would eliminate one 'unknown'...

I think it might be time to find a FIAT specialist locally as sooner or later, you'll probably need some replacement parts as well as advice... sorry about that... (wish you were in Hamilton! )

-Alex

 

[jjhepburn]

Maybe its the fuel cutoff valve on the back of the carb? Not sure how you would check it as I dont know if it opens with 12v or if it closes? But that could be a cause of the engine cutting out.

 

[Chas Uno]

Maybe its the fuel cutoff valve on the back of the carb? Not sure how you would check it as I dont know if it opens with 12v or if it closes? But that could be a cause of the engine cutting out.

It's open with the ignition on, but only affects the idle circuit. It wouldn't stop the engine from running at partial to full throttle openings.

I'm suspecting it's more an intermittant ignition problem. A dodgy wire, lose contact, failing module or something of that ilk. Double check all the ignition system components especially on the low tension side. Be methodical and I'm sure you'll find the fault sooner or later

 

[little red rocket]

Yeah it seemed to be putting in enough fuel. I checked that there was spark as well. But I have some good news (sort of). The mechanic had another look at it - I had to tow it down but he managed to drive it into his garage:bang:

Anyway he said he was checking the plugs and he had spark and then all of a sudden it disappeared. Later on it started fine without any intervention. So he thinks its most likely the distributor. I haven't had a look myself - does the finned box house the rotor? I have a mate with an uno 45 of the same era in his rubbish dump on farm. Would the distributor be the same? It's a 45 min drive each way and I have to borrow a car to get there so it'd be good to know if it will be a waste of time making the trip. Thanks :yum:
​

 

[alexGS]

The finned box is the amplifier module that drives the coil - so yes, a very likely failure. Failure can be quite intermittent too and give rough-running. Also likely to fail is the pickup wiring inside the distributor - it loses its insulation.

The module is interchangeable with the one on an Uno 45 999cc FIRE, but NOT with an Uno 45 903cc Sting. In NZ, the Sting was sold in the same years as the FIRE, so you have to be sure of which it is before you drive out there.

Alternatively perhaps there is a FIAT dismantler in Christchurch that has a spare sitting around?

Ironically I shall be in Christchurch tomorrow (Thursday) - will send a private message just in case we can meet up in the afternoon/evening

Thanks,
-Alex