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Old 15-05-2007   #1
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Smooth idle and warm/hot starting

Not really a major issue, as the 60s has always done this, but I'm sure "from factory" these issues weren't with it, so ideally I'd like to get it rectified and get her running pretty much perfectly.

The car is: Fiat Uno (Mk2) 60s 1108cc, with manual choke and carb.

First "problem" is when warm, and running at normal idle speed (the car has a manual choke). Inside the car it feels relatively smooth, although perhaps a bit "lumpy", however outside, you can here the exhaust kind of "coughing", and almost popping, as if it's running too rich. Ultimately not a major issue, and perhaps I'm expecting it to be smoother than it was always meant to be?

Second "problem" is warm/hot starting. On a cold day, or from cold, she needs some choke, a quick flick of the key and she fires up. You barely hear the starter motor as she's so quick at catching. But if you drive her up to normal temps, leave her for about 10 mins parked, and come back to her, she won't fire, unless you dab the accelerator while turning the engine over, then she'll fire up but for the first 15 seconds or so she feels quite rough, this clears and she drives normally afterwards. Leave her for a shorter time and she'll fire straight away. Leave her until she's cold again, and she'll fire straight away.

Do you think the two are connected. Slightly rough idleing, and poor starting when hot?

Are there any modules or parts that can easily be replaced, which might help with this.

She has new:

Plugs,
Leads,
Distrubutor Cap,
Distributor Rotor Arm,
and been serviced about 3 months ago.

I'm thinking the vacuum advance, on the top of the distributor? Or is there another module (ignition module) to look out for?

Once again any help would be great.

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Old 18-05-2007   #2
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Re: Smooth idle and warm/hot starting

Hi Circolo

The problem you describe with slightly rough running and popping from the exhaust is the exact same problem that I had with the uno I recently purchased for a friend, and my own uno when I had it.

I would certainly recomend changing the vacuum advance unit on the distributor. the unit has a rubber diaphram inside that will probably be corroded as your car is likely to be about 15 years old if it has a carb.

I changed this on my car, it is a simple task, the part is only 15. To fit you must first remove the three screws securing the unit onto the distributor. Then I carefully used a flat head screwdriver to "pop off" the plastic arm by carefully levering down the right hand side. Then carefully lever from the opposite side to pop the new unit back on and screw it on tight again with the three screws.

When changing the unit I noticed straight away the engine idles much more smoothly, as you would expect it too straight from the factory.

Unfortunetly I am not sure about the hot start problem. I take it that you are depressing the accelerator about halfway when starting from hot? this should help.

Cheers

Phil
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Old 21-05-2007   #3
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Re: Smooth idle and warm/hot starting

Hi Circolo,

Sorry for the lateness of the reply I've been very busy lately.

It might be time to check the valve clearances. Popping from the exhaust may signify a burnt valve, so if you find no clearance, it might be a head-off job in the worst case. But this is fairly unlikely - more likely to be a mixture problem. I don't think that there is an ignition fault.

Vacuum leaks are a very real possiblity, as Phil said, but also my favourite culprit is the idle jet in the carburettor. I usually drill this out from 0.45 to 0.55mm, as this allows the mixture screw to actually work properly and helps you get the engine running more smoothly. In fact the 'popping' from the exhaust could be simply misfiring from running on a weak mixture.

The hot-starting sounds fairly normal. Make sure the carburettor heat shield (Bakelite plate) is intact, since if the carburettor is hot, it may be 'burping' fuel into the engine after switching-off. That is why you need the extra throttle to allow some air in to dilute the extra fuel.

The original handbook even states to depress the accelerator slightly while starting, also as Phil said. So it's nothing new

-Alex
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Old 22-05-2007   #4
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Re: Smooth idle and warm/hot starting

Thanks for the advice chaps.

By the sounds of it, I think it's the vacuum advance on the distributor. Although the carb may have a question mark over it. (Occasionally when I switch the engine off after a long drive, I get over-run, where the car tries to carry on running briefly after the ignition is switched off). That said, that could be because I have raised the idle speed slightly to compensate for the rough idling.

As I mentioned before, it's not a major issue, but as the rest of the car is pretty much perfect, it would be nice to have a smooth low idle speed too.

The hot start issue, seems to be acceptable as it is. Looking in the Handbook, it states the gas pedal should be applied a little to start the car when warm, which is exactly what I do, and it starts. I'll check to see if there's shielding, if not, I'll find something to shield the carb from heat.

Thanks again for the help, gonna get that vacuum advance unit ordered....

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Old 22-05-2007   #5
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Re: Smooth idle and warm/hot starting

Vacuum advance now ordered, 12 from Desira Diss. Orignal part.

So far to do this weekend:

New Front Calipers,
New Rear Cylinders,
New Rear Shoes,
New Rear Drums,
New Lowered Springs (-40mm all round)
New Vacuum Advance Unit,

My challenge: To do this in less than two days.....
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Old 22-05-2007   #6
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Re: Smooth idle and warm/hot starting

Excellent - great price for the vacuum advance.

Sounds like you have your work cut out for the weekend! Good luck with those rear brake shoes, they were a pain to get right on mine!

Let us know how you get on with all the improvements/upgrades

Cheers

Phil
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Old 23-05-2007   #7
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Re: Smooth idle and warm/hot starting

Thanks for the "good luck", I reckon I'll need it....

I'm going to try to do a fall guide, with pictures for some of this stuff. Some of which will come in handy for the Uno (as well as the Punto) crowd on here.

I've played around with the rear brakes a few times, so I'm sure they won't be too much of an issue..... although I can myself with some of the work I'm going to do.

I think the main issue will be the weather which looks to change for the BH weekend in the UK, from the nice warm sunny weather we have at the moment to wet, cold and windy. :shakehead
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