Hi there,

Im new to the forum, seems a very nice forum also. I have a problem with my Uno regarding fuel.


I usually do about 25 - 30 mpg normal driving.. However i was not happy bout this.. i tampred the fuel mixture and now engine is not working very well.. how is the screw supposed to be and how can you check if it is lean or rich and what are symptoms????



I have recently changed the oil and filter..even the plugs... and got the carb cleaner too.. however i filled it a little extra than normal oil (very little)
When i took out the plugs to check them, they were filled with what seems to be engine oil, engine seems to overheat more than normail and also when engine is normal temperature it revs at 800k, when getting hot near 90, it revs at 1200 - 1300 k. however this varies
About an hour ago before going to work i removed some oil and made it a bit lower as i though problem of oily plugs may come from there.. I wonder what can I check more?
- High fuel consumption
- Revs varies
- Minor overheating
Tnx,
Anthony Farrugia

Hello Anthony, welcome to the forum

You didn't say which Uno you have - since they were made from 1983 right up to the present date, there's a range of engines/carburettors/injection systems. You did say, though, that you have cleaned the carburettor - so that narrows it down a bit

25-30mpg in town driving would be average consumption for a 1301cc Uno 70 (1983-88), but a bit high for a 1372cc Uno 70 Mk2 (1989-94 or more recent in some countries), and definitely high for an Uno 45 Sting (1983-1991), 45 FIRE (1986-94), or 60 FIRE (1989-couple-of-years-ago-in-South-Africa...) Most of those should be averaging 35-40mpg around town.

Generally the mixture screw - if you are talking about the one on the base of the carburettor pointing sideways or rearwards - has little effect. The idle jet - which is what the engine runs on when idling or at light loads - doesn't let much fuel out and over time the carburettor develops air leaks at the throttle spindle. The vacuum advance capsule on the distributor usually fails and gives a big air leak. All this extra air means that the idle jet can't supply enough fuel to keep the mixture right, even when you adjust the screw. Usually, when you screw the screw in, the mixture is supposed to get richer. If it is really too rich, the engine slows down, idling becomes rough, and the exhaust makes a 'chuffing' noise. As you unscrew the screw, the idling should become faster (and the exhaust quieter) but if you unscrew too far, the idle speed tends to fall again as the engine is literally stumbling (popping sound in the exhaust - misfires).

The mixture screw is like a low-speed 'setting' that has most effect at idle speed, some effect when driving away, and little effect when cruising. So I wouldn't worry about it too much, but try adjusting it and see if you can hear the changes in exhaust note that I described. If not, then look for air leaks (pull off the pipe to the vacuum advance capsule on the distributor, clean it, and suck on it - yes really. If it lets through oily fumes/air easily, it's shot. There should be a strong resistance from the mechanism in the distributor). You also need to check the rubber pipe (sold as windscreen washer tubing) as it usually perishes/splits at the ends.

Something I discovered that works very effectively for most of the carburettor models is to remove the idle jet (the small one) and drill it out using a tiny drill bit. You have to be careful on the double-barrel carburettors to get the right one - the one for idling - the original size is 0.40 or 0.45mm. I find that drilling-out to 0.55mm allows enough extra fuel for the mixture screw to be far more effective and then be actually set so as to allow the engine to run smoothly. You end up using less fuel because the car drives away smoother. To get a 0.55mm drill, you can try a specialist tool shop, and then clamp the drill in something called a 'pin vice' (looks like a jeweller's screwdriver) that is used in the electronics business for hand-drilling circuit boards. It's not the sort of thing that you find in a 'car accessory shop'

Ignition timing is also important but this varies between engine type. Many of the older distributors can be turned to adjust the timing. Should be 5 degrees without the vacuum advance for the 999cc FIRE, and about 10 degrees without the vacuum advance for the 1116cc/1108cc, maybe less or more depending on year/spec.

Oily spark plugs - this makes me wonder if you have a 999cc or 1108cc FIRE engine. On these models, filling the oil is achingly slow and oil tends to run down and pool in the spark plug holes. I wouldn't worry about it too much.

Minor overheating could mean anything The gauge is supposed to sit at half-way (with a new thermostat) so you might think of that as overheating if you're used to other cars. If the ignition timing is too far retarded, that could explain the fuel consumption/general lumpiness as well as the tendency to run hot.

After a while you'll get the hang of keeping the Uno in fine fettle - generally they don't require much tweaking once you have them running right.

Cheers,
-Alex

woow, tnx man.. btw i forgot to say.. i have uno 45 (999c fire engine) 4 door 1989 model

well as you said im supposed to be doing 35 - 40 mpg so it is actually high for my uno

i actually seemed to noted than when the screw is screwed in, the mixture gets leaner and screw out it gets rich..

some tests i found out if i screw it in too far, engine works slowly as if dying and if i continue it dies eventually.. if i screw it out after 4 turns it has no effect between 4 - 10 turns as it still works normally

also i did not understand "If not, then look for air leaks (pull off the pipe to the vacuum advance capsule on the distributor, clean it, and suck on it - yes really. If it lets through oily fumes/air easily, it's shot." which pipe should i check exactly? can't find it and don't know which one it is

last thing, you said drill out the idle jet.. what is this exactly and how do i find it since as i told you i'm not that pro in engine..

thank you very much for your time and tnx for everything.. wonderful forum

cheers

Anthony

cotroler said:

some tests i found out if i screw it in too far, engine works slowly as if dying and if i continue it dies eventually.. if i screw it out after 4 turns it has no effect between 4 - 10 turns as it still works normally

Click to expand...

That's good that it's having some effect! No need to drill out the idle jet in this case. I'm still pretty certain that in = richer mixture = engine stops, and out = leaner mixture = engine speeds up.

The optimal setting is around the four turns when you notice that it's having no further effect. You basically want to adjust the screw until the engine speed is at a maximum and the exhaust note is smoothest. You might need to re-adjust the idle speed afterwards - ideally it should be about 850rpm which is fairly slow, only just enough to move the car smoothly if you release the clutch. Uno 45 as standard does not have a tachometer, so you'll have to get the feel of what the idle speed should be.

Also for economy, replace the air filter element, and make sure the tyres are fully inflated (and wheel alignment/tracking correct), rear brakes not binding (handbrake not over-adjusted). I already mentioned the ignition timing, which should be checked. Make sure the choke is fully-off. There is one remaining possible problem - if the carburettor float valve sticks or has dirt under it, the carburettor can flood. You'll usually know about this though from the smell of petrol and petrol leaking from around the carburettor, plus the engine will be difficult to restart.

also i did not understand "If not, then look for air leaks (pull off the pipe to the vacuum advance capsule on the distributor, clean it, and suck on it - yes really. If it lets through oily fumes/air easily, it's shot." which pipe should i check exactly? can't find it and don't know which one it is

Click to expand...

Sorry - should have been more clear - the pipe from the round vacuum advance capsule (on the distributor) runs to the carburettor around the back. Pull it off the carburettor, clean the end, suck it and see... should be no air movement through the advance capsule and there should be mechanical resistance felt.

thank you very much for your time and tnx for everything.. wonderful forum

Click to expand...

No probs - now, as other people are often pointing out, there is a 'thumbs up' button in the bottom right of the post - if you click it, my 'Thanks' rating goes up. I was quite happy before this was introduced (fairly recently) but now, of course, my tiny number of Thanks is embarrassing

Cheers!
-Alex

checked the pipes all ok, i adjusted the screw until i heared the engine idle smoothly, now fuel consumption is much better (i just made about 37mpg as i calculated), engine works faster and smoother, and it even does'nt require choke for startup!!!! apart the heating problem is solved too, seems that a tiny mixture screw can make so much effect!!!

that problem solved

however i have 2 minor problems, which are not too much trouble but if any 1 could help me out, very much appreciated

1. dodgy idle, when engine cold it revs ~600rpm, when getting hot it revs 800 - 1000 rpm.. is this normal or do i need to lower the idle a tiny bit? (however i cant make it too low because if i switch on the light, they would appear dimmed, if you understand what i mean)

2. i have a slight brake problem, the brake pedal seems to have hardened and brakes seem slightly less effective (i have to press with more pressure)
- checked brake pads are good, drum brakes ok too, brake fliud is to level too, what could be the problem??

also is there any way i can install an econometer to my car?? and how does it work?

tnx,

Anthony

Just a guess from similar problems.

1. Check your battery. I think it needs to be filled (distilled water), charged or replaced.
2. Check the hose going to the breaking servo unit (or the unit itself).

Alex thanks for the above info on carbs
Just a question.
My Idle jet is loose in the hole so I can ajdust it and the car works fine for a bit then it vibrates tight again.
Any suggestions? (I have tried replacing it to no avail)

Seanlr said:

Alex thanks for the above info on carbs
Just a question.
My Idle jet is loose in the hole so I can ajdust it and the car works fine for a bit then it vibrates tight again.
Any suggestions? (I have tried replacing it to no avail)

Click to expand...

Hmmm... odd problem. I think it should have a little O-ring on it. If yours doesn't, fit one. If it does, coat it with some non-setting sealant of some kind, to make it 'sticky'.

-Alex

I made 2 very slight dents in the thread and that seems to be keeping it where it belongs.

After doing the above trick with the drill my car is (so far, around 26km's worth of driving later) still running very smoothly and much better idling. Also seems to be running cooler

I had a spare carburettor in the garage so used the jet from that (it already has parts missing. I keep it for spares).

Not sure where an O-ring would fit on the jet?

Seanlr said:

I made 2 very slight dents in the thread and that seems to be keeping it where it belongs.

After doing the above trick with the drill my car is (so far, around 26km's worth of driving later) still running very smoothly and much better idling. Also seems to be running cooler

I had a spare carburettor in the garage so used the jet from that (it already has parts missing. I keep it for spares).

Not sure where an O-ring would fit on the jet?

Click to expand...

Hi, nice close-up pic there.
The O-ring fits under the screw-head, on the flat part.

-Alex

Thanks, I'll go see what the local shop has.

The Carburettor Kits I have bought so far never come with something like that.

Thanks on compliment about the pic . Cellphone camera (S-E K810I)

That's good that it's having some effect! No need to drill out the idle jet in this case. I'm still pretty certain that in = richer mixture = engine stops, and out = leaner mixture = engine speeds up.

Click to expand...

i was checking on the haynes manual and it said the folliwing:

"Where the mixture must be adjusted, prise
out the tamperproof plug and turn the mixture
screw in to weaken or out to enrich the
mixture until the engine runs smoothly without
any tendency to “hunt”."

the haynes is saying the opposite what u are saying.. which is the right one??