Technical Uno smoke

[UnoMia]

Hi,
I replaced the head on my 1100 Uno a couple of months ago with a recon unit that included valves & cam. She's running very well but I notice when pulling away from traffic lights after idling for a bit that smoke is noticable from the exhaust. When driving normally there appears to be no smoke that I can see in the rear view mirror. I've checked the timing, fitted new plugs and adjusted the carb mixture. I see that the exhaust tailpipe is quite black. The engine doesn't use much oil, (engine's done 195000 km), and the water level remains the same. Could this be carb float level or a distributor problem maybe?
Thanks in advance for any help.
PS: When I had the head off there were no ridges at the top of the cylinder bores

 

[alexGS]

Quite possibly a problem with fitting of the valve stem seals if the smoke is blue... if the seals are fitted without an appropriate drift, they can go on at an angle and the hole becomes oval - doesn't seal. Oil seeps down during idling or overrun (high manifold vacuum helps do this) and then burns off in acceleration. The oil used by this is minimal so you won't notice a consumption increase.

If the smoke is black then it really has to be a fuelling problem, such as an over-active accelerator pump (weird, I know) or maybe wrong jets in the carburettor. On a nice, long drive the tailpipe shouldn't be black. Have you tried a new air filter?

-Alex

 

[UnoMia]

Hi Alex,
Thanks for your reply. I bought the recon head from a well known franchise here that specalises in reconned heads for many different vehicles. I hope they got the valve stem seals in correctly, I don't like the idea of removing the head yet again! I do have a feeling that it could be the carb though; just as you sugested. I overhauled the carb about three years ago and I'm wondering if the float level has gone out of spec or something. I'm tempted to replace the carb with a new one as the car has done quite a high mileage and maybe it's time for a remplacement or at least another overhaul of it! I've always found the mixture screw seems to screw out more than the average vehicle's carb, which I've found to be three to four turns. Mine seems to be out quite a number of turns, although I've not actually counted them. I think that I'll pull it off the manifold this weekend and fit a new kit and take it from there. Will post any news of improvement here! Thanks again.
Andy

 

[alexGS]

I'll be interested to hear how you go

It seems a fairly rare problem (over-rich carburetion/black smoke) - usually the carburettor goes lean with age due to air leaks around the throttle spindle, and then the mixture screw has no effect (it should richen the fuel-air mix when screwed in).

Perhaps if you can see petrol 'leaking' from around the carburettor, it could just be carburettor flooding due to the needle valve not closing (perhaps it has worn out). I think in this condition, petrol washes across the bridge inside the carburettor and bypasses the jets. So I think your idea is best - to give it a quick rebuild first. Then, I think a swap might be worthwhile if that doesn't help.

Thinking a little further, I wonder if someone at any stage has drilled out the idle jet a bit too far - from what you are describing, you have the mixture screw a long way out (the leaning-off direction) and I think that suggests an over-large idle jet. Or perhaps the jet is loose!

The idle jet is not only used for idling, it also has an effect on progression (from small throttle opening to larger throttle opening), so that might explain the smoke you see on acceleration.

I've found that drilling out the idle jet from 0.45 to 0.55mm works well and I've often advocated that for people who are having difficulty getting a smooth idle (without misfiring - popping noise in the exhaust) even with the mixture screw all the way in. This is the first time I've heard of the opposite problem

If it is 1108cc I'm pretty sure that's a single-barrel carburettor in ZA, but I know the 1372cc (Pacer) has a twin-barrel carb and then there is the risk of mixing up (accidentally swapping) the two idle jets. The one for the secondary barrel is supposed to be much larger than for the primary barrel (the primary being the one with the choke flap).

-Alex

 

[UnoMia]

Okay, so I took the carb apart last weekend and installed a new needle & seat, checked the float level, etc. End result? My Uno still has that puff of smoke when pulling away from idle. I'm feeling more certain now that my newly overhauled head either didn't have new valve stem seals fitted or they were fitted incorrectly.
The next question is this: can the valve stem seals be replaced with the head in situ? I really don't want to pull the head off again! I've got several sets of seals in my workshop that have been left over from top end gasket sets over the years, so I don't even need to buy the new seals, just would like to know if I can do the job with the head in place. Motor is the 1100cc FIRE unit btw.
Thanks in advance for any advice.
Andy

 

[johorridoh]

You can replace the valve stem seals without taking the cylinder-head off.

1. by putting a short hose through the
spark plug hole and turning the cylinder up a bit.

2. by modifying a spark plug with an adaptor to a pressurised air hose.
The pressurised air will keep the valve up.

Hope you get me
Jo

 

[UnoMia]

Hi,
Thanks for the info. Just one more question though. If the valve seals are replaced with the head on as discribed what sort of valve spring tool is used to remove the valve spring colletts? Obviously the standard type of tool won't work as the head is in place.
Thanks for the help.
Andy

 

[johorridoh]

You can use a spanner socket and a plastic hammer and slam it
on the upper plate of the valve spring.
Cover the spring with a firm towel to prevent the keepers
from flying off to far.
But you´ll need a spring compressor to put the spring back in.
You might have to ask a garage to lent you one over the weekend.

edit: I found a video which might help you:

 

[UnoMia]

Hi,
Many thanks for the advice and posting the video, it's given me food for thought as to how I'm going to do my valve seals. When I do get to replacing them, (which will have to be soon), I'll take photo's of the hopefully successful operation and post them on the forum.
Andy.