General Uno engine "jumpy"

[markoibook]

Hi guys,
My Uno has generally been very good to me, and only last week sailed through its MOT.
However, I have had a bit of an issue recently, and its concerning me.
About two weeks ago, I noticed the car being a bit jumpy - i.e. jumping back and forth a bit at low revs, and found this could be resolved by applying just a little bit more throttle. It would do it for a short while, then it would all be well for the rest of the journey. It did it twice to me in 200 miles worth of driving on a warm day, so the next day I just checked that the leads were all on ok, and didn't have any problems at all for the next two weeks.
Today coming down the motorway, the same thing started to happen again, albeit at about 65/70mph as opposed to 30mph before. Again I found it only happened when I eased off the throttle and the revs dropped, and that by applying the throttle, it would stop.
Obviously this worried me, and so I took it easy (60) and then the problem disappeared completely. If its of any importance, today it was a very hot day again.
I shall have a play with the leads again to see if it solves it again - but was wondering if anyone knew of any reason why it would do this?
I replaced the spark plugs, oil, oil filter, air filter, leads, dissy cap and rotor arm about 1500 miles ago.

Cheers in advance,

Marko

 

[markoibook]

Ideas, anyone?

 

[Chas Uno]

Is yours an SPI or carburetor Uno?

If it's SPI, it could be an ECU or fueling issue. Maybe the fuel pump isn't working properly, or perhaps the stepper motor on the throttle body is sticking? Or maybe the fuel filter is blocked?

Other than that, it could also be the ignition amplifier on the distributor breaking down, especially if the problem occurs when hot.

Pretty much a case of going over both the ignition and fuel systems until you find the cause.

Hope this helps!

 

[markoibook]

Is yours an SPI or carburetor Uno?

'Tis a carb - 903cc

 

[dave]

there is a pipe that goes into the vacume advance on your distributor, pull off pipe and see if you can blow towards the dizzy end, if you can that bit is broke.

have you done the usal new plugs, leads, airfilter, oil n oil filter change dizzy cap n rotor arm?

 

[alexGS]

903cc also has *points* ignition, so that would be my prime suspect (clean/replace contact points, re-gap (ideally with dwell meter, otherwise with feeler gauge blade) and re-time (points gap affects timing).

Many people like the simplicity of points ignition (perhaps because it gives them something to fettle on the weekends) - I'm not one of them.

Personally, I wonder how it can ever work at all. A mechanical switch opens and closes 200 times a second at 6000 engine RPM. (6000RPM/60 seconds = 100, but the distributor with four-lobe cam rotates only half a turn for one engine turn, hence the contact opens twice = 200 times. Whether it closes 200 times depends on whether the spring is strong enough, I guess... How long they are open for is also a luck of the draw...)

Practically, I think most people agree that the points ignition requires relatively high maintenance: the points gap changes (which also affects the timing, as well as the coil energy) - so I think you should start with ensuring that the points are correctly gapped and timed.

-Alex

 

[satdevil2k]

check spark plugs (correct burn colour and spacing) + wires, distributor mak. break, condensor and fuel.

 

[Morty Mort]

Had a similiar problem. Changed HT leads, and all worked fine ever after...

 

[markoibook]

Problem Sorted!

Hey guys, just reporting that the problem is now fixed - thanks to the AA!

Problem came back yesterday but was more persistent than before, so I stopped at work, had a play but no success.
So decided to use my AA membership and give them a call. Was told that I would have to wait 45 minutes, but 3 minutes later Kev from the AA calls to say he will be there in 2 minutes - on a Sunday evening!
So 5 minutes after the call, the AA man is there and working on the car. Explained to him the symptoms, so he decides it sounds like a fuel line or throttle problem.
So he wacks open the carb and begins playing around and realises that the injector nozzle isn't fitted properly. So he plays around with it and refits it, cleans out the carb, but problem is still there. Next he moves to the condensor, tries a new one and the problem appears fixed. However, after fitting a new one and playing, the problem comes back.
So he looks at the points, and cleans them off a bit, and realises that the points are earthing out. So a bit of insulating tape and a cable tie, and its all sorted.
Engine is now running ab fab, and has had the points, condensor and carb fully cleaned out and checked over.
Very impressed, as got me back on the road, and had 45 mins worth of diagnosing for free. He also had a quick scan around the rest of the engine bay, and reported that everything looked fine, and he was very impressed with the cars condition - and that he hadn't seen a mk1 Uno for years!

So I'm a happy bunny!

PS. Cheers to Alex - who got the problem spot on!