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Zetec Blacktop running rich/rough idle
rm0rgan - 25/8/15 at 07:59 PM

with my cooling issues seemingly behind me I now have a new problem...

My cars running rough on idle (feels like it's on 3 cylinders at times) but certainly smells like it's running rich. I've checked the plugs and one of them looked dirtier/blacker than the others that were nice dry and brown. I could feel on the air filter some petrol around the trumpet on one of the carbs but it revs cleanly when given some beans. It sometimes runs on a bit when I turn the engine off too - especially if hot.

What should I check first - I've not had twin 40 webers on a car before and prior to spending (yet more) money it would be good to check a few of the more obvious things.

All thoughts gratefully received however, please explain in words that a four year old can understand :-)

[Edited on 25/8/15 by rm0rgan]

britishtrident - 25/8/15 at 08:45 PM

First simple thing is check the carb jets on the affected cylinder, unscrew them check they are clear and screwed them in properly.
Loose carb jets are not unknown on DCOEs

Also try swapping the spark plug into a different cylinder and see if the fault follows the plug.

rm0rgan - 25/8/15 at 08:54 PM

quote:
Originally posted by britishtrident
First simple thing is check the carb jets on the affected cylinder, unscrew them check they are clear and screwed them in properly.
Loose carb jets are not unknown on DCOEs

Also try swapping the spark plug into a different cylinder and see if the fault follows the plug.


Thanks very much - are these under the butterfly screw covers on the carbs? Will check in the morning.

kingster996 - 26/8/15 at 06:25 AM

quote:
Originally posted by rm0rgan
It sometimes runs on a bit when I turn the engine off too - especially if hot.

This can be caused by the rad fan wiring feeding back through the circuit while it spins down (hence noticeable when hot) - more common on cars with FI rather than carbs as I understand it. The solution is to run the fan off a relay instead of wiring it in directly.

Mikef - 26/8/15 at 08:58 AM

Whilst checking the jets and emulsion tubes , double check they are the same in both carbs ( not as daft as it sounds). Would also look at float levels. Do you have an airflow meter to test check the balance between the carbs. Probably the most important tool I had when I used Webers.

rm0rgan - 26/8/15 at 11:21 AM

quote:
Originally posted by Mikef
Whilst checking the jets and emulsion tubes , double check they are the same in both carbs ( not as daft as it sounds). Would also look at float levels. Do you have an airflow meter to test check the balance between the carbs. Probably the most important tool I had when I used Webers.


Cheers - will do that. Have taken them out and given them a blast with air to ensure no blockages but forgot to write down the sizes of jets etc.

It does seem better, but not as good as it was - still smells rich to me so might need to be leaned back a touch at idle (although this is all a dark art to me!)

rusty nuts - 26/8/15 at 05:43 PM

I would suggest checking the ignition system , compressions etc are OK before setting the carbs up , a misfire could well cause a spark plug to be black

Mikef - 27/8/15 at 07:05 AM

There are some good guides on setting up Webers, it is not as difficult as you think if you get your mind around it. Whilst balancing will not solve the mixture issues , it does make a huge difference to the tick over and smoothness of drive and is very easy to do with the flow meter. Will sort out one of the old guides I used.

Mikef - 27/8/15 at 07:13 AM

Link to a basic set up guide, there is a good bit on idle setup and balancing.

http://www.s262612653.websitehome.co.uk/DVAndrews/webers.htm

rm0rgan - 27/8/15 at 07:17 AM

quote:
Originally posted by Mikef
Link to a basic set up guide, there is a good bit on idle setup and balancing.

http://www.s262612653.websitehome.co.uk/DVAndrews/webers.htm


Terrific - will have a read and get a flow meter :-)

Mikef - 27/8/15 at 07:29 AM

Drop me a U2U if you want to run through it.

rm0rgan - 27/8/15 at 03:06 PM

quote:
Originally posted by Mikef
Drop me a U2U if you want to run through it.


Cheers Mike. That's excellent.