Tuning Carbs

[NRG]

Hi, I wonder if anyone can help.  I have just woken my car up for 2015, and she's running very rough.  No power and especially bad when under load, accelerating etc. Sounds like a major misfire... The car was fine when she went into hibernation in November.

The engine is a Zetec 1.8 running off twin Weber DCOE carburetters.  I have never really had to touch the tuning in nearly 20 years of ownership as mileage is low.  Now moved to Corhampton, Hants, on the A32.  Anyone have any rules of thumb to tune, or a good contact to get reasonably priced professional help nearby?

Thanks in advance

NRG

[Paul Deslandes]

First question - do you have a choke and have you used it?  If so, admonish yourself and then work the choke pull back and forth a few times and see if it improves.  The so-called choke, it's actually a fuel enrichment device, is the spawn of the devil and a common cause of problems.  Otherwise, it could be a stuck float in one of the carbs. Give them a sharp tap (not too hard) which might free them if stuck open.

Have you had the plugs out and are any of them very oily or wet with petrol?

Paul

 

[andy_h]

Hi,

could be a number of things including;-

old fuel

Dirt in the carbs

broken/warn spark plug 

HT lead breaking down

Coil pack breaking down

etc

i'd go for the easy checks/changes first (new fuel, new plugs, new leads in that order).

if after that then you could take to Airey Tuning he's old skool with a rolling road in his garage.

 

[Terry Field]

Hi,

The carbs are likely to be a distraction unless you have been messing around with them,

I would start with plugs - if you haven't changed them for a couple of years, do so.

Ditto the HT leads. These can break down and cause all sorts of problems - again if you haven't changed them for a couple of years, then I would try that.

Once you have checked those, follow Paul's approach

Cheers

Terry

[NRG]

OK Guys, thanks for all the helpful comments...

 

First...no choke is fitted as far as I know...nothing driver operated anyway...although I gather there's an automatic system, though not sure where it is or how it works...

Went back to the car cold this morning....and fired her up without doing anything at all. Within 30 secods I could tell that the No 2 cylinder (second back from the front) was not firing because the exhaust stayed cold while the others heated up quickly.

Took off the spark plug lead and there's a nice electrical flow....so the plug itself was suspected immediately.  Changed that straight away and she's now running on all 4!  Normal smooth tickover and smooth pick up when revved. Though the 2 exhausts at the front of the engine are not as hot as the ones at the back after 10 mins running in the garage...

I could't see anything particularly different about No 2 spark plug compared to the others...not oily or wet or anything special.

I changed the other plugs for protocol's sake and am waiting for the storm to blow through to do a road test.

 

NRG

[martyn]

It seems to me that winter hibernation is a pretty good way to finish off spark plugs that are already on the way out.

I had a similar problem with some slight misfires creeping in before the winter break. When I got the car out in the spring it was completely undrivable and would struggle to even idle.  Swapped to a new set of plugs and it ran perfectly.  I'll make it part of my yearly routine now, even if not necessary. Only costs a few quid

[Paul Deslandes]

Glad to hear it was that simple.

One thing that can foul plugs is running them for a short time and shutting off before they've got properly hot.  NGKs seem particularly susceptible to this. On occasion I've just moved the car in and out of the garage, or off the trailer on a cold damp Sunday morning, so it hardly gets warm and it's been really difficult if not impossible to start, particularly if its been running very rich.  A good soak in carb cleaner usually does the trick although, as has been said, they're cheap enough just to chuck and replace.

Paul

[Jonathan Kay]

Better than chucking...

Jonathan

[Klunk]

Just picking up on the different exhaust header temps,  check the air flow balance between your carbs.

Regards,

Giles

[NRG]

This has all been really helpful.  Thinking about it a little, the performance was a little haphazard in the last few days of running in the autumn...which I now realise, could be the early signs of spark plug degradation, though I had no idea at the time.....

Yesterday, we went on a 70 mile run, around Winchester, Southampton, Hamble etc and the engine was a lot smoother that I can recall for ages. No spits or overrun and a nice smooth eager acceleration profile.

I have ordered a flow meter and will attempt to adjust the air flow to balance up the carbs....there's definitely a little work to do as she's a tad lumpy at tickover still.