Ever since owning my MK1 1992 MX5 1.6 (car now at 105K miles) I have noticed that it is a bit hesistant when the engine is cold.
I have now replaced the oil, oil filter, air filter, spark plugs and the ignition leads (Magnecore ones off MX5parts) and it is exactly the same, no difference what so ever!
I also noticed, when removing the spark plugs this morning, that they are black on the base, but not black on the metal bit which hooks over the top of the spark point.
Is this soot build up from over fueling? Could this be linked to why it is hesistant? I also looked at the exhaust exit earlier and it is very sooty at the bottom.
I have exactly the same problem i removed the plugs a couple of weeks ago after experiencing a few stutters when accelerating and they were heavily coked. The plugs themselves have only done about 3000 miles so i cleaned them and put them back, checked them again today and they are heavily coked again. The car does not appear to smoke and sailed through its emissions test a couple of months ago so would suggest its not running overly rich. Does anyone have any suggestions?
As you say it only happens when the engine is cold, and the plugs, leads etc are in good shape I would look at the choke and check the mixture when she is cold. The black soot is almost deffinately from over fueling, but again probably only when the choke is on. Not having owned a MK1 I am guessing that they have an automatic choke.
Thanks, what you are saying makes sense and does sound like the probable cause. My car does seem to idle excessively high when the choke kicks in probably about 1500-1700 rpm and has been left ticking over a lot in the cold weather to defrost. Does anyone know if the choke idling speed can be adjusted?
On these cars it’s important to set the base idle correctly. The tickover will be somewhere in the region of your figures, but as Goof says you really shouldn’t leave any petrol engined car ticking over for long periods from cold. The over fuelling will scour oil from the cylinder bores and cause premature wear. The ecu controls the tickover fueling and supplies the correct amount for the car to be driven propery. It should be warm within about 2-3 miles [enough to blow hot air through the heater, but not hot enough to use all the revs. This takes longer. The oil has to be up to temp and that can take a good bit longer than the water]