HI, I have a mk4 cortina 1.3L with it s standard engine that has around 88000 km, it starts fine even in cold weather, and while chocked it misses a little but works, when the engine gets to temperature and i turn off the choke, it idles fine and at constant throttle it works fine too but as soon as i push the throttle pedal down the engine feels like it s gonna turn off, then it backfires 1 or 2 times and revs up....

I checked the spark plugs 2 of them where black and 2 where orangey i changed all 4 and spark is coming on the plugs. Could it be the timing is a bit off?? or the carb needs a service kit (I think that the carb never got off the engine).

P.S I have a small whole in the exhaust pipe near the gearbox and the fuel filter isn t always full could any of those effect??