Wondering if u could help me out with this one. i have a mk3 fiesta 1.6s its basically got the lean burn XR2 engine the head has been ported and flowed on the intake ports aswell as them being straigtened out. i only done a bit of constructive work to the exhaust ports since i couldn't see much a way of improving them since they where square. it's also had a 30 thou skim.

My problem is the car seems to miss or strugle a lot under load around the half throttle 1/4 to 2/4 throttle mark it does it in 2nd when the engines cold, when it's warn it's only really in 4th and 5th but u can notice it in 3rd aswell under certain posistions. it's only when accerating and it starts missing and only gets better when u let off the throttle or push it down to full throttle and then it's ok, i've put new plugs init and its just had a new altentator so the coils getting the right voltage, the HTT leads test at only 8000 ohms so they are fine. i always use optimax, also the intake manifold has had the water chanell blocked of to allow it to run cooler could this be the problem. or could it be pinking or a carb problem it be like this ever since the 30 thou skim, its still got the TLD carb on it i've adjusted the mixture to get it to idle better would this affect it since this is only supposed to be the idle mixture on this carb. also the timing is still standard on the mark.

PLEASE HELP I'VE BEEN TRYING TO SORT THIS OUT FOR SOME TIME NOW

 

HI,

Sounds like maybe the compression ratio has change by skim,
not sure how much it would alter by 30thou,
are you saying it is pinking, could do with seeing what the co% is on load
to check the fuelling, maybe weak mixture, do you have the correct grade of plug's
fitted( heatrange) when it struggles as your on a carb, try putting the choke on
slightly to see if it helps, ie richens the mixture when you get the flat spot.
sounds like weak mixture,

DAVE R

 

Cheers the carbs got a Auto-Choke so thats out of the question, the Compression Ratio would have changed but its only 30 thou so i would have thought it would be ok im still running the standard cam, witch could cause this a bit but i wouldn't of thought this much. since i know people who had had 40 thou + and still no problems with standard cam. im not sure if it's pinking don't really know what it sound's like. its got a K&N on it aswell and with the headwork it's probally running a bit lean already, the plugs are proper NGKR V electrode ones meant for the 1.6s. whats the best way to richen up the TLD, can it be done by adjusting the idle mixture screw (alan key one) Cheers. actually i don't think it is running too lean since it does it when the engines cold aswell witch would mean the Auto-Choke is on and it would be running a lot richer anyway. PLEASE HELP ANY MORE IDEAS.

 

HI,

ok twin choke 2v TLDcarb, the idle mixture wont cover the full load reqirements,
without going to all the technical of how this carb works, you have a power valve IS THE CARB GOOD,diaphragms etc,
for full throttle use, are you sure the auto choke is working correct, as you say
it is the same when cold,if you remove the air filter when the engine is cold the
choke flap should be nearly closed, check you dont have any vacuum leaks anywhere on the intake side of the engine, causing a weak mixture, take the plugs out when the engine is warm after a run and check the colour to see if the plugs
are suited for the engine, pinking sound is like a metalick clinking sound, like a metal object in a can? if you hear it under load back off the throttle,especially on a
turbo charged car as this is known as the death rattle for good reason,,
if no vacuum leaks are found, i would ask a your mot station if they could run your car to show the cruise fuelling, i know its not under load conditions but may show a fault , need someone with a rolling road, or a good mechanic will sort in a hour or 2, as it is ,go over your step of whats been done and when did this issue start,

DAVE R

 

Carbs fine i stripped it and cleaned it a while back the cars only done 60k so it isn't worn much, auto choke's working fine. plugs come out the right colour (brown to light brown) don't think thiers any vacuum leaks i checked a while back by putting a water hose on the intake and carb ect. someone from the RS owners club said it could be the coil breaking down underload is there anyway to test this theory.

before it used to just labour like they do and make a deep noise from the exhaust like they do but know it kinda like it doesn't accerate it just stays the same and make a funny noise from the exhaust like the same rythum as a machine gun intill u give it full throttle and it clears up and accerates fine.

 

HI,

never heard of water for vacuum leak check, try propane gas the type that screw
on to a gun type thing for plumbing use, could be the spark breaking down
under compression, also check the fuel pump is giving a good regular spurt of fuel,
check the coil primary and secondary ohms reading, you say checked leads
what about rotar arm and cap,
if it was on a machine such as a crypton tune, these items would be shown on a
printout of the tune volts etc at each plug output of coil,alternator etc,
also do a compression test.

DAVE R

 

HI,
what year is your fiesta does it have a throttle switch fitted,

DAVE R

 

I checked the dizzy and cap and rotor, fuel pump was ok last time i checked about 3 months back, i checked the coil about 3 months back and it seemed ok i test it again. i managed to get it half better i weakend the idle mixture, since it does it when going from no throttle to putting some throttle on, it seemed a lot better and this was testing it tonight in the cold damp weather on a 5 min run so it might be ok know when the engine warms up on a propper run

Its a F reg mk3 1.6s not throttle switch. just the TLD carb.