10 replies to this topic

[madminidave]

hi all,
i have had loads of problems with my mini most of them fixed now but one! missfire and backfire
it started off as a missfire, backfire and popping on every road trip but just a few times and also when going round corners fast
i did all the checks and found my plugs were in a mess and the twin carbs oil pots was low so i topped them up
ran kind of well for a week then the same problem, it got worse so i checked and removed the fuel pot on the carb (fuel in) and found the pot was coverd with scale and soil in the bottom, i gave it a good clean and while checking the pistons i found they were sticking in the piston housing with score marks so i rubbed them until they were smooth and the pistons were moving freely (both of them) put it back together and she was running loads better and was only the odd miss and backfire
i then decided togo to tms and get some new plugs and while i was there i got new points, condencer, a rotor arm and a inline fuel filter which was not on the car
fitted the new plugs and the car was running the same i then fitted the new points rotor arm and condencer and she was running even worse popping and backfire from tick over and reving so reset the points and was still the same
i then replaced the new rotor arm with the old one and job was sorted she ran near perfect just the occasional miss and pop but better than before
a week later i was driving flat out late for work and she gave up first started with a big pop and then a backfired and missfired till i costed it into a layby and she cut out on idle. like when its raining and the dizzy gets wet
looked round and could not see any problems checked the dizzy and it was clean and dry, about 15 mins went by and she started back up and ran great but still with a slight miss and pop
but now everytime i go out in the car she gets worse and worse when she gets worm she starts to miss and then cuts out
i decided to check all the earths and they are fine
replaced the condencer with the old one and its still the same
now i only have to drive 5 miles before she breaks down
i have noticed on idle she does a cupple of slight pops in the exhaust and im not sure if this is normal but sounds wicked!
i have also notice that it misses more on cold with the choke on and then clears out when shes wormed up then starts missing and popping when the throttle is halfway
she drives a lot better on full throttle until she gives up and i have to find the nearest place to pull over and give her a rest before moving off, also the jurneys are getting shorter and shorter before the problems start
ive checked all wireing and there fine
can anyone help???

[orangeboy]

did you replace the dizzy cap?
also did you clean out the carb float chambers? if the carb needles arn't seating the carb could be flooding at full throttle

[petey81]

sounds like coil mate, coil breaks down after it overheats then its ok once cooled down.
you have changed all the main parts. have you checked the main jets and line between float bowl and jet?
what oil are you using? and how much you topping it up?

[jmmini]

I had a similar problem, think is a good call from Petey there, I changed my coil and shed still running fine a few weeks later

[longbridge4life]

Could be coil plus you've not mentioned doing your tappets. That'd be a great start checking your tappets are properly gapped it certainly helped mine. I set my exhaust gaps to 15 thou and inlets to 12 thou on my 998cc A+ engine.

[jakejakejake1]

I had a problem recently, where if i dropped below 2000 rpm the car would cut out and it was due to dirt and crap being pumped into the carb, and at low throttle it would jam up the carb and cause such a lean mixture that the car would make loads of funny noises and cut out.
A full throttle blast for about 5 miles or so after filling the tank sorted it for me.

Also double check all the simple things like valve clearances, points gap, plug gaps, dash pot oil, ignition timing, idle mixture & balanced carbs.

[madminidave]

i have cleaned my dizzy but not tryed another one but will do soon as i can afford one as i have ran out of pennys
i have a spare coil to try tomorrow and see if there is any diffrence
the carb has been stripped down and cleaned and float chambers cleaned but i put 2 stroke oil in the pots so i will change back to 20/50 and give that a try
when cleaning the carbs i notice score marks on the big piston and chambers they were a slight grinding noise when moving them in the chamber so cleaned them and they were a lot better, layed them on the floor with the springs in and let them off at the same time and one was slightly faster at popping out than the other but when lubricated with oil they were near the same, fitted it back on the car and was much better then and drove good for a week
one thing i have noticed that when i lubricated the big pistons with a little oil and in the chamber the car ran sweeter until the chamber dried out (i have done this a cupple of times and has sorted the missfire a little) so i think they might be a little sticking going on would this cause me my faults i noticed the dash pot oil doesnt lubricate the big pistons ;( but then i seem to have a bigger problem cause the car now drowns and cuts out on me whick never happend before.
today i went to work and started my jurney which took 15 mins in total
i started the car up fine with the choke on but noitced i dont need it on as long as i should (the odd missfire still there when cold) normal i think
then while driving at any speed i notice the odd pop or backfire coming from the front id say the manifold or maybe inlet/carb area
and this also happend when changing up gears as soon as i put my foot back on the peddle but not all the time
and also drowning sounds and loss of power near the end of my 15 mins drive then cut out or clear out which ever it decided to do on that day
i can also smell petrol in the car when my problems happen, could be over fueling and causing the miss or because of the miss she starts to over fuel and smell not really sure
the engine is a mg metro 1.3 with twin carbs and 998 points
when i bought the car off the previous owner they now say there was the odd pop but never broke down and was only on a few jurneys

[petey81]

i would stick electronic ignition on it mate and run the metro dizzy with the module and power curve. or try accuspark.
sounds like you need to get it on the rolling road.

[madminidave]

i know but im skint at the mo
it did run right for a week lol

[bmcecosse]

Although I say it's 'never' the coil - in this case - I would certainly try another coil - but change NOTHING else at the same time and report back. It could be a problem with the resistance wire feed to the coil.....breaking down as it heats up. You could temporarily run a direct feed to the coil and try that - but don't run like that for any length of time because it will overheat the coil.....

[madminidave]

try the spare coil i had today and problem is now fix! she runs well with no backfires no pops and no splutters or drowning
thankyou everyone for pointing my in the right direction you have save me a lot of hassle thanks again ;)