backfire indicates a lean mixture condition. I would also be checking the idle cct for the cylinder that is not firing. No fuel = not firing. I would also check the balance between the twin carbs, i.e are all 4 throttle plates opening in a synchronis way. And lastly, see if the progression holes are blocked or not, this can also induce a lean mixture.

i'm using twin 40's..
1 wasnt firing..it only firing at hi rpm,but still have the backfires..

neway thanks for the advices..

will recheck the carbies again

thanks you very much

1. Remove all air filter bases and horns. Test it like this before putting air filter back on. Mine had the wrong base on it, caused really bad performance and backfiring. I could still do 120 kph though.

2. Make sure the Starters (chokes) are rotated all the way -- they can cause weird coughing and backfiring if out of sync with each other.

du u mean twin 40's ?

1 throat/jet not working, blocked would explain 1 cyl not firing on idle, the main jets work but not idle jet on that throat.
backfires if u havent changed anything else might be its over jetted if u havent got cam, exhaust, ignition to cope with the extra fuel.

i think what he means is that it was down 1 cyl or in other words 1 wasnt firing

what u mean 3 pistons running at idle, if a piston wasnt moving then changing the carb wouldnt make it go again, sounds like broken piston/rod/gudgeon pin ......

Hi guys,

need ur help and expertise here..

just installed Solex 40 to my a14..but i'm facing 2 problems which is giving me a headache :-

1. Backfire in the carb
2. Only 3piston running when idle

when i change back to the old carb (downdraft) ..it all went well..nothing wrong..

what caused the problem?

thanks.
amin