Nissan 1400 Champ. What is causing it to backfire and jerk?

Have you checked the timing marks on the timing gears?

limited info generic answer fuel delivery -weak or failing valves--coil failure--bad fuel -needs complete tune up --timing

Question edited for clarity.
Question moved to Nissan.

There is some ideas in the link, but you need to find someone in South Africa that has a scan tool computer. Dirty injector from bad fuel is the most likely. Check the spark plugs as well.

https://www.google.com/search?q=2008+Nissan+Champ+1400+is+jerking+and+cuts+off+when+I+accelerate+to+50+kph

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i think the best solution to solve the problem is service and repair manual which will help you locate and fix the problem by your own and you can get the manual from the given link http://toolsnyou.com/

similar problems: After 20min cool down jeep was bucking/lurching that I traced to bad o2 sensor in exhaust manifold (which you've replaced is seems). The second problem of bucking/lurching, backfiring under certain driving conditions I traced to the battery sliding into the computer wiring harness, disrupting sensor input / output signals. I cured this problem by placing a 1" spacer on rear battery clamp, pushing the battery forward. Been years and no return of problem.

hi, personally ..i love that bakkie. Ok you changed points condensor, petrol filter! please check.. When it cuts out 1. if the ignition coil is not hot, if so thats your problem.2. also on the carb... over the needle and seat there is a tiny filter... somtimes gets blocked. 3. also check when it stolls if the fuel pump is not hot or pull the outlet fuel from the pump
and crank the engine... note if fuel comes out sufficiently.

carb float is sticking

Here are the common cause of surges, stalls at stops, slow idle speed, erratic idle, it is in most cases the idle speed control air-bypass valve and/or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving

check compression is it more then 10% difference between cylinders you have a leak also check for fouled plugs. wires fuel pressure, catalytic converter. i have the same problem in my lincoln its a leaking valve seat

That could be caused by anything from engine or transmission control problems to broken engine or transmission mounts. I would recommend taking it by your local auto repair shop and having one of the techs drive it to give you a better idea of what could be causing your problem.