Jonsered cs 2159C backfire

[Kerryd15]

hello,

working on a Jonsered cs2159c, will idle for a few seconds and die-seems to POP back through the carb as it dies. try to open throttle and the bogs and instantly dies. adding a squirt of gas when i open the throttle and it dies instantly.
Changed spark plug.
Tested spark- spark will jump a 3/8 inch gap.
Cleaned up flywheel and coil. reset coil clearance to .012
Flywheel key is not deformed or sheared.
pulled muffler- screen is clean. cylinder is not scored. piston not scored.
compression 150
this one has the metal clamp on the intake. i pressure tested the crank case and intake- no leaks on pressure or vacuum.
pulled and cleaned the carburetor. everything looks good and clean. diaphragms are very pliable. carb holds pressure. This has the Zama carb. it still had the limit caps before i took it apart to clean it.
impulse line is open, no kinks.
This thing has me baffled. On the side of the jug there are 2 covers with tamper resistant screws. Are there reed valves behind there? its getting plenty of gas as if i give it a squirt it dies.
Any help appreciated.

 

[huskihl]

The caps on the side cover up the transfer ports. If they aren’t leaking, there’s no need to remove them. Nothing serviceable behind them I would try some different gas. And unhook the blue ignition wire from the coil and try it. And inspect the spark plug wire. Sometimes they get corroded underneath the boot where the spring pokes through the wire.That would rule out a short in the wire or switch. Maybe try a different coil from another 3 series

 

[L34]

I had a similar problem with a Baumer Ag saw.
Turned out to be the coil.
Would start,idle then backfire and start running backwards lol.