Exhaust popping issues after installing 150 cc big bore kit

Just wondering if anyone knows whats causing this,basically after installing the big bore kit i've noticed that the bike still starts first press of the button and sounds great but sometimes when i give it some throttle it cuts out and i need to restart the bike and other times its fine and runs very nice but when i de accelerate the exhaust pops! i havent changed my jetting so could that be the problem since its a bigger piston and bore not enough fuel getting to it?i'am still running the same stock pilot jet but my main jet is upgraded but not sure what size it came with the DEP S3 exhaust.

In my df250 the exhaust popped due to sparkplug gap to close and if it was to open the engine will shut off when accelerating or start bogging
I'm not sure this may help

Hmm ill double check the spark plug gap space,it's the same spark plug I used before I installed the big bore kit and all was fine so not sure if that's the problem but worth a try ! Thanks

In spite of the common believe that it is caused by a rich mixture, it is actually a lean mixture which causes popping on deceleration.

Your big bore kit is the surely the reason for it, now you will need to perform the balancing act to find the right (larger) jets.

You might create some other issues doing that though, it will be a very fine line to walk.

Thanks for the advice ! I've just ordered a 112 and 115 size main jets so ill give those a try and see if that resolves the issue,the bike goes great just a bit temperamental when I start it if I give throttle it cuts of but when it gets going its great till I slow down then the popping noise.Once I try the new jets if its still the same any ideas of what else would cause it ?

The air/fuel ratio is the most likely culprit, you will need to experiement with those jets. Also double check that the air filter is clean, as well as checking the timing. Make sure there is no exhaust gasket leak too or that it's not an exhaust leak from the headers. Check the nuts, if it's either loose nuts or an exhaust gasket leak, you should be able to hear the telltale "tat tat' if you listen for it from the head. Those compliant exhaust gaskets can handle lots of torque variance.

You might have to take the bike to a workshop that has a Dynojet.

When you suddenly close the throttle the incoming air is choked off and the closed throttle well cause the bike to return to idle on the lean idel circuit of the carbies. However momentum of the bike is actually "driving" the engine in a way, and the bike motor is still spinning at RPM that needs far more petrol than the closed throttle/carbie can provide. The motor is still spinning but the incoming fuel rate is low, until just enough builds up in the combustion chamber to 'fire' on the exhaust stroke of the motor.

To test this, the next time it happens, pull in the clutch lever and the popping should stop immediately, because the bikes momentum is not pushing the motors pistons to spin. You don't need to change the spark plug(s) since that just makes the plug manufacturer and seller rich. You shouldn't need to mess with the ignition timing, because it's still a lean air/fuel ratio on deceleration that is the root cause.

Try adjusting the pilot screws or you may need to go up a size or two on the idle jets. Don't go fiddling with those things before ascertaining whether or not the main jets are large enough. A good way to tell is to run it wide open in high gear. It should pull steady, if it surges or seems to miss, then you will probably need to go up a size on the main jets. For a fuel injected motor, it's much easier since one will probably need to have the computer remapped.

Summary: [Why This (normally) Happens]:

1). When the throttle valve is in the idle position, fuel does not flow out of the main system (needle, needle jet, main jet). Fuel is only delivered to the engine by the pilot (idle) system.

2). The combined effect of the closed throttle and elevated engine RPM is to create a fairly strong vacuum in the intake manifold. This vacuum, in turn, causes a high air flow rate through the small gap formed by the throttle valve and carburetor throat.

3). Under these conditions the pilot (idle) system cannot deliver enough fuel to create a normal, combustible air/fuel ratio. The mixture becomes too lean to burn reliably in the combustion chamber. It gets sent into the exhaust system unburned and collects there.

4). When the odd firing of the lean mixture does occur, it is sent, still burning, into the exhaust system where it sometimes ignites the raw mixture that has collected - the exhaust then pops or backfires.