Two stroke backfire when cold

[PotatoHead202...]

Managed to get the CZ through its MOT today.

However, on the way home it broke down 3 times (gurgled, bogged and died). Pretty certain this was down to very stale fuel that I stupidly used to top it up with (absolutely reeked). Washed the tank out, cleaned the (dirty) carb and managed after a number of kicks to get it running again. I'm getting what I'd describe as popping/backfire at idle for the first 20 or 30 seconds when cold. If I get on and ride it disappears and doesn't come back. If I normally start from cold it'll start with about 2 kicks.

Any ideas? Runs fairly well apart from this. I do have a suspected leak at where the exhaust joins the head and can see a bit of fuel leaking from the carb rubber to airbox join.

Again, this is basically a brand new engine and carb now with less than 30 miles on it. It has that crappy jikov carb so very basic. Getting a good spark and again this only happens when cold.
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Honda VFR1200F, Honda CBF500 ABS, CZ125 now CZ175

[MarJay]

crankcase is full of manky petrol and oil. My advice? Thrash it hard until it stops doing it.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[ThatDippyTwat]

[PotatoHead202...]

Aha, glad to hear that. I'll give it a dam good thrashing tomorrow!
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Honda VFR1200F, Honda CBF500 ABS, CZ125 now CZ175

[stinkwheel]

The spade terminals on the ignition coil can make a very poor/intermittant connection despite seeming tight so they are worth a try. A duff condenser could also cause issues like you describe.

As I remember they don't like resistor plugs either.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[PotatoHead202...]

Thanks, I'll have a look at the terminals as well just to be sure.

New exhaust bolt (wider flange) seems to have cured the backfire/popping. Have to be very careful not to flood it when starting from warm. The clutch is still the bane of my life at the moment - either too tight or too lose so it creeps in gear. Gearbox has to be the worst I've ever used, have to be really deliberate with changes or it either won't go in or will hit neutral, and that's with brand new selector forks and cam plate. Still could be worse, could slip out of gear.

Did get it up to about 60 yesterday though, gradually freeing up a bit.
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Honda VFR1200F, Honda CBF500 ABS, CZ125 now CZ175

[Nobby the Bastard]

[PotatoHead202...]

Tbf I was neck and neck with the other traffic on a fast A road that usually travels at that spped. I was somewhat shocked that I managed two (slow) overtakes on it!
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Honda VFR1200F, Honda CBF500 ABS, CZ125 now CZ175

[blurredman]