Backfires/ pops from exhaust

[UnclePennybags]

Hi, I have a new 80cc ebay kit and it works great and has plenty of power (it seems to be a long stroke and the head has those 9 studs). However it pops like crazy from the exhaust under light and mid load. It seems that it backfires when it is 4 stroking at low rpm. This Weekend I hope to check the carb, plug and cdi but I also noticed some black liquid residue on top of my head gasket. Has anyone had this problem or does anyone know why this might be happening?

 

[Gordy]

Please post some pictures, I have never seen one of these 2 stroke engines with 9 head bolts.

 

[UnclePennybags]

I meant it had 9 studs on the side of the cylinder not the head.

 

[robe]

Looks like four bolts to me. My experience has been the stock exhaust was to restrictive for it to start brand new. Took the cap off and it fired right up.

 

[UnclePennybags]

It starts and runs pretty good but it sound like a machine gun. It does not sound like a healthy backfire. This Weekend I'll send a video of it running

 

[markjs]

I meant it had 9 studs on the side of the cylinder not the head.

View attachment 212391

Pretty sure the casting "dots" on the side indicate it's a G4 or G something cylinder. A slight upgrade from the older style, with an upgraded port map.

 

[molash]

The popping is usually almost because of 4 stroking but can also mean running too lean but thats more of a bang, like a modified sports car but In this case its almost 100 percent because of the 4 stroking. Its normal under light load but if even during uphill pulls at low rpm I.e not so much throttle, low rpm but still high load, its 4 stroking you should firstly adjust the jetting then if that doesn't work you can advance timing via shaving woodruff key, however its critical to mention that the stock plugs might not work so well either due to incorrect gap or just a crap plug so I would replace with a good plug before anything else.