HT engine problem

[Frankfort MB's]

I have a MB that has at least 1000-1500 miles on it that's been ported polished and matched with a tuned carb but the stock exhaust and it's about shot... When it gets about half speed it starts "machine gunning" at full throttle and won't go any faster, I thought it might be the cdi so I replaced it and still does it so I was figuring it was either magneto or crank bearings or piston rings, I only have 150$ in the entire bike so I figured I'd get rid of it for cheap (I don't like fixing 5 or 6 15$ parts on a engine that only costs 80$ for a new one) lol sorry that's such a long post
The only way I can explain machine gunning is that it starts popping like it can't rev any higher, btw I do run it without the baffles

 

[Frankfort MB's]

What should I do???

 

[crassius]

first, I'd loosen the muffler just a bit to be sure it isn't clogged - if no diff tighten it back up

next, I'd check for a fuel flow or mixture problem by opening drain on carb and watching flow when petcock is turned on, followed by a plug read to see if jets are clogged or needle in wrong notch

 

[Frankfort MB's]

I just tried both and it still did it, tried an entire other carb and it was unchanged

 

[Frankfort MB's]

I've tried different fuel ratios, with less oil it still didn't have any top end power, more oil made it worse, changed spark plugs, heads, spark plug wires, cdi, the bucking bar also has a lot of wear if that could be a problem? I've fooled around with these pesky things for about a year and I have went 43 mph on my buddies stock 80cc with a 32 tooth we still don't know how it ran so good lol he has no idea why my bike won't run no more than 25 with the stock 44 tooth being upgraded

 

[crassius]

clean it all VERY well and start looking for first place oil seeps out - could be loss of compression at case seams, crank seals, or head gasket

 

[Frankfort MB's]

It has a new head gasket and there isn't any oil underneath the engine and it actually has more compression than my other bike that will run 35 mph which is a brand new motor
It's a mystery that I might not ever solve like Bigfoot or women

 

[Frankfort MB's]

Tore engine apart and saw that the jug is a bad cast, I have piston blowby, and my base gasket is bad, how much worse could it be