Older bike won't start-- popping sound but nothing else

[thelordandmasterof1410]

Good evening all,
Just picked up my first motorized bike today, and was disappointed when I got it out on the pathway to find it wouldn't start! Fiddling around with the choke/idle and priming the engine again didn't help, so I headed home and tried a few things:
- Checked the air filter- clean and no passages blocked
- Checked drive chain tension- looks good, about a half inch of play
- Checked clutch engagement- also seems good- engine is not at all engaged when pedaling, but I can feel it's resistance when engaging the clutch.
- Gas valve is open and fuel is flowing

So now when I get moving and engage the motor, the engine whirrs in what sounds like a decent idle. Opening the throttle changes the pitch to a bit higher. Intermittantly (about every 2 seconds) the engine makes a popping noise (fires?) and I feel the bike shudder forward a bit. As soon as I stop pedaling and coast, the engine trails off until I have to disengage the clutch to keep moving.

-No warmth to the engine or muffler
-No smell of fumes

Tomorrow I plan to check the spark plug (no access to my sockets tonight). Any other suggestions?

 

[Vikingimike01]

Could be a big air leak, and it's so lean it won't go. Test the head gasket and intake gasket for leaks, with some soapy water, then turn over the engine

 

[Chainlube]

The very first thing I do when I buy a used machine, is pull the carb off and clean it out. The float bowl, float, float needle all need special attention. Blast through the main jet with some brake clean, that'll make sure it's clear. While you have it off look at the position of the clip on the main jet needle, move it to the second from top if it's not already there. Then it's just a matter of checking that everything is tight, don't try to make them too tight, alloy parts strip under gorilla pressure.