Loud pop when trying to start motor

[ShayneCastonguay]

I have a 1978 mercury 200 20 hp that i just recieved. It needed a power pack, which i installed, and the motor ran for a little bit before cutting out, but did run. I pulled the carb and cleaned it all out (also replaced the plugs) only to find that the needle valve was sticking closed and no fuel was getting through. I recleaned the carb and adjusted the float, and fuel is now properly in the bowl. But when i pull the cord, i get a loud popping noise, not every time, but more than once. Occasionally, the motor runs one or two cycles and shuts down. Compression is at about 100 psi for both cylinders.

 

[guyjg]

The idle mixture may be too lean. The mixture screw should be turned out from full CW to about 1.5 turns CCW to start. If you did that then turn it CCW a quarter turn more. Spark is loud and snapping light blue?

 

[ShayneCastonguay]

Mixture screw? And yes. The spark is very solid.

 

[haventaclue]

Did you by any chance reverse the plug leads? I know I know but I had to ask

 

[ShayneCastonguay]

I'll check, I tried them both ways but ill try it again when i get home

 

[ShayneCastonguay]

Are you referring to the wires from the power pack to the coils or the ones from the coils to the plugs? I'm guessing the ones to the plugs

 

[haventaclue]

Yep,ones to the plugs,and I have to admit,I did this my self four weeks ago,

 

[fastjeff]

Welcome to the club!

Backfiring means the timing is WAY off. If the plug wires are correct, the spark advance must be off a ton.

Jeff