"Chetzy... I assume you've
"Chetzy... I assume you've checked the compression and ignition. If not, it would be a good idea to do so. Compression should be up around 80/100 lbs and even on both cyls. Spark (with the s/plugs out) should jump a 1/4" gap on both cyls.
NOTE.... Use a 50/1 fuel/oil mixture. One (1) pint of 50/1 oil to six (6) gallons of gas.
If there are any fuel leaks at the fuel connectors, tank, etc, the fuel pump will draw air. Keep that in mind. The carburetor, if it's been sitting for (by what you said) a year or more, I'd strongly suggest that you clean and rebuild the carb. However, since it does run right now, you might try adjusting the carb needle valves.
If memory serves me right, that engine has adjustable high and slow speed needle valves. Gently turn both of them in until they seat, then back out the high speed needle (the bottom one) one (1) full turn, then back out the slow speed needle (top one) one and a half (1-1/2) turns.
I know you can't hold the engine at full throttle in gear in a barrel but you'll need to hit full throttle at various times to obtain a accurate setting. At full throttle, turn the high speed needle in until you hit a point whereas the engine starts to die out.... then back it out approx 1/4 turn to its smoothest setting. The final setting is usually about one half turn out but it does vary.
Now, out of gear, in neutral, slow down to where the engine will just stay runing. Start turning the slow speed needle inwards in 1/8 turn segments, waiting each time a few seconds for the engine to respond.... the rpms will increase. Again lower the rpms to a just stay running setting and continue the 1/8 turn procedure until the engine either starts to die out or spits back like a mild backfire. At that point, back that s/s needle out approx 1/4 turn to its smoothest setting. Hopefully all is well. Let me know.
Joe (30+ Years With OMC)"