I have a Briggs 18 horse twin motor. It will not start and is backfire a flame through the carb. I checked the valves ( adjusted to spec and pushed down on them and none are stuck. Trying to figure out how to get my motor running.

Hi all, my SRM230 Echo trimmer would not start after long storage period. Put in fresh gas, no go. Spark plug was dry and looked pretty clean so left it alone. Put on new air filter, new primer bulb, new fuel lines, new pickup filter, checked exhaust port for carbon buildup, it was clear, cleaned carb twice, second time took high jet out and cleaned it. I think the hi jet is where the problem was, could not get a fine wire through hole in tip to pass up where the hole in side was. Soaked it in carb cleaner 30 mins, poked at it some more and finally with the help of a lighted magnifer was able to see the wire through the side hole when poked through the bottom hole. Trimmer now starts and when warmed up some will idle fairly well, but when throttled up, it bogs and stalls out. No fuel or air leaks noticed. If I start it at wide open, it seems to run strong. So the problem is using throttle to move off idle to full cutting speed. What am I missing?