Several things .....

1) Clean or replace flame trap (my 245, which has a b230 engine also, had had the flame trap cleaned about 5 times but I still couldn't get it to run right. Spent 8 bucks, popped the new flame trap in and it improved the symptoms greatly)

2) Clean throttle body - this will also create problems if dirty.

3) Check all vacuum and intake hoses to make sure they are attached and in good condition. If vacuum leak exists it will smell rich but is actually running lean and you can burn valves or crack the head this way too since the 2 middle cylinders overheat

4) Replace air filter and make sure the housing is correctly fitted

5) Complete tune up including plugs, wires, coil, etc. Buy Bosch only. Kit is $28 from IPD.

Don't piecemeal on this one because if you run it too rich or too lean for too long you can start burning valves.

Good luck,

Richard Winn