Stihl BR450 runs very poorly

[ericm979]

My BR450 (two stroke) started running poorly and not revving out. I replaced the ~6 week old fuel thinking that was the cause but it still does it with fresh fuel. In fact it's worse, it will barely rev above idle and idles rough. The piston looks perfect through the exhaust port. The carb is spotless inside but I blew the passages out with carb cleaner. Swapped in a new spark plug. No change. Starting to suspect an electrical fault. Ground wire is tight. The resistance between ground and the plug boot is about 65k. I don't have a BR450 manual but the MS460 says it should be 1.5-12k. Does it sound like the coil (or plug wire)? Are there more diagnostics I should run?

 

[ericm979]

My BR450 (two stroke) started running poorly and not revving out. I replaced the ~6 week old fuel thinking that was the cause but it still does it with fresh fuel. In fact it's worse, it will barely rev above idle and idles rough. The piston looks perfect through the exhaust port. The carb is spotless inside but I blew the passages out with carb cleaner. Swapped in a new spark plug. No change. Starting to suspect an electrical fault. Ground wire is tight. The resistance between ground and the plug boot is about 65k. I don't have a BR450 manual but the service manuals for MS460, MS362CM and MS660 all say it should be 1.5-12k. Does it sound like the coil (or plug wire) is bad? Are there more diagnostics I should run?

 

[Aknutter]

Did you check/clean the screen on the muffler? Google an ipl for your br450 and look at the muffler. Should be able to look at where the exhaust shroud is, there should be a screen under the snout that is plugged with carbon

 

[ericm979]

I'll check that, thanks.

 

[ericm979]

Wow, that worked! That's the first time I've had a screen clog like that. The design seems like it'd be easy to clog. Thanks!