Have you tried cleaning out the exhaust screen? Sounds to me like the screen is plugged, its a real easy thing to do (cleaning it out at least).

 

I'd check the screen first, as mowerbrad suggests, and make sure you are not over mixing the oil to fuel ratio. It should be 50:1 using a good quality 2 stroke non marine grade oil.


.... and check to make sure that the filter is down at the bottom of the fuel tank where it should be. Sometimes they get traped in an awkward position up at the top of the tank, and when you bend over it doesn't take in all the fuel it should to keep things running correctly.

 

The fuel is fine , I have been doing it and using the same stuff for years , I am going to replace the spark plug and filter and see if that works. I did take it apart and clean it.

 

The fuel is fine , I have been doing it and using the same stuff for years , I am going to replace the spark plug and filter and see if that works. I did take it apart and clean it.

How did you clean the exhaust screen? I have a BR340 that I've had for years and it did almost exactly what you described...when I was using it, it would only get up to about half throttle or a little more, it didn't cut out that I can remember though.

When I first cleaned the screen, I just figured I'd rinse it out with water...thought that would get it cleaned out well enough. However, I soon learned that you have to take a flame to it to get it cleaned out nicely. So, I took out my propane torch and put the screen on the driveway and went at it. A few seconds later I was done and ready to reinstall the screen. Once I replaced the screen, it was running like new again. Amazing what a few seconds with the torch did for it.

I don't see your problem being an issue with the spark plug, unless you are having difficulty in starting as well. Your air filter may be clogged, but I'm guessing its the exhaust screen still.

 

I don't see your problem being an issue with the spark plug, unless you are having difficulty in starting as well. Your air filter may be clogged, but I'm guessing its the exhaust screen still.

I am still in agreement with brad here. I seriously doubt that you have any problem with the spark plug. It never hurts to have a new air filter but I doubt that is it either. Take the screen out and clean it good. Different people have different methods of doing it. Here's mine-
Take it out and soak it in a god cleaner like Gunk. I have a quart can of the stuff that I bought many years ago, and it came with a parts bucket inside the can when new. I drop the screen in the bucket, let soak a little bit while I do other maintainence, or eat or something. Then I take it out, lay it on a flat clean surface, and use a small brass bristled brush like the ones they sell at Harbor Freight, Lowe's, ect., and scrub it down while still wet with Gunk. It doesn't take very long to have it looking like new.

One other thing to check (though I still believe it's the exhaust screen) is the fuel line. I have had them get old and have a weak spot in the wall that would collapse inward and cut off flow when more and more throttle was applied, but when I let off on the trigger and there was less draw from the tank, it would expand back outward and allow the fuel to flow again. I couldn't figure that one out 'til someone else told me to check for that and sure enough!