Stihl Br600 bogs down

[dirtbiker71]

I have a stihl br600 blower. it was running fine and then started to act up,was acting kinda boggish and was only running at about half the power. I found out the carburetor had came lose. I retightened it and still ran the same. then I tried a different carb which didn't help. so then I tried a different ignition coil and spark plug and still not running any better. I decided to do a compression test and it was at 130 lbs. this motor was just rebuild and was running great after the rebuild? what could be the problem?

 

[alderman]

Check to see that the spark arrester isn't plugged.


Sent from my iPad using Tapatalk

 

[dirtbiker71]

I checked the spark arrester and it was clean. I'm wonderin if the valves got burnt from to much air gettin in the air intake from the carb being lose and need to be replaced. I guess I should tare it all down and reopen the motor again and see what I got.

 

[ANewSawyer]

Carb came loose sounds like it may have suffered a lean condition. I hope you don't have a burnt exhaust valve or scored piston. What was part of the engine rebuild and did you rebuild the carburetor?

 

[dirtbiker71]

the carb was a new cheap after market. I'm wonderin if because it was a aftermarket carb if that has something to do with it running bad all of a sudden? the piston was a little discolored but I thought it still looked ok. the smaller valve had some carbon build up on it but I didn't think the valve it self looked that bad. if the motor has good compression the piston color shouldn't matter that much. am I correct? I cleaned up the valve put it all back together again and it still runs bad. not sure what to try next.

 

[ANewSawyer]

Because it is a four cycle, you will have to do a leak down test but an automotive tester won't work. The pressure is too high. You need a special Stihl (read $180) leakdown tester. And if you are cranking it by hand to get a comp reading, the reading won't be accurate. The engine has a comp release at cranking speed. Paiging @backhoelover

As long as there isn't scoreing or a stuck ring, the piston color shouldn't matter. I would be looking at the carb and fuel line. A kink in the fuel line would do that. I would open the carb and clean it. There could be a piece of alum stuck in a passage. But you said a different carb didn't fix it?

 

[dirtbiker71]

The different carb I tried was another one of them cheap aftermarket carburators. I'm wondering if them aftermarket carbs are junk. it looks like where the model# was it had been scratched off. I bought more then one of them aftermarket carbs awhile back for spares that are suppose to be new. they look new but the model # I noticed were scratched off. makes me kinda wonder.

 

[lone wolf]

The different carb I tried was another one of them cheap aftermarket carburators. I'm wondering if them aftermarket carbs are junk. it looks like where the model# was it had been scratched off. I bought more then one of them aftermarket carbs awhile back for spares that are suppose to be new. they look new but the model # I noticed were scratched off. makes me kinda wonder.

I would wonder too about that. Not so sure a valve is bad with that compression you have there. Try a carb what else can you do? Is this all the time or erratic this problem the other thing I am thinking is coil.