Stihl blower won't keep running.

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  #1  
Old 06-12-10, 06:57 PM
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Stihl blower won't keep running.

I have a 13 year old BR400 Stihl leaf blower. It will start and run, but sounds like it is starving for fuel. It will run for a short time (anywhere from 5 mins down to 1 or 2 mins.) and then slowly shut itself down. If the choke is then set to on and you give it one pull it will fire. Then you turn the choke off and pull 3 or 4 times and it starts again. It has new (about 15 hrs) spark plug, new air filter and pre-filter, new fuel filter, new gasket between air horn and carburetor, new diaphram, and new metering needle (adjusted properly). I have tried adjusting the High speed and Low speed needle valves and the idle speed needle valve. I don't know what the starting point (for turns out from bottom) is and I don't know how to hook up a RPM meter to the engine. I have an old MAC meter that works if I knew how to use it on a small engine. I also don't have any tourque specs or RPM specs for this leaf blower. Any answers would be appreciated!
 
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Old 06-12-10, 08:32 PM
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Will it keep running (poorly) if you leave on half choke? What about the fuel filter?
 
  #3  
Old 06-12-10, 09:47 PM
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It has a new fuel filter and I haven't tried to do half choke. I will in the AM. What if it does run better on half choke? What does that mean is wrong?
 
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Old 06-13-10, 07:22 AM
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It means it is running lean or it is getting too much air.
 
  #5  
Old 06-13-10, 08:24 AM
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Sometimes the whole thing gets a little shaded with the choke in the picture. You be running lean and the engine dies because of it and the choke will kick up the fuel/air mix. But the choke will also crutch a weak/faulty fuel pump diaphragm.

So you're at a point of saying is the problem in the carburetor/vacuum leak where you have the fuel in the carburetor and the thing is plugged.... or is the fuel just not getting to the carburetor by way of the fuel delivery gizmos like the tank/lines/fuel cap/filter crank pulse or diaphragm.

For a gradual bleed down like that, you might check the fuel cap/fuel lines. If good there, set the idle speed so it will at least idle at some rpm, then go to the low speed and set it for good acceleration. Then go to the high speed and set it for max rpms at 3/4 throttle, then back to slightly richer where you have a light flutter to the engine. Then back to the low speed at idle throttle and set it for max rpms and go back slightly richer while still having good acceleration.

Then set your idle speed for a decent idle.

Always err on the rich side rather than the lean side. Slightly lean will give the impression the engine is running better because it's more responsive, but that is the setting that will destroy a two stroke.
 
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Old 06-13-10, 12:08 PM
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Thanks much Marbobj and tolyn ironhand. Glad you told me the info about running too lean. That could have been trouble brewing. Now I know the sequence in which to proceed with the carb adjustments. Before this I was just turning the screws a little bit each and not having any order to it, as well as no luck! I will take your advice. Thanks again!
 
  #7  
Old 06-16-10, 11:34 AM
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Found a different problem

I have a BR380 and it has low power. Idle was OK but when I accelerate the power only went to possible 50% max.
To do it short. I disassemble the whole engine and I find a crankshaft bearing broken and also the oil sealer.
I replaced the broken parts, I assemble it, and it runs OK now.
The main reason of loss of power was because the oil went trough the broken seal and the other bearing did not receive enough oil to run smooth so it start to get temperature and brake the crankshaft. I hope this help. Charlie
 
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