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I am attempting to repair a BR700 backpack blower for a friend. My friend brought it to me saying he had it looked at by a local Stihl dealer..who told him it was tied up and needing major engine repair. I removed the spark plug and put an oz. of ATF and a little gas in the spark plug hole…worked the crank back and forth a few degrees at a time, and it came loose. I reassembled it and it started and ran. It re-starts.
What I am experiencing is a situation where it will run for 5 minutes at full throttle and then it will seem to lose power. It runs so good for the 5 mins. it’s hard to believe that t there is an internal engine problems. I have not removed and or cleaned the carburetor, but I have tried to adjust the low and high speed needles and I just don’t seem to be able get it adjusted to rev fmsmoothly or so

Cfs said:

I am attempting to repair a BR700 backpack blower for a friend. My friend brought it to me saying he had it looked at by a local Stihl dealer..who told him it was tied up and needing major engine repair. I removed the spark plug and put an oz. of ATF and a little gas in the spark plug hole…worked the crank back and forth a few degrees at a time, and it came loose. I reassembled it and it started and ran. It re-starts.
What I am experiencing is a situation where it will run for 5 minutes at full throttle and then it will seem to lose power. It runs so good for the 5 mins. it’s hard to believe that t there is an internal engine problems. I have not removed and or cleaned the carburetor, but I have tried to adjust the low and high speed needles and I just don’t seem to be able get it adjusted to rev fmsmoothly or so

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I hit the wrong button and sent the above before it finished…. So to get back too it I had the muffler off and cleaned the spark arrester screen and there is nothing wrong with it. I attempted to look at the piston through the exhaust port but it seems that this engine is the Stihl 4 cycle that uses 2 cycle fuel. I was unable to see the piston and determine if there was any scoring of the piston or a stuck ring. I assume that there is a valve lash setting that could be air of adjustment. I do have an electronic compression checker and I am reading 105 lbs with 5 pulls and 120 with 10 pulls. This isn’t fantastic compression but it seems adequate. I did notice that I removed the gas cap it seemed like there may have been a vacuum in the tank and it makes we wonder how the tank vents pressure? I do not see a vent like what I am familiar with Echo products that includes a hose stuck into the fuel tank grommet. How does this blower vent? I also noticed that the primer bulb did not seen to have a real strong pull and the bulb did not fill robustly. I am wondering if a fuel line or fuel filter might be an issue. I will probably pull the carb and run it through an ultrasonic cleaning and replace the pump and metering diaphragms.
So I am asking for any answers to the questions l’ve raised. 1. Compression is or is not adequate? 2. How does the tank vent and is it able to be checked? 3.what are the initial carb H L settings number of turns out?
Any and all input us welcomed
Thanks
CFS

Fuel Tank vent.

So I am not going to get a chance to try to fix this.. my friend called me and said the dealer had called him back and said that when they were looking at his records, they looked at the wrong blower and this blower was in fact under warranty. So he picked it up and is returning it to tge dealer for an in-warranty repair. I am going to ask him for a copy of the work order and see what the trained Stihl tech found and fixed.
Thanks for the help
CFS