Help me get this BR400 running

Discussion in 'Mechanic and Repair' started by keith.mcginnis, Oct 29, 2012.

  1. keith.mcginnis

    keith.mcginnis LawnSite Member
    Messages: 55

    Well I had someone give me this Stihl BR400 blower that quit working on them. I'm not sure what that means.. If it died, or just wouldn't start one day.

    Anyhow, it a decent looking blower. I just can't get the bastard to run. Here is what I know and what I've done.

    Compression around 120psi
    Unit gets spark while using my spark tester My Spark tester
    Tries to run after a little starting fluid (with upper cylinder lubricant)

    What I've done:
    Checked Flywheel and key - Magnets were strong, key not sheared
    Regapped coil
    New NGK Plug
    Soaked Carb in Seafoam and replaced diaphragms and pump
    Checked Carb mounting flange/spacer for cracks and replaced gaskets
    New Fuel Line
    Checked Fuel Filter
    Removed spark arrestor screen
    Removed muffler and torched the inside

    What really puzzles me as I try to troubleshoot this blower is, Spark always test good (according to my method) and the plug always seems wet and smells like fuel after cranking. My first inclination when I got this blower was the coil, and I still don't trust it. But if the coil was bad would the engine run for a few seconds on starting fluid? What am I missing here?

    Should I replace the Carb? Coil? What does everybody think? I really appreciate everyones help. I can link you to a Parts Guide and Service Manual if needed.

  2. RussellB

    RussellB LawnSite Fanatic
    Messages: 8,748

    Are you sure the on/off switch works?
  3. keith.mcginnis

    keith.mcginnis LawnSite Member
    Messages: 55


    Thanks for the help. The only reason I know that it works is because it sparks on the tester to ground and at the plug when grounded. When in the up position.

    Does a wet plug necessarily mean the carb is functioning properly?
  4. dhardin53

    dhardin53 LawnSite Senior Member
    Messages: 710

    Check closely the spark arrester in or at the end of the exhaust hole. This screen will get just slightly clogged and cause a hard to start issue (or run for a short time and stop).
  5. dhardin53

    dhardin53 LawnSite Senior Member
    Messages: 710

    Sorry is did not see you already address the spark arrestor issue.

    Notorious for hard to start, when cold ALWAYS start with a full fuel tank, a full tank aids in the amount of pulls it take to get gas up to the carb. Some guys i know will turn blower on it side till it starts to fire.

    Also get a large rubber band to hold the trigger throttle wide open, Some say this helps. This is some of the issues with a wet plug, when starting at a near ideal the fuel to air mixture is going to get the plug wet if at ideal. It don't take long for even a new plug to foul out if you continue to trying to start. Once you have a very wet plug. STOP let it dry out some and then continue. This is why the rubber band trick CAN help in some cases.

    Starting fluid has a higher flash point making it easier to start but not run with a fuel mix. Your mix may have to much oil in it. for now try a lighter mix of oil to gas mix.
    Last edited: Oct 29, 2012
  6. keith.mcginnis

    keith.mcginnis LawnSite Member
    Messages: 55

    Now that you say that. It doesn't have very much fuel in it. Ill put some more in it and try that.

    I also tried the throttle wide open trick, to get some more air in the cylinder.

    I didn't mention before, that did get it running 1 time. Randomly, for about 2 mins. It never would clear up. Once I shut it off, It would not fire again.
  7. keith.mcginnis

    keith.mcginnis LawnSite Member
    Messages: 55

    Is it possible a weak coil may fire with the starting fluid, but still be a bad coil?
  8. BigFish

    BigFish LawnSite Platinum Member
    Messages: 4,192

    Yes. Most Stihl coils have a built in rev limiter, that when heading south, can cause an intermittent spark etc.
    You also want to make sure the fuel line is in good shape and the primer and lines are good.
    But I think you'll find the coil has taken a dump.
  9. dhardin53

    dhardin53 LawnSite Senior Member
    Messages: 710

    Possible. Judging week coil is difficult. Most usually if its a weak coil it will start but not restart. The coil gets hot or warms up and then fails. If you have a multi tester meter you might test the Resistance of the coil. This can also be misleading, the amount of spark can look good but not be enough to spark after 10 to 30 good sparks then fade away..

    If you have done all other checks a new coil could be your answer. But in the mean time there is a few more things to check.

    You said you have good compression, but you may have out of adjustment valves causing the combustion timing to be short.(you have good compression) poor compression is valves staying open to long, or burnt/bad.
  10. keith.mcginnis

    keith.mcginnis LawnSite Member
    Messages: 55

    I did replace the fuel line, but this model does not have a primer bulb. I wish I had a good know coil to test with. Kind of hard justifying a new coil if i'm not 100% sure that's the problem.

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