Stihl BR420 High Throttle issues

Discussion in 'Mechanic and Repair' started by ricrawling, Nov 8, 2009.

  1. ricrawling

    ricrawling LawnSite Member
    Messages: 8

    Good morning everyone. This is my first post here.

    I am having a problem with my Stihl BR 420 Backpack Blower. It starts and idles fine, but at high rpm, the only way I can get full power is to adjust the choke slightly (towards starting - closed position).

    I have checked my air filter (even tried to run for a minute without the filter on) and have checked the screen on the muffler, and neither seem to help.

    I have also tried to adjust the H and L and TA set screws on the carb, but no help either.

    If anyone else has had this problem or has an suggestions, please let me know. I am not super mechanically inclined, so please excuse me if I am not giving the appropriate mechanical terms.
  2. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,586

    Remove the screen, and check the gas fuel filter and put in a new plug. How old is the unit?
  3. ricrawling

    ricrawling LawnSite Member
    Messages: 8

    I have had the unit about 6 years, so the unit is around 7 years old. The only thing I have done is replace the spark plug a couple of years ago. I am a residential homeowner, so probably only use the unit 10 or 15 minutes a week except for the few times in the fall I have to blow leaves.
  4. Pro-Scapes

    Pro-Scapes LawnSite Platinum Member
    Messages: 4,180

    Couple things.

    The high side is most likley lean. When the air cools down for the year it becomes more dense. Its common to need to adjust your carbs seasonally in some areas. You mentioned adjusting your high and low speed needles but do you know what you are doing or did you try the turn and pray version of it ?

    Another possible cause is trash in the carb. You could very realistically need the carb rebuilt. My advice is take it to the stihl dealer and let them fix it right. You tried the basics and it didnt work out.
  5. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,586

    Try running some sea foam adder into the gas.. And they make a spray that can be shot into the carb.

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