Stihl Blower.. spark and compression but will not fire at all. I am getting P****!

Discussion in 'Mechanic and Repair' started by summej, Feb 12, 2011.

  1. summej

    summej LawnSite Member
    Messages: 16

    Have a Stihl BG 55 handheld. Has plenty of compression good spark with plug out. I CAN NOT GET IT TO FIRE FOR ANYTHING with plug in!!

    Anyone know how to properly set the gap on the flywheel and ignition coil?

    Also I am thinking that maybe the flywheel key spun?

    I am trying to start with starting fluid... sprayed a lil in plug hole-nothing
    sprayed a little in carb throat....Nothing. No Fire either time

    Cleaned carb.

    I am going to dump the gas and ad fresh 93 50:1.
    running out of ideas...
    Any suggestions

    How do I check/set the flywheel timing?

    It appears to me that Stihl USA locks down the PDF repair manuals tighter than the The National Security Admin. /NSA.
    They want us all to go to the dealer/steelerships
    Maybe I will call Wikileaks.
  2. jkilov

    jkilov LawnSite Bronze Member
    from MS
    Messages: 1,415

    First of all this is not a proper spark test. Under compression air is about 9x denser, a better insulator and may prevent the voltage from sparking.

    It does sound like an ignition issue, check the key, flywheel gap, and measure the resistance of both primary and secondary circuits on the ignition. If unsure have a dealer do a spark test. Some stihls have a programmed timing ignition module, these sometimes get stuck in advanced mode making them impossible to start. I'm pretty sure the bg55 does not have this type.

    A good redneck spark tester: leave the original plug in, connect the lead to a second, preferably non-resistor plug with minimum electrode gap and ground on original plug. If the coil manages to spark both plugs it's definitively good.
  3. ricky86

    ricky86 LawnSite Silver Member
    Messages: 2,142

    "Since there is no mechanical wear
    in these systems, ignition timing
    cannot get out of adjustment.
    However, an internal fault in the
    circuit can alter the switching point
    in such a way that a spark test will
    still show the system to be in order
    although timing is outside the
    permissible tolerance. This will
    impair engine starting and running
    This above quote is out of a BG55 dealer service manual. Translation is, you might have to try a new module to rule out an ignition problem (if, in fact, it is an ignition problem). Spark testers can't help if it's a timing issue. You can, if you're capable, hook up a timing light to it. If It fires ATDC (after checking flywheel key), you found your problem. One word of caution: that crankcase is most likely filled with fuel and starting fluid Watch out pulling the rope. If it ignites, and you face is in the way...........
  4. onlythebest

    onlythebest LawnSite Senior Member
    Messages: 536

    to set the gap i believe they have 2 or three screws holding the ignition coil loosen maybe 1/2 turn and set the gap to 0.014 across both sides of the coil then tighten screws and check again... had to change all three of my sh56 blower vacs
  5. summej

    summej LawnSite Member
    Messages: 16

    I removed the flywheel and the key does appear to be worn. Stihl does not have the traditional type of flywheel key that slides out-it looks to be formed onto the actual flywheel... looks like a crush key. I think the flywheel may have spun a little on the shaft.

    I am still able to tighten and adjust the position of the flywheel in relation to TDC.

    Question: what position should the magnetic pickup be on the flywheel when piston is top dead center? In other words.. the plug needs to fire at TDC. The coil needs to be firing then too correct? there are two obvious pickup/ firing points on the coil-one in the center of the coil and one 1" below it. I need to know where my firing point is on the coil in relations to the flywheel.
  6. ricky86

    ricky86 LawnSite Silver Member
    Messages: 2,142

    Do you know anyone who has a BG55/65/85 ? If so, swap coils. Your engine fires BTDC (about 5 to 25 degree's depending on RPM). There are no hard spec for what your looking for because it's considered fixed, meaning non- adjustable.. With a light on it, if it's firing 90 degree's after TDC, then you have a problem. Those modules had a 5 year warranty on them. Is your's older? I'm telling you again, if everything else checks out, you will have to replace the module to rule out a ignition problem. The list price is about 30.00 (29.50} to be exact
  7. jabirt1

    jabirt1 LawnSite Member
    Messages: 7

    Maybe it's not ignition?

    Check the spark arrester, muffler and exhaust ports. If they're carboned up--especially the spark arrester screen--it will not fire.
  8. BigFish

    BigFish LawnSite Platinum Member
    Messages: 4,194

    If you can move/rotate the flywheel on the crank,even a little bit, then your screwed!!
    You either need to replace the flywheel or the crank.
    Pay attention to WTF people are telling ya!!
  9. StihlMechanic

    StihlMechanic LawnSite Bronze Member
    Messages: 1,133

    Have you removed the exhaust to inspect the pistion? If its scored/scratched its junk. Also, you mention it has comp, how much psi? You need at leat 120.
  10. dboyd351

    dboyd351 LawnSite Bronze Member
    Messages: 1,126

    I'm no expert mechanic, but if it won't fire at all when you shoot starting fluid in the intake, or the cylinder, I don't see how you can have spark.

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