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How To Perform Governor Adjustments on BBC Mowers

Discussion in 'Mechanic and Repair' started by OldLawnMowerMan81, Jul 3, 2012.

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  1. OldLawnMowerMan81

    OldLawnMowerMan81 LawnSite Member
    Posts: 66

    Has anyone ever tried to make any governor adjustments on any lawn mowers as equipped with the BBC?

    My 1984 Toro 20672 is one of those mowers that are equipped with the BBC. The governed high speed, according to Toro, is between 2800-3200 RPM, which I believe is with the blade engaged. If the median is 3000, then with the clutch on (blade is not spinning), that would be closer to about 3100 RPM or so.

    And my question is thus: What would I do to check the engine speed, with the blade spinning (meaning you c*ck the bail bar toward the engine and then back toward you, to spin the blade)? The tone and pitch of the engine will be slightly different with the clutch engaged (blade is disengaged, or not spinning). This is truly a two-man effort if you wish to do so with the blade engaged.

    So, folks, what do you do to determine the engine speed, blade engaged vs. blade disengaged?

    ~Ben
     
  2. cgaengineer

    cgaengineer LawnSite Fanatic
    Posts: 15,782

    Generally the rpms are set at no load which is called high idle.
    Posted via Mobile Device
     
  3. OldLawnMowerMan81

    OldLawnMowerMan81 LawnSite Member
    Posts: 66

    So, even with the blade disengaged, then, if I were to measure the governed speed using a tachometer (TinyTach, for example), it should still read 3000 or so tops, correct?

    Likewise, most Honda lawnmower-size engines (GV150, GV200, GXV120, GXV140, etc.) are governed for 3100 RPM tops, with a marginal error (the plus/minus constant) of 100 RPM (3000-3200 RPM). That is, if any of you mechanics are familiar with and/or have preferences to this term.

    ~Ben
     
  4. cgaengineer

    cgaengineer LawnSite Fanatic
    Posts: 15,782

    Correct. When put under a load the gov will adjust the speed back to 3000-3200 rpms.
    Posted via Mobile Device
     
  5. dutch1

    dutch1 LawnSite Silver Member
    from Jayhawk
    Posts: 2,231

    That's a revelation to me--that Toro ever produced a BBC that was Tecumseh equipped. I spent 7 years in a Toro shop from the late 90's to the early 2000's and never saw one in the shop. Rather surprised that a Tecumseh of that age is still running--you must have given it exceptional care.

    It's just me but I would set it at 3000 under load(blade engaged) and be done with it. On the other hand, if you're still on the unaltered original engine, leave it as it has been.
     
  6. OldLawnMowerMan81

    OldLawnMowerMan81 LawnSite Member
    Posts: 66

    The engine I have on my '84 Toro is the original one from the factory.

    But my next question is this: has anyone tried to bend the governor spring whilst the engine is running? This is where it becomes a two-man job: one man would be holding the handle bail bar (so as to verify the top speed with blade spinning), and the other would be performing governor adjustments.

    ~Ben
     
  7. piston slapper

    piston slapper LawnSite Platinum Member
    Posts: 4,240

    Ben...I'm sure it would be safer adjusting it that way....but...
    In the mower shops...we just tie down the handle bail....and adjust it...
    I usually use a big spring loaded clamp....

    BBC..???..When did they put Big Block Chevys on mowers....?
    Missed that day in school....
    Posted via Mobile Device
     
  8. OldLawnMowerMan81

    OldLawnMowerMan81 LawnSite Member
    Posts: 66

    What I meant to say is this: my engine is the TNT100. On this series of engines, to increase the speed you will have to bend the tab (for which one end of the governor spring hooks to) leftward; to decrease speed, this same tab is bent forward.

    It is actually not recommended to bend the tab back or forward whilst the engine is running because you may risk burns from the hot engine. Also, it is not recommended to tie down the control bar for safety reasons.

    Also: I wanted to know whether or not the #670326 governor adjustment tool Tecumseh supplies actually works with the TNT100 and TNT120 series engines.

    ~Ben
     
  9. dutch1

    dutch1 LawnSite Silver Member
    from Jayhawk
    Posts: 2,231

    I just pull out the recoil rope and wrap 4 or 5 overlapping wraps around the handle. I didn't take the time to look at the gov speed adjustment--Tecumseh used several different arrangements but apparently you have that covered.
     
  10. OldLawnMowerMan81

    OldLawnMowerMan81 LawnSite Member
    Posts: 66

    BBC = blade brake clutch

    ~Ben
     

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