Briggs 12.5 IC RPM problems

Discussion in 'Mechanic and Repair' started by MacGyver2, Sep 10, 2007.

  1. MacGyver2

    MacGyver2 LawnSite Member
    Posts: 2

    I have a Craftsman with a Briggs 12.5 IC Gold. The RPM's are out of control on this thing. I can adjust it to rev down a bit with the throttle all the way down. Once you add the slightest throttle it revs out of control. I'm waiting to catch shavings in my face. The carb is fine. It is clean and new fuel/air components are in. The mixture screws are adjusted appropriately too. The problem existed before the carb work but for how long I don't know. I think it is something engine related.....valves? Also where do you access the valve clearance adjustment. The manual leaves little to be desired. HELP MEEEE!
     
  2. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,022

    Sounds like you need to check the governor adjustment, Below is a post from another thread that explains the procedure. Also, What may be wrong if the adjustment does not solve the problem.

    Valves out of adjustment will not cause a over rev situation.

    http://www.lawnsite.com/showpost.php?p=1935261&postcount=9
     
  3. topsites

    topsites LawnSite Fanatic
    Posts: 21,653

    Engine will run, but it surges, hunts for a constant RPM

    1. Partial Blockage of Main Jet. This is for bowl type carburetors only. Stop the fuel flow to the carburetor, either turn off the fuel valve or pinch off the line with a pair of fuel line pinch off pliers or a pair of vice grips. With a pan suitable of containing gasoline, loosen the fuel bowl nut and catch the gas. Now remove the bowl nut and the bowl. Blow out the holes in the nut with compressed air or carburetor cleaner. Some Tecumseh carburetors have a tall bowl nut. Some will have a pin hole in the side of the nut, and some will have a pin hole just above the bottom set of threads. This hole must be clear in order for the engine to run properly.

    # For engines that do not have the jet made in the bowl nut (Kohler, Kawasaki, Honda, some Briggs and Strattons, Onan, Wisconsin-Robin) the jet is attached to the center post of the carburetor. Some are cast in and others are screwed in. Blow this hole out and blow up the center post to clean the main nozzle. Use compressed air or carburetor cleaner.

    # For all down draft Briggs and Stratton Flo-Jet carburetors (7, 8, 10, 11 HP Horizontal), remove the bowl nut (has adjusting needle in it) and blow compressed air up the nozzle. For Opposed Twin engines, Horizontal and Vertical, remove the bowl drain nut and blow air in that hole.

    2. Leaking Intake Gasket. Check for a loose carburetor or mainfold connection at the block. All Briggs and Stratton engine 3 to 6.5 HP, check the intake manifold for cracking (may have to remove carburetor) or loose connection at the block. You will need to remove the air shroud to get access to the intake manifold.

    source www.small-engines.com
    hell yeah lol
     
  4. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,022

    Good post but,

    What Mac explained is a non working governor. No mention of surging/hunting....:confused:
     
  5. MacGyver2

    MacGyver2 LawnSite Member
    Posts: 2

    What I observed when I first started it was semi normal operation. After a very short time I could see the governor control arm start bouncing backwards until it just rattled back fully to the rear and ran at max RPM. The arm was tight to the rod, too

    So you guys are telling me I have to crack this thing open (crack meaning disassemble the engine) and replace the whole governor gear, shaft, etc.
     
  6. topsites

    topsites LawnSite Fanatic
    Posts: 21,653

    Well now hold on, I'm sorry I got excited about that resource I found.

    But if that is the problem what I would do first is clean up all the linkages real good with carb cleaner and compressed air, maybe even a soft tooth brush, and then see about replacing that stupid spring and just make sure it's all like it's supposed to be, for all we know it's just worn or the stuff's dirty or both. Yes I know the carb's good, who put it in? That and there are other connections, I'd check all that out first, at least clean it all up real good and inspect for proper function.

    Now if that don't fix it, idk...
     

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