Briggs & Stratton 12.5 HP(ID# 288707) timing question

Discussion in 'Mechanic and Repair' started by lostinspace, Mar 10, 2006.

  1. lostinspace

    lostinspace LawnSite Member
    Posts: 2

    My brother inlaw replaced a rod in this engine (with no manual) and after assembly, he says he can only get it to backfire with the choke out. I was wondering if he could have got the camshaft/crankshaft timing wrong? He said he ligned up the marks. Is it that simple?
    This engine (1995) has electronic ignition, so there is no points, correct?
    Is there some other timing I should be concerned with?
    I was just going to make sure the gas is good and the plug is gapped a .30.
    I also noticed a post here
    "Its possible there was some trash in the float bowl thus when you flipped the engine around working on it some got in the main jet,I have had this happen.Clean the carb. out and see what happens,If this doesn't do it explain in better detail what its doing."
    I will do this as well.
    Hope someone can answer my questions:
    Cam/crank timing?
    No points to worry about?
    Any additional timing to be concerned with?
    Any other troublshooting tips?

    Thanks much for any help.
     
  2. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    (1) Cam timing is aligning the dot on the crank gear with the dot on the cam gear.

    (2) No points, It has electronic ignition. Make sure the coil to flywheel air gap is 0.10" to 0.12" gap, The use of any business card will do most are 0.10".

    (3) Check the flywheel key.

    Clean the carb. as you said and let us know what happens.
     
  3. lostinspace

    lostinspace LawnSite Member
    Posts: 2

    1) Cam timing is aligning the dot on the crank gear with the dot on the cam gear.

    (2) No points, It has electronic ignition. Make sure the coil to flywheel air gap is 0.10" to 0.12" gap, The use of any business card will do most are 0.10".

    (3) Check the flywheel key.

    Clean the carb. as you said and let us know what happens.

    We tried all the above and the engine still backfires out of the carb when trying to start (with choke on), otherwise, it just cranks over with no indication of starting.
    Pulled the head and all valves seem to be working correctly, both are closed at TDC and they are opening and closing fine.The plug seems to be firing really well.
    Took the carb apart but it seemed really clean BUT, very unfamiliar with these carbs but did seem like a whole lot to them.
    Really don't know what else to try.
    any additionaly help is greatly appreciated.

    Thanks.
     
  4. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    Post the type number off the engine, Is it a Walbro or Nikki carb. ? Was the coil removed from the engine when this job was done ? backfiring out the carb. sounds like a intake valve not seating well, Possibly a worn valve guide.
     
  5. C&K Trucking

    C&K Trucking LawnSite Member
    from WV
    Posts: 7

    Also check the gap is correct on the spark plug , I have seen the wrong gap setting do some crazy thing's to these engines.
     
  6. remaxey

    remaxey LawnSite Member
    Posts: 2

    Lostinspace: I am curious as to what you found the problem to be ? I just replaced the connecting rod on a 17.5 hp single cylinder 31C707 type 0154 and it is doing the same thing you described, yet I cannot find my problem. If you could let me know what you did to correct I would very grateful. Thanks
     
  7. Phil G

    Phil G LawnSite Senior Member
    Posts: 843

    Have you checked the gap with feeler gauges when the valves are closed? Don't check on tdc. One fully opened then check other valve. This is not the factory way, but will confirm they are fully closed and gapped.

    Or, maybe as you suggested the cam/gear timing is out d'oh
    Good luck Phil :)
     
  8. sawman65

    sawman65 LawnSite Senior Member
    Posts: 751

    good job phil, took the words out of my mouth lol!
     
  9. Phil G

    Phil G LawnSite Senior Member
    Posts: 843



    Great minds think alike :D:clapping:


    Let's hope we got it right
     
  10. kawasaki1

    kawasaki1 LawnSite Member
    Posts: 108

    see if the coil is mounted upside down.
     

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