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Featured 1975 Sear SS16 - sparks out exhaust

Discussion in 'Craftsman / Sears' started by mdroll7780, Sep 27, 2017.

  1. mdroll7780

    mdroll7780 New Member

    Apr 26, 2017
    Hey everyone-

    I bought a 1975 Sears Auburban SS16 back in March, and been working out the bugs ever since. You guys have helped me on a few things and thought I was good to go, until last week. Here the symptoms:

    1) It seems to have been harder to start lately. Cranks strong but doesn't seem to fire. A spray of starter fluid in the carb gets it started up and running. This isn't all the time, but often. This may be a separate issue, but my first thought was the fuel pump wasn't working well, and maybe starts to work better once its running. Just wanted to mention this.
    2) Once running, and give 45-60 seconds to warm up a bit, I can go on running no problem. After about 10 minutes, running with the mower deck engaged, it sputters and stops. I also noticed some sparks flying out the exhaust as shee was sputtering and quitting. Im not sure what would cause this, as it looked like sparks, not backfire flame type.
    3) Once she quits, it does not like to start right away, but give 15-20 minutes to cool off it seems to start up again, but will have the same issue 10 minutes later.
    4) While running WOT and mowing, there seems to be a lot of heat coming back at me from the motor. I seem to remember my Dad's 1978 SS18 always having a lot of hot air so figured maybe these Onans just run kinda hot. Not sure but wanted to mention.

    Oil levels checked and OK. Im concerned the sparks are being created by hot metel to metal contact inside the engine and spitting them out exhaust? I don't know, but worried about damaging the motor. Any insight, or things to check is much appreciated.

    Here is sears model and Onan numbers:

    Sears model is 917.25884
    Sears Serial 8155

    Onan model: BF-MS/2833D
    Onan serial : D753110349


    Attached Files:

  2. Bill Kapaun

    Bill Kapaun Member

    May 8, 2007
    Sparks are probably burnt carbon.

    Clean the debris from under the cooling shroud.
    Replace fuel filter.
    jhngardner367 likes this.

  3. mdroll7780

    mdroll7780 New Member

    Apr 26, 2017
    I replaced fuel filter, and checked all the cooling shrouds. There was no debris stuck in the shroud. Quite clean actually. I used it this past weekend and it ran for about 25 minutes, maybe 30, and thought I was in the clear, but then did the same things as originally described.

    Would the diaphragm fuel pump be a possible suspect? Sometimes I wonder if its drawing strong enough, as I noticed the fuel filter looks like not much fuel inside it when running. Should the filter be completely full of fuel while running? I don't know if this might cause these symptoms if so?

    I am perplexed at the timing of when it happens. Possibly an ignition coil that acts funny when it gets hot? More pondering I suppose. Let me know of any other thoughts, and as always appreciate your guys input.


  4. Searsnutt

    Searsnutt New Member

    Nov 17, 2013
  5. Searsnutt

    Searsnutt New Member

    Nov 17, 2013
    Start by replacing the diaphragm fuel pump with an electric one. May not solve all your problems, but solved the fuel delivery issue I encountered with my tractor. About $12-15 on ebay. Search for:Universal Car - Boat - Generator 12V Low Pressure Fuel Pump Diesel Gas Fuel Oil
  6. Bill Kapaun

    Bill Kapaun Member

    May 8, 2007
    Check the quality of spark when cold and again when the problem occurs.
    Compare before/after.

    Likely the coil is heat sensitive, thus my recommendation about cleaning under the shroud.
  7. Larry/car

    Larry/car New Member

    Sep 1, 2017
    Replace points and condenser, possibly coil gets hot and electrical circuit opens.
  8. jhngardner367

    jhngardner367 Moderator Staff Member

    Apr 4, 2011
    When it shuts down, IMMEDIATELY put a spark tester on it,and see how the spark looks.
    If it looks good(blue),then the trouble could be :
    A) A blown head gasket.
    B) A bad valve.
    C)fuel pump ,or carb problem.
    D) Carbon built up on a piston,or valves.
  9. belchermw

    belchermw Supporting Member Supporting Member

    Apr 4, 2017
    Burned exhaust valve

    Sent from my iPhone using Tractor Forum
  10. Arkie

    Arkie New Member

    Aug 6, 2014
    Onan engine.

    Parts kinda costly.

    I would get a old spark plug ready and when she quits pull a plug wire, connect the spark plug and ground it good and take a look. Do this on both cylinders but always keep one plug wire connected to a plug. (they are in series for spark on those engines Called waste spark ignition system.
    One open plug wire weakens fire to the other plug.
    You also need to make sure some Bubba has not installed the wrong spark plugs. Pull a spark plug and tell us if the tip is sooty or clean.
    If you have good spark remove the gas line and the carb and put it in a catch can and crank the engine while it's hot and check for good fuel deliver. If weak fuel delivery from a pulse/vacuum type fuel pump place the input line in a little can of gas and see if it then pumps. If so your fuel line to the tank is bad, filter screen in tank restricted, or pump is sucking air.
    The sparks are mostly likely just carbon that is coming out as it hiccups.
    You need to determine if the issue is ignition or fuel.
    I had one doing that and it was both the ignition coil and the points. (If it's a bad coil be sure you get the correct one)

    I've got one of them old SS16's with a Briggs Twin and it just keeps going like the energizer Bunny. I have a little trailer behind it and use it almost daily around the place as a GO for (GOPHER) rig and it tows a wood splitter thru the woods where a larger tractor or vec won't go..
    Last edited: Oct 19, 2017