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Briggs and Stratton 19.5 hp 42e707 Hunts and Surges

I just bought a used craftsman rider ('98 19.5 hp 42" deck). When I got it, it wouldn't start at all. I've replaced the plugs (good spark), air filter, fuel filter, and changed the oil. I disassembled the carb, cleaned it out, reassembled. Then, it would fire on first attempt, run for about 5 seconds and then die out. After that, it would not fire on restarting attempts. I pulled the carb again checked passages, needles, ports, etc. Reinstalled and same thing...fires, runs for a few seconds, and then dies.

So today, I had a buddy check it out, we took everything apart again, inspected all the jets, ports, etc, reassebled and it ran. Now the problem is that it hunts and surges and also back fires from time to time. Adjusting the throttle has minimal effect on the hunting and surging however at higher throttle setting, the backfires seem to be more often. I don't have a manual on the engine (and it seems impossible to find any documentation online) so I don't know what, if any, screws can be adjusted in the governor linkage chain to settle the governor down.

Any suggestions??


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  • gdrum3581 Sep 10, 2009

    Sorry, yes I believe I have good flow. Initially, when it was dying and not restarting, I think it was flooding (not positive on that). Nonetheless, there is fuel flowing through the clear fuel filter and the bowl does have fuel in it, even ater running for a while.

  • gdrum3581 Sep 10, 2009

    I shot carb cleaner through all the passageways I could find. When I first disassembled, it seemed pretty clean. I didn't really notice any buildup, blockages, etc. I can't even say I noticed any shellac.

    As for fuel flow, it seemed to be flowing freely. I don't know of a way to quantify too much vs not enough. Please advise.

    I also just installed a new fuel filter and its clear so I do see the fuel in it and do not observe any debris in it.

    The fuel pump is vaccuum operated, or at least I think. It mounts directly to the front of the carb. It is a two chamber plastic body with a fuel supply line coming in, and what I'm assuming to be a vaccuum tube that goes out to the block.

  • gdrum3581 Sep 11, 2009

    Wow, lots of good points to check. I won't get to follow up on these until next week but will definitely do so. To answer some of your questions: Yes I disassembled the fuel pump and it seemed ok. The diaphram was flexible and pliable, with no holes or cracks. One thing to note is that I have not replaced and gaskets or diaphrams as I was figuring that I would at least get it running before I installed new gaskets and diaphrams. I didn't want to put new stuff on and then damage it while taking it on and off multiple times. So, I think I will order new stuff now that it is running and see if that helps the air/fuel mixture. Seem reasonable?
    Oh, and I don't really know the history of the engine before I bought it. I believe the previous owner said it ran earlier this summer and then just stopped. He was under the belief that his wife put race gas in the tank while he was on travel. He said he tried starting it and just gave up and used his other mower.

  • Wayne Holden May 11, 2010

    Do you have good fuel flow into the carb?



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Are you sure you got all the passageways in the carb cleaned out?

How did it look when you first disassebled it? Full of rust and gunk or just shellac on the surfaces?

Take the fuel line off at the carb and MAKE SURE that fuel flows freely. I have seen trash get in the tank and plub the other end up. Does it have a vaccuum operated fuel pump?

Posted on Sep 10, 2009

  • Wayne Holden Sep 10, 2009

    Ok, so we have clean fuel getting to the pump.

    Did you disassemble the pump? Is the diaphram still flexible? Any cracks?

    Too much fuel would flood the carb and would actually be caused by a leaky float valve, you would have fuel dripping till the bowl was below the overflow point and it would be hard to start and blow black smoke once it did start.

    Too little or poor fuel control and it will do what it is doing already, of course this isn't the only thing that can cause the symptoms, just the most likely.

    The air filter is new and all electrical connections are secure so that leaves us with fuel/air mixture.

    Double check all your work, anywhere you took something off or apart and make sure it is back in it's correct position, any air leak will play hell with the mixture and these engines are picky, just not a lot of play room. Was the intake gasket good or did you replace it?

    Another consideration that I saw once on a Honda engine, loose intake valve keeper. Actually ran that way, just not very well, backfired, surged, hard to start. Consider a leaky valve or one that is poorly seating.

    How long since this engine was in use before you got it?

  • Wayne Holden Sep 11, 2009

    Race gas? As in high octane or worse? Check your compression. If it is low, that will also mean a decrese in vaccuum which runs the fuel cycle, the whole cycle not just the fuel pump. High temp from the wrong fuel could have caused the rings to loose their tension, end result, lost compression/power.

    Good luck.


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Try cleaning the flywheel and the coil and reset the air gap about .009 (thousanths) i just got a 19.5 b&s sometime it would start after it got warmed up wait until next day then it wwould start . hope this will help you . the old man

Posted on Oct 19, 2011


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