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WEIRD surging 31P677

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Chilliman
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2020/02/27 21:37:27 (permalink)
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WEIRD surging 31P677

G'day all,
New today, live about 80kms south of Darwin, and my wife and I have a small engine repair business here for 8 years.
I have specialized in engine work since 1976 and in small engines since 2005.
The John Deere I have here, has a 31P677 0014 B3 motor.
It came here last week after she paid a local bloke $600 to overhaul the carby. (OOOFFFFFFFFF!!!!!!)
Her dad bought it here after the problem was not solved.
Checked the carby and the O ring for the fuel inlet was squashed replaced that and had a fairly healthy surge at all revs.
Checked inlet manifold for leaking gaskets and cracks and no warpage either end of the manifold, throttle spindle is good, jets correct.
There are no leaks at the fuel pump or the pulse tube to the sump. Filler tube O ring in good condition.
Ignition coli good ( checked on an Imrie 3000 I am proud to own)
When the motor ran I could hear a slight puffing noise, the compression was a little low.
I had been spraying a little carby cleaner near the engine end of the inlet motor and some of it blew back along the join between the cylinder head and the block and the revs flared up.
Replaced the head gasket.
Still the same surge.
Then it gets weird.
I sprayed some carby cleaner along the front edge of the sump gasket and the revs flared up dramatically.
WTF?
Took the motor out and replaced the sump gasket..................same.
Took the motor out and fitted a new gasket with Yammy bond............same
Took the motor out and just used Yammy bond................same.
If I spray carby cleaner underneath in the area of the screw that holds the heat shield.................revs climb also.
Could it be a porous cylinder?
If so how does the spray get past the liner in the cylinder.
When the spray is used the engine revs climb right away, but why do the engine revs climb when I am spraying CC at the sump gasket?
Maybe I'm not seeing the forest for the trees.
I NEVER say I have tried everything...............obviously I haven't.
Any ideas you blokes?
Thanks for having me here.
 
 
 
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    AVB
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    Re: WEIRD surging 31P677 2020/02/28 07:40:25 (permalink)
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    Double check your model and type number as I don't that one listed at at Briggs.
     
    This where you fall back to 2 cycle tests. Do a leak down test or pressure/vac test to find the leak. With the cylinder and crankcase pressurized use soapy water spray around area of suspected leak to locate exactly where the leak is. Takes the guessing out.
     
    If it turn out to be the cylinder head it may be warped. Note the current torque spec is 250 in/lbs. Using three steps, and follow the head torque sequence (pattern).
     
    Using 31P677-0144-B3 and your comments it sounds like you got a Nikki carburetor. You need to if you haven't check the main jet o-ring provided the jet haven't already got lost for a loose fit. a common problem area.
     
    I also assuming you did try doing the static governor adjustment if not then do one as someone else has already messed with the engine.
     
    BTW the Nikki is a fairly good carburetor but the fuel gasket set can be a pain if nicked or smashed. I had a batch of them to be bad from the distributor.
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    AVB
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    Re: WEIRD surging 31P677 2020/02/28 07:47:04 (permalink)
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    Also that 600 aud seem to be excessive. All it takes for a Nikki is a good ultrasonic cleaning and a set of bowl gaskets on most of the carburetors. and maybe a main jet(s) and a needle valve. I do enough of them that I keep five sets of gaskets in stock here.
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    Chilliman
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    Re: WEIRD surging 31P677 2020/03/18 02:17:19 (permalink)
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    G'day you blokes,
     
    Well I have continued with trying all suggestions with no success.
     
    After all (not all because I haven't figured the problem it is still exactly the same) attempts and clutching at straws, I sprayed the block with a ceramic engine paint in the hope any porosity might be sealed.
    Three solid coats, that were left to set in 4 days of outback sun eg. 38-40C, we refitted the motor with a brand new carb, and still exactly the same.
    Is anyone interested in seeing a video of this, of when the motor surges, but when carby cleaner is sprayed under the block the motor runs smooth as....?
    ALSO.............apparently this problem has existed since the mower was purchased some years ago and the dealers
    just kept finding some other reason for the motor misbehaving, then when warranty had run out, told them to "go away".
    ALSO the ID is definitely 31P677 0144 B3.
     
     
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