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  1. #1

    Default 2000 NS3.5B 2 stroke low compression

    This motor was originally purchased by my parents in 2000, they used it for 2 years before it sat in storage for a long time. I took it out recently and tried to fire it up with some fresh 50:1 mix, but it wouldn't start. Compression test showed low compression, about 40-50 PSI. Took the powerhead apart, found the piston ring was stuck in the groove, broke it trying to take it out and replaced it with a new OEM one (made sure it could move freely). Piston itself and cylinder walls looked to be in good condition, as well as the intake reed valve, so I did not replace those. Replaced the crankshaft oil seals, cylinder head gasket, drive shaft housing gasket and spark plug. After all this, I still only get around 50 psi, and when I spin the flywheel with a drill the motor almost wants to fire when I have the carb 3/4 full choke. Seems like somewhere compression is leaking but I'm stumped. I bought a cylinder leak down testing tool, and when the piston is TDC it holds pressure. Any help or suggestions on where to look next would be appreciated. At this point I'm wondering if the cylinder walls are out of spec or I need a new piston (isn't just the piston ring doing the real sealing work against the walls using a film of oil)?

  2. #2
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    3,053

    Default Re: 2000 NS3.5B 2 stroke low compression

    Should fire up, even at 50 psi. Then run to seat the new rings.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

  3. #3
    Join Date
    Jun 2013
    Location
    Duluth Mn
    Posts
    3,521

    Default Re: 2000 NS3.5B 2 stroke low compression

    Does spark jump 7/16" with a nice blue/white crackle? I'm sure you tried to prime it? Yes, as Paul said....it should start at 50 psi. Once fired up, you may need to clean carb...depending on how it was stored.

  4. #4
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    3,053

    Default Re: 2000 NS3.5B 2 stroke low compression

    Yep. Odds are the carb is funky.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

  5. #5

    Default Re: 2000 NS3.5B 2 stroke low compression

    Tried again today and cranked up to 75 psi!! Was able to get the engine to turn over, although she still seems to like a richer mix right now. Running with 25-30:1 mix for break in at low rpm. One other issue currently is, I broke a head bolt when attempting to replace the head gasket, and then broke a high speed steel drill bit trying to drill out the broken bolt. I currently have only 3 head bolts installed, and I see a little weeping from the head gasket area. Seems like I'll need to find a machine shop or someone to extract that drill bit and install all 4 head bolts.

  6. #6

    Default Re: 2000 NS3.5B 2 stroke low compression

    Managed to punch out the broken drill bit and tap new threads, all 4 head bolts installed and torqued to spec. No more weeping from head gasket! Thanks Paul and Tim for helping to troubleshoot and resurrect this motor. Can't wait to try it out on the river once the weather warms up!

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    Last edited by hungyzerglin; 12-02-2020 at 10:29 PM.

  7. #7

    Default Re: 2000 NS3.5B 2 stroke low compression

    One last question, I broke the #4 gasket sealing powerhead to driveshaft housing during disassembly and resealed the two surfaces uses high temp permatex red silicone RTV, which seems to be holding fine. However, the instructions say not to use silicone RTV where gasoline can contact. That area has water passages and the exhaust passage, will the seal eventually fail from exposure to unburnt gas vapors in the two stroke exhaust? Is it ok to use RTV?


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  8. #8
    Join Date
    Mar 2010
    Location
    Hamburg, NY, USA
    Posts
    3,053

    Default Re: 2000 NS3.5B 2 stroke low compression

    I would probably install a new gasket.
    Paul
    Certified Tohatsu TLDI Technician
    Hamburg, NY USA

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