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  1. #1
    Join Date
    Apr 2011
    Location
    Me: Midlands, Boats: East Coast
    Posts
    370

    Default Two-stroke conundrum

    I have gone through all the bits I can think of and now could do with some pointers.
    Engine is a Mariner 5hp 2-stroke, made in Belgium. Internal and external fuel tank. It was running fine a couple of weeks ago but had a fuel leak so I brought it home. The leak is now cured but now it refuses to start.
    So far I have:
    Drained everything and put in fresh petrol from the local garage (the TCW3 oil is a couple of years old though).
    Cleaned the pipes, filter, one-way valve and fuel pump.
    Disassembled the carb fully, sprayed it with carb cleaner, blown through with air at 8bar and reassembled.
    Checked for a good spark and gapped the plug anyway. It looks new though
    The reed is not stuck.
    There is compression.
    Tried every combination of choke and throttle and not even a fart out of it.

    Fuel is getting into the cylinder and wets the plug when using the choke.
    It fires briefly if carb cleaner is sprayed in. Masses of heavy white smoke!
    I removed the recoil starter and used a battery drill with socket to flywheel nut to spin the engine at speed.and it does not start but a slight haze of smoke is produced from the exhaust.
    When it ran before it seemed noisier than my Seagull Featherweight, which surprised me!

    I am now stumped. Any suggestions as to what it might be?
    De'il ding a divot auf yer wame wi a flaughter spade

  2. #2
    Join Date
    Aug 2009
    Location
    Belfast
    Posts
    1,477

    Default Re: Two-stroke conundrum

    Try a new plug.

  3. #3
    Join Date
    Nov 2009
    Location
    Home UK Midlands / Boat Croatia
    Posts
    20,428

    Default Re: Two-stroke conundrum

    I would definitely try a brand new spark plug just to rule that out.

    Richard

  4. #4
    Join Date
    May 2001
    Location
    North from the Nab about 10 miles
    Posts
    8,847

    Default Re: Two-stroke conundrum

    I would start with a new plug. 2T plugs can be very odd, particularly if it has been wetted with fuel.

    Other Possibles:

    1 Carb incorrectly assembled? Missed putting a part back in such as pilot jet or emulsifier tube? Needle incorrectly mounted. If the plug is wet its maybe getting too much fuel due to a missing carb bit?

    2. Spark timing slipped due to loose flywheel causing the key to shear? Unlikely, but I have had it happen. very difficult to spot what had gone wrong.
    Last edited by oldharry; 05-08-19 at 21:18.
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  5. #5
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,614

    Default Re: Two-stroke conundrum

    Quote Originally Posted by Rum Run View Post
    I have gone through all the bits I can think of and now could do with some pointers.
    Engine is a Mariner 5hp 2-stroke, made in Belgium. Internal and external fuel tank. It was running fine a couple of weeks ago but had a fuel leak so I brought it home. The leak is now cured but now it refuses to start.
    So far I have:
    Drained everything and put in fresh petrol from the local garage (the TCW3 oil is a couple of years old though).
    Cleaned the pipes, filter, one-way valve and fuel pump.
    Disassembled the carb fully, sprayed it with carb cleaner, blown through with air at 8bar and reassembled.
    Checked for a good spark and gapped the plug anyway. It looks new though
    The reed is not stuck.
    There is compression.
    Tried every combination of choke and throttle and not even a fart out of it.

    Fuel is getting into the cylinder and wets the plug when using the choke.
    It fires briefly if carb cleaner is sprayed in. Masses of heavy white smoke!
    I removed the recoil starter and used a battery drill with socket to flywheel nut to spin the engine at speed.and it does not start but a slight haze of smoke is produced from the exhaust.
    When it ran before it seemed noisier than my Seagull Featherweight, which surprised me!

    I am now stumped. Any suggestions as to what it might be?
    How good is the spark ? "good" is not good enough It should jump about 7/16"

    Try a new plug

    What is the compression "there is compression" is not accurate enough. It might run at 60psi . it should run at 80 it should run well at 100. but if over 120 your gauge is probably wrong.

    Cannot tell from here if you have reassembled the carb and fuel pump correctly or if your cleaning procedures have been effective. I like to poke a soft copper wire ( eg fuse wire) through the jets.

    Have you checked the float height . Later models, and earlier models fitted with a replacement soft tip needle should have a little clip between the needle and the float arm.

    Id check the flywheel key. It may have sheared and allowed the flywheel to move on the shaft especially if the flywheel has ever been removed and the retaining nut not torqued to the correct figure on re-assembly.

    I once had trouble with some old 2 stroke oil. Initially it fouled the carb but the dregs in the bottle eventually went all "gloopy" and would not mix with the fuel.
    Last edited by VicS; 05-08-19 at 21:46.

  6. #6
    Join Date
    Sep 2001
    Location
    Me - Zumerzet Boat - Wareham
    Posts
    12,295

    Default Re: Two-stroke conundrum

    Electronic ignition or points?
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  7. #7
    Join Date
    Apr 2011
    Location
    Me: Midlands, Boats: East Coast
    Posts
    370

    Default Re: Two-stroke conundrum

    I will try a new plug. Cheap to eliminate anyway

    I believe the carb is correctly assembled but there was crud in the pipes, filter and pump so maybe I missed something in the carb. I would have expected some sign of ignition though, even if just a short burst before it flooded / starved. It reliably fires on carb cleaner!

    Flywheel seems tight but I have had a sheared key on another Mariner so will check. This engine has electronic ignition so cannot check the points against TDC
    De'il ding a divot auf yer wame wi a flaughter spade

  8. #8
    stingo is offline Account Closed (By user's request)
    Join Date
    Oct 2001
    Location
    Algarve
    Posts
    9,394

    Default Re: Two-stroke conundrum

    If it reliably fires on carb cleaner, that suggests the fuel mix getting to the sparkplug is wrong, which suggests your primary jet is not perfectly clean. Poke as thin a piece of wire as you can get your hands on through it, but don't force the wire in.

  9. #9
    Join Date
    May 2018
    Posts
    745

    Default Re: Two-stroke conundrum

    Clean up the plug and squirt/drip or otherwise introduce a few drops of raw fuel down the plug'ole. Replace plug.
    See if it runs for a few seconds. If it does it's carburation. If it doesn't it's probably ignition.

  10. #10
    Join Date
    Apr 2011
    Location
    Me: Midlands, Boats: East Coast
    Posts
    370

    Default Re: Two-stroke conundrum

    Quote Originally Posted by VicS View Post
    How good is the spark ? "good" is not good enough It should jump about 7/16"
    definitely 10mm but will check again
    Try a new plug

    What is the compression "there is compression" is not accurate enough. It might run at 60psi . it should run at 80 it should run well at 100. but if over 120 your gauge is probably wrong. Not got a gauge, just feeling it when turning flywheel by hand. Worth getting one though I suppose

    Cannot tell from here if you have reassembled the carb and fuel pump correctly or if your cleaning procedures have been effective. I like to poke a soft copper wire ( eg fuse wire) through the jets. Good light and close up glasses showed no dirt in the jets, but not sure about all the galleries. If other things don't work I'll have it to bits again and it can go in the ultrasound tank

    Have you checked the float height . Later models, and earlier models fitted with a replacement soft tip needle should have a little clip between the needle and the float arm. There is a clip, haven't checked the float height though

    Id check the flywheel key. It may have sheared and allowed the flywheel to move on the shaft especially if the flywheel has ever been removed and the retaining nut not torqued to the correct figure on re-assembly. Will check

    I once had trouble with some old 2 stroke oil. Initially it fouled the carb but the dregs in the bottle eventually went all "gloopy" and would not mix with the fuel. It dispersed nicely in the fuel but worth considering
    Thanks Vic
    De'il ding a divot auf yer wame wi a flaughter spade

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