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Thread: TB42 won’t start

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    TB42 won’t start

    Hi, Im hoping someone can spot the obvious reason that I have missed trying to get my ’89 TB42 manual SWB to start.

    For a while she has backfired on occasion when you came off the pedal and she idled a little rough at times but fuel economy was good as was power. She is fitted with a Petronix ignitor.

    Of late the backfire got worse and she started to miss so I decided to give the whole system a good overhaul. I did this in stages as parts arrived but she gradually got worse until she now simply won’t start.

    She turns over on the starter.
    I have replaced the coil with a flamethrower, removed the resistor, replaced the dissy cap and rotor (not an extended version), replaced the plugs and leads, put in a new mechanical fuel pump and filter, and put an overhaul kit through the carb.

    I have confirmed that I am getting spark at all six plugs, have tried powering the Petronix direct from the battery and checked the voltage at the coil so I am pretty sure it is not electrical.
    I have confirmed that fuel is getting to the carby and can see fuel being delivered into the carby when the accelerator is depressed.
    I have tested compression (cold obviously) which is good and consistent across the cylinders.
    I have checked all the vacuum pipes and made up new ones where needed.
    I have cleaned the EGR value which rattles correctly.
    The needle and float seemed good when I put the kit through the carby and I have tried another carby from an auto which has been sitting around for years.

    But still nothing; she cranks but refuses to start and eventually spits fuel back out through the top of the carby. I am now at a bit of a loss what to try next. Any suggestions would be much appreciated.

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  3. #2
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    G’day LW Mate!
    Probably no help here as I too became frustrated with petrol donks years ago.
    Flashing back, you say mate that you’ve got “spark” (bright blue/white or pale orange) it can matter IIRC?
    Your written description so far to my nuffy mechanical understanding still sounds like a fuel issue?
    Try cutting off the fuel completely and squirt some ‘start U bastard’ and or CRC/WD40 down its throat to see quickly if it will at the least kick a rotation or two to isolate spark/fuel ?


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    Patrol God mudnut's Avatar
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    Plenty of things to check.
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    MB (29th July 2020)

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    Fair call Muddy Mate
    Maybe a flooding choke situation??


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    Patrol God mudnut's Avatar
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    I reckon it was a timing issue at first, but too much fuel will cause a back fire and flooding.

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    If it were nuffy me, I’d start with zero fuel going in and a can of explosive shit squirting in hand to isolate one of two issues :-)


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    Timing,if you have spark,you have fuel and you have compression.....it has to be timing
    If that's out it's got everything but not at the right time,try and get top dead centre...take a plug out turn motor over by hand and feel the piston in number 1when it is at the top....yiu should feel it....check timing marks

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    Who twisted his sister though, not mentioned?


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    Thanks guys. I checked the timing when I first replaced all the electrical components (and still running sort of) and it was good so I am struggling to see how that might be the issue, which leaves the fuel option. I will go try MB's idea.....

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