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bike wont start

Discussion in 'Using this forum - Help and Feedback' started by lilemma, Aug 6, 2014.

  1. lilemma

    lilemma Member

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    I have a 1983 sportster was ridding it around it was running fine I stopped at a stop light when I took off again the bike just back fired and died now it won't start it cranks then back fires really hard I took heads to shop and they ground down exhaust valves and did something with intake valves to I put new plugs in it as well and still doing the same thing please give me some advice on what could be causing this thanks
  2. hotroadking

    hotroadking Super Moderator Staff Member

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    are you saying you took the heads off AFTER the problem to have the work done
    or that was the work done prior to the problem of the backfire and no start.
  3. lilemma

    lilemma Member

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    The work was done after the problem someone said to check the heads and make sure they werent blown and we saw that the exhaust valves were a little beat up so I took the heads in to get them worked on but its still doing the same
  4. hotroadking

    hotroadking Super Moderator Staff Member

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    So that pretty much rules the heads out as the cause,

    You need three things to get an engine to run

    1) fuel
    2) spark
    3) Compression

    Test the compression on the cylinders, you can get an inexpensive tester at any auto parts store, you are not building NASCAR engines so you don't need one from Snap On. Be sure you are getting good compression on both cylinders.

    Next, fuel, are you getting fuel, check the carb, float, take off the filter and twist the throttle, is it squirting fuel into the carb

    Finally Spark, are you getting spark at the plugs,

    my guess would be short of some internal problems
    that you have a bad coil, or ignition module sounds like timing is off.
  5. lilemma

    lilemma Member

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    Ok I'll try that thank you
  6. lilemma

    lilemma Member

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    I did the compression test the back jug is at 135 psi the front is 120 not sure where it should be and why they are different
  7. hotroadking

    hotroadking Super Moderator Staff Member

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    That sounds low. Did you have the throttle open fully when you did test?
  8. lilemma

    lilemma Member

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  9. lilemma

    lilemma Member

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    Would it be a gasket or maybe timming how can u tell without taking to a shop cant afford that
  10. hotroadking

    hotroadking Super Moderator Staff Member

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    Air filter on or off... is the carb opening 100% with the filter off make sure it's going to full open do you have a cv carb, make sure the slide is coming up all the way, so you can get all the air in when checking.

    Just off the top of my head it sounds like it's got low compression figures
    I would think they would be closer 150 to 160 and no more than 5 to 7 lbs off from each other. But I don't know sporty comp numbers, maybe someone will chime in that has the specs.

    Low comp results from valves not closing tight or busted rings not sealing,
    gasket leak etc anything that won't let it build pressure.

    Does it have adjustable pushrods or did you put the stock rods back


    The timing isn't going to change compression,

    Have you checked fuel and spark yet.
  11. lilemma

    lilemma Member

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    I found a leak in one of the head gaskets bolts werent tight enough both jugs are reading 135 now but still won't start I checked for spark seem to be pretty good and pulled the fuel line it's coming out to the carb not sure how to check if its going threw the carb is there a way to check if rings are bad without spending a bunch of money at shoo
  12. hotroadking

    hotroadking Super Moderator Staff Member

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    Yes you do a leak down test, the only way to do it right is to remove the pushrods, this closes the valves otherwise you have to turn it over and be dead sure you are at TDC meaning the valves are closed completely.

    Remove the plugs from the engine

    With an air compressor fully charged and the trans in first gear with someone holding the rear brake and using an adapter on the air line that will allow you to put air into the cylinders, one at a time.

    When you pressurize the cylinder listen for leaks out of the intake or exhaust then you have a leaking valve, if you hear it going down into the crank case you have ring issues.

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