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My CB450 will not start no matter what.

Thread: My CB450 will not start no matter what.

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  1. ckemps's Avatar

    ckemps said:
    Quote Originally Posted by ancientdad View Post
    You mentioned "The cam and crank have been timed together correctly after rebuilding my cylinder head" and "I've pulled off the cam head cover" - are we talking about a DOHC CB450, or the later SOHC CB450? big difference in ignition and cam timing between the two

    I ask because when we don't have an Introduction, it takes longer for us to fully understand the new member and what bike he has...
    1974 Honda CB450 DOHC
     
  2. ancientdad's Avatar

    ancientdad said:
    Quote Originally Posted by ckemps View Post
    ...then a screw fell into the left cylinder and i got the cylinders bored and valves lapped and put everything back together but then it only ran on one cylinder (low compression) but would start (fall of 2018)
    So if I'm interpreting this correctly, the last time it ran it was the fall of '18 after the rebuild, but it only ran on one cylinder due to low compression... sounds like the top end condition would be the focus at this point, getting it started on one cylinder is pretty much unproductive
    Tom

    Ride along at the drag strip - https://www.youtube.com/watch?v=20jFPazXlvU



    running points... because I'm too old for mysteries that begin with pushing
     
  3. 76TWIN's Avatar

    76TWIN said:
    Wait... What?
    Did the screw fall into the cylinder while it was running?
    Why did you bore out the cylinders? Typically only a slight hone would be needed as boring usually mean you're going larger in piston and ring sizes.

    Even with lower compression, it should still fire if fuel and sparks are available and especially with the starting fluid.
    I'm thinking your ignition timing is way off somehow.
    '76 CB500T Frankenbike
    '73 CL450 (basket case for now)


    Carpe narem.
     
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  5. ckemps's Avatar

    ckemps said:
    Quote Originally Posted by 76TWIN View Post
    Wait... What?
    Did the screw fall into the cylinder while it was running?
    Why did you bore out the cylinders? Typically only a slight hone would be needed as boring usually mean you're going larger in piston and ring sizes.

    Even with lower compression, it should still fire if fuel and sparks are available and especially with the starting fluid.
    I'm thinking your ignition timing is way off somehow.
    in June of 18 a screw from the carb butterfly dropped into the left cylinder and welded itself to the piston (while it was running of course) and scratched the sh*t out of the cylinder wall. Cylinders were bored and piston sizes were extended from rings, so compression isn’t an issue. I agree the only possible explanation is still timing.
     
  6. ancientdad's Avatar

    ancientdad said:
    Quote Originally Posted by ckemps View Post
    ...and i got the cylinders bored and valves lapped and put everything back together but then it only ran on one cylinder (low compression) but would start (fall of 2018).
    Okay - so this above makes the most recent statement "Cylinders were bored and piston sizes were extended from rings, so compression isn’t an issue" confusing. Just trying to get a clear picture
    Tom

    Ride along at the drag strip - https://www.youtube.com/watch?v=20jFPazXlvU



    running points... because I'm too old for mysteries that begin with pushing
     
  7. mike in idaho's Avatar

    mike in idaho said:
    Since you've run a bunch of raw gas and starting fluid through it, trying to start it, it might be time to try a fresh dry set of NEW spark plugs.
    '65 YG1
    '65 CB160
    '66 CL160
    '67 CL77
    '68 TR6
    '69 T100R
    '69 T120R
    '72 Commando 750
    '78 XS650E
    '79 Gl1000
    '81 440 LTD
    My company car is a Kenworth
     
  8. 66Sprint's Avatar

    66Sprint said:
    Are you running stock pistons with over-sized rings, or did you replace both pistons and rings with oversize parts?

    BTW, both intake and exhaust valves are closed for the compression stroke and most of the power stroke....
    Intake valve closure (Just closing) indicates the compression stroke has started/is starting...
    Last edited by 66Sprint; 06-12-2019 at 01:14 PM.
    "I have a mind like a steel trap.....Old and rusty, of antiquated design, and hard to get stuff back out of...."
    Contact info: E-mail; [email protected] Phone; 540-525-5199
     
  9. ckemps's Avatar

    ckemps said:
    Quote Originally Posted by 66Sprint View Post
    Are you running stock pistons with over-sized rings, or did you replace both pistons and rings with oversize parts?

    BTW, both intake and exhaust valves are closed for the compression stroke and most of the power stroke....
    Intake valve closure (Just closing) indicates the compression stroke has started/is starting...
    Oversized pistons and rings.
     
  10. 76TWIN's Avatar

    76TWIN said:
    And you've checked the ignition timing? Set to fire on LF and F?
    '76 CB500T Frankenbike
    '73 CL450 (basket case for now)


    Carpe narem.
     
  11. ckemps's Avatar

    ckemps said:
    Quote Originally Posted by 76TWIN View Post
    And you've checked the ignition timing? Set to fire on LF and F?
    Yes, I've got solid spark at LF and F on compression for both cylinders respectively.