Would a blown power valve cause...
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Would a blown power valve cause...

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    Senior Member Delemorte's Avatar
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    Default Would a blown power valve cause...

    Detonation at low RPM? Last weekend i got my motor back in and on the water. Unfortunately for me i forgot i loosened the dissy hold down bolt so the dissy went way off and she back fired a few times...


    Got it sorted out but since then at low RPMs she started pinging.. Not real bad mind you but i have been warned detonation can be bad regardless... Thought maybe my idle or somethign was off but that aint it..


    When i bought the carb i was told that the carb was not modded to prevent damage to the power valve so im hoping i just toasted it. I got three more sitting here so if thats the case no biggy... just didnt know if a bad one could cause detonation.

    Seems to only be coming from the passenger side so once it cools down ill pull that cover off again.
    Quote Originally Posted by jetboatperformance View Post
    the ensueing fire would likely be extinguished by the sinking however

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    Senior Member gregb's Avatar
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    Doubtful, since it would be letting more fuel in once you were off the idle circuit and onto the mains. I have had plenty of backfires over the years and not one resulted in a blown valve, even in the carbs without the protection, only time I've had them go bad is from sitting. If the valve isn't opening it could cause a lean condition. Did you reset the timing with a light or just eyeball it?

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    Senior Member Delemorte's Avatar
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    Quote Originally Posted by gregb View Post
    Doubtful, since it would be letting more fuel in once you were off the idle circuit and onto the mains. I have had plenty of backfires over the years and not one resulted in a blown valve, even in the carbs without the protection, only time I've had them go bad is from sitting. If the valve isn't opening it could cause a lean condition. Did you reset the timing with a light or just eyeball it?

    light.. 15 initial.. 35 total at 3200..
    Quote Originally Posted by jetboatperformance View Post
    the ensueing fire would likely be extinguished by the sinking however

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    Senior Member Delemorte's Avatar
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    pulled that valve cover. those vlaves seemed a little tight. So much i might have been "floating" them. I hope that the correct word. Where they never fully close... would that hot exhuast set off fresh fuel/air if it leaked out to it? or am i dreamin..


    not the super mechanic here... :-)
    Quote Originally Posted by jetboatperformance View Post
    the ensueing fire would likely be extinguished by the sinking however

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    E-7 Sheepdog (ret) SmokinLowriderSS's Avatar
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    No, it will not cause detonation, it will cause severe over-rich at idle, and sligthly less, but still over-rich at above idle.

    The PV passses fuel thru a hole in the bottom of the carb, and passes fuel constantly if the diaphram is damaged/destroyed, whether the main circuit is in operation or not.
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    Sit N' Spin Jetaholic's Avatar
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    Quote Originally Posted by SmokinLowriderSS View Post
    No, it will not cause detonation, it will cause severe over-rich at idle, and sligthly less, but still over-rich at above idle.

    The PV passses fuel thru a hole in the bottom of the carb, and passes fuel constantly if the diaphram is damaged/destroyed, whether the main circuit is in operation or not.
    Under normal operation, the only thing that goes through the hole at the bottom of the carb is the manifold vacuum signal that operates the power valve. The fuel passes through the power valve, then through the PVCRs into the main wells.

    The pressure wave from an intake backfire reaches the mechanical assembly of the power valve through this hole and severely bottoms out the power valve diaphragm, which usually tears the diaphragm. Only then will fuel be able to constantly free flow straight into the manifold through the bottom of the carb. A worn power valve spring can also cause this (the spring is what opens the power valve when vacuum falls below a certain point, and seals off the vacuum side of the power valve from fuel flowing to the vacuum side when it is open).

    Delemorte, have you removed the dizzy cap and done a visual inspection of the mechanical advance? Wondering if you may have a broken spring, which would cause your advance curve to come in much too quick.
    Last edited by Jetaholic; 07-17-2009 at 03:53 PM.



    Quote Originally Posted by HammerDown
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    Well I am putting in a nice stereo system in the Carrera...maybe Ill put on some rap and turn the scoop sideways

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    Senior Member Delemorte's Avatar
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    Quote Originally Posted by Jetaholic View Post

    Delemorte, have you removed the dizzy cap and done a visual inspection of the mechanical advance? Wondering if you may have a broken spring, which would cause your advance curve to come in much too quick.

    I have not.. let me look...

    Checked.. Spring and bushing intact and rock solid.
    Last edited by Delemorte; 07-17-2009 at 04:10 PM.
    Quote Originally Posted by jetboatperformance View Post
    the ensueing fire would likely be extinguished by the sinking however

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    Sit N' Spin Jetaholic's Avatar
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    Quote Originally Posted by Delemorte View Post
    I have not.. let me look...

    Checked.. Spring and bushing intact and rock solid.
    OK...what RPM range is it detonating at? Also, are you running a solid or hydraulic cam?

    Also what do your plugs look like? Can you post some pics of them?
    Last edited by Jetaholic; 07-17-2009 at 04:27 PM.



    Quote Originally Posted by HammerDown
    Kendall L-427 Super Blu...extreme-pressure (ep) lithium complex keeps my thrusting balls happy
    Quote Originally Posted by back2k5 View Post
    Well I am putting in a nice stereo system in the Carrera...maybe Ill put on some rap and turn the scoop sideways

  11. #9
    Senior Member Delemorte's Avatar
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    Quote Originally Posted by Jetaholic View Post
    OK...what RPM range is it detonating at? Also, are you running a solid or hydraulic cam?

    Also what do your plugs look like? Can you post some pics of them?

    900 - 1000 RPMs at idle and stops above 1500... Im really thinking my exhuast valve was not closing all the way.. I re-adjusted the valves and will take it back out in the AM.


    Edit: Forgot.. Solid lifters. ive had sucha time with solid lifters i want to toss that shit and put in a hydrolic cam sometimes.
    Last edited by Delemorte; 07-17-2009 at 08:29 PM.
    Quote Originally Posted by jetboatperformance View Post
    the ensueing fire would likely be extinguished by the sinking however

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    Senior Member Delemorte's Avatar
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    adjusted those exhuast valves. Detonation resolved.. I think those exhuast valves just were not closing and air/fuel was making it to the exhaust pipes unburned.
    Quote Originally Posted by jetboatperformance View Post
    the ensueing fire would likely be extinguished by the sinking however

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    Sit N' Spin Jetaholic's Avatar
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    Quote Originally Posted by Delemorte View Post
    adjusted those exhuast valves. Detonation resolved.. I think those exhuast valves just were not closing and air/fuel was making it to the exhaust pipes unburned.
    If that were the case, I'd be more willing to bet that the sound you were hearing was the piston contacting the valve due to it being partially open.



    Quote Originally Posted by HammerDown
    Kendall L-427 Super Blu...extreme-pressure (ep) lithium complex keeps my thrusting balls happy
    Quote Originally Posted by back2k5 View Post
    Well I am putting in a nice stereo system in the Carrera...maybe Ill put on some rap and turn the scoop sideways

  14. #12
    Senior Member Delemorte's Avatar
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    Quote Originally Posted by Jetaholic View Post
    If that were the case, I'd be more willing to bet that the sound you were hearing was the piston contacting the valve due to it being partially open.

    Maybe but i dont think so... Sounded more like someone tapping my exhuast pipe.
    Quote Originally Posted by jetboatperformance View Post
    the ensueing fire would likely be extinguished by the sinking however

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    Default Adj method?

    Quote Originally Posted by Delemorte View Post
    900 - 1000 RPMs at idle and stops above 1500... Im really thinking my exhuast valve was not closing all the way.. I re-adjusted the valves and will take it back out in the AM.


    Edit: Forgot.. Solid lifters. ive had sucha time with solid lifters i want to toss that shit and put in a hydrolic cam sometimes.
    Which method of adjustment do you use, just asking..........Ray
    LOUD BOATS SAVE LIVES

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    Senior Member Delemorte's Avatar
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    [QUOTE=Moneypit;752508]Which method of adjustment do you use, just asking..........Ray[/QUOTE]



    this..


    Crank the engine until the mark on the damper aligns with the TDC or 0 degree mark on the timing tab and the engine is in the No. 1 firing position. This can be determined by placing your fingers on the No. 1 cylinder valves as the marks align. If the valves do not move, it is in the No. 1 firing position. If the valves move, it is in the No. 6 firing position (No. 4 on V6) and the crankcase should be rotated one more revolution to the No. 1 firing position.
    With the engine in the No. 1 firing position, the following valves can be adjusted:
    V8: Exhaust 1, 3, 4, 8
    V8: Intake 1, 2, 5, 7
    V6: Exhaust 1, 5, 6
    V6: Intake 1, 2, 3
    Back out the adjusting nut until lash is felt at the pushrod, then turn the adjusting nut in until all lash is removed. This can be determined by checking pushrod end-play while turning the adjusting nut. When all play has been removed, turn the adjusting nut in:
    1/2-11/4 additional turn (flat lifter)
    3/4-11/4 additional turn (roller lifter V8)
    3/4 additional turn (roller lifter V6)
    Crank the engine 1 full revolution until the marks are again in alignment. This is the No. 6 firing position (No. 4 on V6). The following valves can now be adjusted:
    V8: Exhaust 2, 5, 6, 7
    V8: Intake 3, 4, 6, 8
    V6: Exhaust 2, 3, 4
    V6: Intake 4, 5, 6


    With solid lifters i obviously didnt torque it past zero lash.. I think i used .022 on the intake and .024 on the exhaust.
    Quote Originally Posted by jetboatperformance View Post
    the ensueing fire would likely be extinguished by the sinking however

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