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Shaking like a big block mopar

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  • Shaking like a big block mopar

    I just picked up a 1984 Stars and Stripes and have a diagnostic question: at idle the motor shakes, not really like a worrisome shake, but more like a 454 with a big cam at a red light. The motor sounds good and runs well , I did notice it puff out a little white smoke this morning when I started it up in my driveway. What could the shaking be? Soft mounts? Or maybe a tune? Its a ford 351 with 938 hours.

  • #2
    Originally posted by Czechmate View Post
    I just picked up a 1984 Stars and Stripes and have a diagnostic question: at idle the motor shakes, not really like a worrisome shake, but more like a 454 with a big cam at a red light. The motor sounds good and runs well , I did notice it puff out a little white smoke this morning when I started it up in my driveway. What could the shaking be? Soft mounts? Or maybe a tune? Its a ford 351 with 938 hours.
    It can't run rough AND good of it doesn't have any modifications.

    Did you remove the plug wires recently? Re-check the firing order and make sure the plugs, wires, cap & rotor are in good condition. If they're all OK, check for spark on all cylinders using a spark tester, not just a timing light. If that's OK, check the compression/cylinder leakdown.

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    • #3
      351 idle

      It should run like this:
      Attached Files

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      • #4
        That puff of white smoke at start up is probably valve guide seals starting to leak.
        -Tim

        Making boomers great again!! Boomin'

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        • #5
          Sounds like carb issues. Choke partially closed, float level, leaky power valve? I would remove the flame arrestor and make sure the choke butterfly is opening fully. Also after letting it run for a bit switch it off and look down the carb throat for dripping fuel, there should be none.

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          • #6
            Originally posted by tph View Post
            It should run like this:
            Ill post a video of mine running soon for comparison.

            Originally posted by whiskeyriver View Post
            Sounds like carb issues. Choke partially closed, float level, leaky power valve? I would remove the flame arrestor and make sure the choke butterfly is opening fully. Also after letting it run for a bit switch it off and look down the carb throat for dripping fuel, there should be none.
            The last owner did say that the carb floods periodically, but he has been driving this boat this way for years and said he hasn't noticed anything troublesome. I think he may have gotten comfortable with the way it runs, and thus thinks of it as normal.
            Ill check the carb out and let you know what I find.

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            • #7
              Originally posted by Czechmate View Post
              Ill post a video of mine running soon for comparison.



              The last owner did say that the carb floods periodically, but he has been driving this boat this way for years and said he hasn't noticed anything troublesome. I think he may have gotten comfortable with the way it runs, and thus thinks of it as normal.
              Ill check the carb out and let you know what I find.
              Sounds like you may have a needle & seat going. You can also have problems if fine crud id getting through your filter and getting stuck in the needle & seat. If it wants to flood when it's running, if you put it in gear and crack the throttle open for a couple seconds, this will usually wash the crud out so the needle & seat can close properly.

              Have you checked for a vacuum leak at the carb and the spacer? When it's idling, spray some carb cleaner around the base of the carb and spacer. If the engine speed increases, you have found your leak.

              Have you looked at your spark plugs to see the color? That may show a rich or lean condition and give you something to chase.

              If you do need a car rebuild, I would be happy to do it for you. I have done a lot of carbs for members here over the last few years.
              CUSTOM WHEEL & TIRE PACKAGES
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              CUSTOM DECALS - EMAIL FOR MORE INFO

              $125 LED TRAILER LIGHT PACKAGE - FREE SHIPPING
              REBUILDING HOLLEY MARINE CARBS - $350 DELIVERED
              REBUILT COMPLETE MARINE HOLLEY 4160 CARBS $549 DELIVERED
              Email - [email protected]

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              • #8
                Originally posted by thatsmrmastercraft View Post
                Sounds like you may have a needle & seat going. You can also have problems if fine crud id getting through your filter and getting stuck in the needle & seat. If it wants to flood when it's running, if you put it in gear and crack the throttle open for a couple seconds, this will usually wash the crud out so the needle & seat can close properly.

                Have you checked for a vacuum leak at the carb and the spacer? When it's idling, spray some carb cleaner around the base of the carb and spacer. If the engine speed increases, you have found your leak.

                Have you looked at your spark plugs to see the color? That may show a rich or lean condition and give you something to chase.

                If you do need a car rebuild, I would be happy to do it for you. I have done a lot of carbs for members here over the last few years.
                So I did a quick run through and everything looked fine. The guy had the rotor and cap, wires, and plugs changed three years ago, and the boat has had minimal use since. I found a local shop who is going to do a more detailed diagnostic, so ill be waiting for those results!

                Ive got another question: After reading through the original manual that came with the boat, it states "Unleaded fuel should not be used". So I'm assuming unleaded fuel has been used in this boat for quite some time. I know with older motors the lead helps reduce cam wear correct? Is it really necessary to now add the lead additive available in stores? Or is it fine to keep adding in 93 octane unleaded?

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                • #9
                  Originally posted by Czechmate View Post
                  So I did a quick run through and everything looked fine. The guy had the rotor and cap, wires, and plugs changed three years ago, and the boat has had minimal use since. I found a local shop who is going to do a more detailed diagnostic, so ill be waiting for those results!

                  Ive got another question: After reading through the original manual that came with the boat, it states "Unleaded fuel should not be used". So I'm assuming unleaded fuel has been used in this boat for quite some time. I know with older motors the lead helps reduce cam wear correct? Is it really necessary to now add the lead additive available in stores? Or is it fine to keep adding in 93 octane unleaded?
                  Yeah, supposedly unleaded will prematurely wear valve seats. Personally I think you're alright. I find it much more important to protect from ethanol. Use an additive to combat it if non ethanol fuel is not readily available.

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                  • #10
                    Valvoline VR1 20W/50 has the needed additive package containing Zinc to provide the lubricant for the Ford's cam and lifter needs. There are some other oils as well, but this is my oil of choice.
                    CUSTOM WHEEL & TIRE PACKAGES
                    sigpic

                    CUSTOM DECALS - EMAIL FOR MORE INFO

                    $125 LED TRAILER LIGHT PACKAGE - FREE SHIPPING
                    REBUILDING HOLLEY MARINE CARBS - $350 DELIVERED
                    REBUILT COMPLETE MARINE HOLLEY 4160 CARBS $549 DELIVERED
                    Email - [email protected]

                    Comment


                    • #11
                      Lead was used in gasoline to lower combustion temperatures. Hardened valve seats were implemented in engines to withstand the higher combustion temps of unleaded gasoline. Using unleaded gas in a "pre-unleaded" engine can cause valve and valve seat damage. Personally, I would pull the heads and have a machine shop install hardened valve seats and new valves. Shouldn't be more than a few hundred bucks. Until then I would definitely use a lead substitute/additive in the gas.
                      If you feel this damage has already occurred in your engine, an easy test is to remove the valve covers and rocker arms and lay a straight edge across the tops of the valve stems. Any deviation in valve stem height is a sign of trouble.

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