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Bogs right off idle with full throttle

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  • Bogs right off idle with full throttle

    I have a 85 mcm 140 with rochester carb and alpha 1. My idle was too low and I fixed it by adjusting the throttle cable. The motor runs great thoughout the entire rpm range except for when coming off idle to fast full throttle (pulling skier). From forward position idle to full throttle the rpms will pick up slightly. It will then either stall or bog down to 200 rpms then shoot up like it's suppose to. If i slowly run into it(without skier) its fine. Also other random times at full throttle mostly, it will bog sometimes just alil. It Loses some rpm then gains it back. It repeats itself for 20 seconds then will stop. Other times it will choke itself out to a stall.

    I'm thinking it's a fuel issue as when I pump the throttle sometimes gas isn't coming out of the jets.


    Also yesterday I was on full plane. Engine died out. No gas coming out of jets in carb. Took off fuel pump filter. Looked clean and then put it back on tight. Started right up. I had a tube tied to back of boat and there was a weezing sound/hum. Thought it was the tube making noise from wind. Maybe the fuel pump filter retainer wasn't on tight enough. And fuel pressure excaped?

    I'm thinking I'm gonna need to do a carb. But before I rebuild. What other things could it be? And or should I attempt to clean? What should I use to clean fuel lines/ components?

    This boat is new to me. So I don't have previous maintance records
    1988 Wellcraft 170 classic
    1985 140 3.0L mercruiser
    alpha 1 gen 1
    http://forums.iboats.com/showthread.php? I NEED HELP!!! any is better than none


  • #2
    Re: Bogs right off idle with full throttle

    you don't adjust idle speed by adjusting the cable, you adjust it with the idle speed screw on the carb setting the idel speed to spec - then you set the idle mixture screws to attain best possible idle

    when was the last full tune-up??

    if you are losing fuel pressure you wouldn't hear air hissing, you would see fuel leaking

    have you checked fuel pump pressure??

    if there is no blast of fuel upon throttling, either there is no fuel in the accel pump well or the umbrella is shot - if fuel pump pressue is okay (4 psi steady at idle, 5-7 at 2000 rpm), i would suspect a faulty carb, time for a rebuild
    Sometimes when people try to save a penny, they end up spending a dollar

    It is best to fully understand how to properly operate, inspect, troubleshoot and repair your equipment

    Comment



    • #3
      Re: Bogs right off idle with full throttle

      Where is the idle speed screw? I know where the two idle mixture screws are infront of the carb.
      1988 Wellcraft 170 classic
      1985 140 3.0L mercruiser
      alpha 1 gen 1
      http://forums.iboats.com/showthread.php? I NEED HELP!!! any is better than none

      Comment



      • #4
        Re: Bogs right off idle with full throttle

        check the adults only/must have info stickys for mercruiser info to find a link to download your OEM engine manual

        in the manual you will find all the carb adjustment/tune-up specs for your engine
        Sometimes when people try to save a penny, they end up spending a dollar

        It is best to fully understand how to properly operate, inspect, troubleshoot and repair your equipment

        Comment



        • #5
          Re: Bogs right off idle with full throttle

          found the idle speed screw, my idle was off, around 200 rpm. it wasnt when we first ran the boat this year, it was normal idle, and we didnt experience the bog. so maybe with that screw properly adjusted it will also fix the bogging issue
          1988 Wellcraft 170 classic
          1985 140 3.0L mercruiser
          alpha 1 gen 1
          http://forums.iboats.com/showthread.php? I NEED HELP!!! any is better than none

          Comment



          • #6
            Re: Bogs right off idle with full throttle

            Fixed and adjusted idle speed. Still bogs out going from right off idle to full throttle. Is there a thing I can adjust to fix that? Lean or rich? Cleaned the fuel pump. Carb inlet screen and new fuel filter so far.
            1988 Wellcraft 170 classic
            1985 140 3.0L mercruiser
            alpha 1 gen 1
            http://forums.iboats.com/showthread.php? I NEED HELP!!! any is better than none

            Comment



            • #7
              Re: Bogs right off idle with full throttle

              Is it possible to fix the bog by adjusting the 2 idle mixture screws? I havent adjusted them at all since the boat idles well and sounds good. But maybe some minor adjustments will help. Bog can be created by a lean condition right? So I would want to tighten the screws? Or do I have it backwards? Would trying this even help? Or am I in it for a carb rebuild? I don't mind if I am. Just trying to troubleshoot things down the list from easiest and cheapest to more complicated and expensive
              1988 Wellcraft 170 classic
              1985 140 3.0L mercruiser
              alpha 1 gen 1
              http://forums.iboats.com/showthread.php? I NEED HELP!!! any is better than none

              Comment



              • #8
                Re: Bogs right off idle with full throttle

                Originally posted by Rellik546 View Post
                Is it possible to fix the bog by adjusting the 2 idle mixture screws? I havent adjusted them at all since the boat idles well and sounds good. But maybe some minor adjustments will help. Bog can be created by a lean condition right? So I would want to tighten the screws? Or do I have it backwards? Would trying this even help? Or am I in it for a carb rebuild? I don't mind if I am. Just trying to troubleshoot things down the list from easiest and cheapest to more complicated and expensive
                Accelerator pump on the carb would be my guess. Pump gives extra shot of fuel on throttle increase to overcome the extra shot of air before main metering reacts. Adjust carb idle per manual, paying attention to the accelerator pump adjustment, if it is adjustable (some are and some aren't). If that doesn't do it, pump may be NG and you'll need a carb rebuild. All the kits include a new accelerator pump.
                '92 Chaparral 2550 SX Sport
                454 BBC Mercruiser Bravo 1
                Tow with '04 F150 Larriat SuperCab 4x4 5.4 Triton
                US Coast Guard Aux.

                Comment



                • #9
                  Re: Bogs right off idle with full throttle

                  You can adjust the accelerator pump on the Qjet by pushing the rolled pin that holds the arm "in" towards the carb, remove the arm and move the rod to the inside hole on the arm. Reinstall and that should solve the issue. It will give you the extra shot of fuel you need to get you out of the hole
                  Todd 22' STARCRAFT SS V5 200hp

                  Comment



                  • #10
                    Re: Bogs right off idle with full throttle

                    its not a qjet, and this model doesnt have the adjustable accelerator pump arm. i picked up a rebuild kit, new fuel filter and gasket,(i had only cleaned the old one), and a fuel water separator. i also noticed my alternator brace had broke again, and then found that a replacement bottom bracket had been updated since my engine release date. it has 2 supports instead of 1, and i guess this keeps the top brace from breaking. so i picked up a brace and that upgraded bottom bracket as well as a new belt.

                    hopefully this will take care of all my problems. i generally run 93 octane in the boat, my dad seems to think that because gas is so expensive that less people buy it and it sits in the tanks longer at the station thus more likely to collect water. even if this isnt true, or the gas doesnt sit long the fuel water separator is a good idea. the tank was removed and drained when i redid the deck and stringers this winter. but i think water got into it when it rained one day and the fuel fill hose was left connected to the tank but not the fill neck. water may have got in. i also want to check my fuel pick up screen but cant seem to figure out how to remove it from the tank. its a plastic tank, and has a large diameter but thin profile nut on the fuel pick up unit. i was told not to remove or loosen this nut. that your suppose to undo the gas line, and then twist the barb until its undone and pull the whole thing out. I just dont want to screw this up. and have to rip my deck up to replace the tank. so any tips or pointer would help
                    1988 Wellcraft 170 classic
                    1985 140 3.0L mercruiser
                    alpha 1 gen 1
                    http://forums.iboats.com/showthread.php? I NEED HELP!!! any is better than none

                    Comment



                    • #11
                      Re: Bogs right off idle with full throttle

                      How do u properly remove the fuel pick up from the tank?
                      1988 Wellcraft 170 classic
                      1985 140 3.0L mercruiser
                      alpha 1 gen 1
                      http://forums.iboats.com/showthread.php? I NEED HELP!!! any is better than none

                      Comment



                      • #12
                        Re: Bogs right off idle with full throttle

                        so i removed the fuel pick up tube. it was easy, well it was simple. it was screwed in tight as hell and took some might to remove it. when i removed the tube it didnt have a screen or sock. should i put one on? i also installed the fuel water separator. i had my brother pump the throttle while i looked into the carb. i get 2 solid streams of fuel...so im now im thinking my accelerator pump is fine. i will most likely be doing the rebuild anyways to remove build up. but if its not the accelerator pump what is it? i was always told to adjust the timing before adjusting a carb. so maybe it is in the timing. maybe in the points gap, or dwell angle. any ideas?
                        1988 Wellcraft 170 classic
                        1985 140 3.0L mercruiser
                        alpha 1 gen 1
                        http://forums.iboats.com/showthread.php? I NEED HELP!!! any is better than none

                        Comment



                        • #13
                          Re: Bogs right off idle with full throttle

                          Did you ever figure this one out? I;m having the same issue

                          Comment



                          • #14
                            Re: Bogs right off idle with full throttle

                            So I retested and I wasn't getting 2 streams. I rebuilt the car, and it appears they used a wrong gasket and a few parts were missing. A lock washer, gasket, and the new accelorator pump has a couple extra parts that the old one didn't have at all. I dipped it in berrymans what it was stripped for a few hours then sprayed it out with compressed b-12. In a couple days I will reinstall it and see if it runs. I will say the rebuild was extremely easy with the help of the mercruiser manual. I had to use manual 3. Because manual 10 doesn't have the Rochester carb. Only the mercarb break down. I'm glad I rebuilt it. There was tarnish and gunk built up. So hopefully this will solve all if not some of my issues
                            1988 Wellcraft 170 classic
                            1985 140 3.0L mercruiser
                            alpha 1 gen 1
                            http://forums.iboats.com/showthread.php? I NEED HELP!!! any is better than none

                            Comment



                            • #15
                              Sign up today
                              Re: Bogs right off idle with full throttle

                              FYI - I had this EXACT same issue on my 198 Mercruiser and it was resolved by a complete Carb rebuild. I am not 100% certain what was all done on the rebuild as I don't have my receipt in front of me, but I know they rebuilt it completely.

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