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Engine wont start after removing carb

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  • Engine wont start after removing carb

    I have a 1985 mercruiser 120 that I've been trying to get seaworthy after an overheat. I had the boat running after the initial set of repairs, but it overheated again at WOT during the first maintenance run. The second overheat was not severe at all: I was only in the water for 15 minutes and cut power as soon as I saw the temp guage rise to 175. it cooled quickly at idle. The engine turned over again easily (and ran fine) once I got the boat back home and flushed the engine. Something I did is keeping the engine from starting now... here is the list of things done to address the overheating issue:

    Replaced the thermostat.
    Replaced the exhaust elbow (due to moderate buildup inside)
    I removed the carb in order to remove the exhaust elbow riser. (cleaned riser)
    Replaced the exhaust elbow boot
    Replaced the exhaust shutter (flapper)

    Put it all back together, engine would not start. Cranks fine, Sparks fine, it ran (and started) fine before, so I assumed I did something to the carb when I removed it.

    Took the boat to a mechanic to tell me what I did wrong. Mechanic tested the Fuel Pump and told me that it was letting air into the fuel, and should be replaced. I retrieved the boat and ordered a new fuel pump.

    I installed the new fuel pump, Engine still doesn't start. Replaced spark plugs. Engine cranks fine, Sparks fine, and now no reason to suspect a faulty fuel pump. I'm back to assuming that I somehow did something bad when I re-installed the carb, but since its 4 bolts and the throttle connections, I'm not too sure how I could have messed it up.

    I assume my compression is fine since the engine turned over and ran smoothly before I removed the carb.

    When removing the flame arrestor and looking into the carb, I can see that fuel is in the jets, but I've reached the limit of my carb troubleshooting ability.

    I'm thinking that I must have messed up something really basic. The carb is a 2 valve rochester with an electric choke. The valve flaps are sitting closed at the bottom of the carb. The only other thing of note is that the screw that rides the cam responsible for the choke plate position was not in the right position when I removed the carb, and I am not sure how thats supposed to be, other than somewhere on the cam.

    Any help or suggestions are greatly appreciated! Thanks-


  • #2
    Re: Engine wont start after removing carb

    Does the choke operate properly? IE: closed when engine cold. You can also pour a few teaspoons fuel down the carb and see if that mkes a difference.

    Comment



    • #3
      Re: Engine wont start after removing carb


      "I assume my compression is fine since the engine turned over and ran smoothly before I removed the carb. "


      Hey I'm no expert so I checked the troubleshooting guide for my Mercrusier1985-1989 4 cylinder GM Engine under "Engine Cranks Over But Will Not Start or Is Hard to Start".

      I'm sure you know this but it says if you have fuel, spark and compression arriving in the right order the engine should start. Could it be possible the overheating incidents have damaged your engine? If you run a compression test you could rule that one out. I've spent a career troubleshooting electical systems and I learned along time ago not to assume anything or "assume" can make an A** out of U & ME. Good luck.
      Summer Breeze
      1987 Sea Ray Sorrento S24
      5.7L Mercuiser Alpha One

      Comment



      • #4
        Re: Engine wont start after removing carb

        Originally posted by JeremyL View Post
        ......The carb is a 2 valve rochester with an electric choke. The valve flaps are sitting closed at the bottom of the carb. The only other thing of note is that the screw that rides the cam responsible for the choke plate position was not in the right position when I removed the carb, and I am not sure how thats supposed to be, other than somewhere on the cam.

        Any help or suggestions are greatly appreciated! Thanks-
        The bottom valve flaps (throttle butterflies) are supposed to be (almost) closed. The upper plate is the choke, is that closed when the engine is cold?
        If not, it won't start, unless you vigorously pump the throttle, or dump a couple ounces of raw gas into the carb.

        That screw is not "responsible for the choke plate position", the electric module does that. The screw is the fast idle adjustment, it will be at maximum deflection when engine is cold, dropping off the steps as the engine warms.

        I think you may just have a linkage off or jammed.

        Comment



        • #5
          Re: Engine wont start after removing carb

          Thanks for the replies-

          Reply 1: I am not sure if the choke is functioning properly, but thanks for letting me know that it needs to be closed when cold. : ) That at least tells me that I should set the adjustment screw on the cam in a position that keeps the choke plate closed.

          Reply 2: Compression test... I have the service manual too, but as of yet, no compression gague. I'll be getting one if I can't get the engine to turn over, but don't know how the engine would start and run fine prior to carb removal, then have a compression problem after.... Can't rule compression out as its #4 on the "troubleshoot startup" list, but I'd sure like to rule out "I screwed up the carb" before buying tools for a potentailly unrelated problem. Typing that out... guess I'll go price out a compression gague.

          Comment



          • #6
            Re: Engine wont start after removing carb

            @ Wire2:

            I will make sure that the choke plate is set to be closed. Its been open during my troubleshooting.

            Can you explain what you mean when you say you "think I have a linkage off or jammed" ?

            Comment



            • #7
              Re: Engine wont start after removing carb

              Maybe take the choke housing off and see if the bimetallic spring is still in one piece if it's not closing.

              Comment



              • #8
                Re: Engine wont start after removing carb

                I had the same thing happen to my boat (Chevy 454) and it took me three Sundays, a fuel pump check, a carb check, a new coil, and lots of french to sort out. I had one of the distributor posts shorting to the center post and robbing the other spark plug leads of juice, leading to a constant spark in the offending cylinder and weak spark in the remaining seven. When I noticed the 'way too frequent' sparking in that one lead, I disconnected it and the engine started on the remaining seven cylinders. When I reconnected it, no start. I traced the lead to the cap and found a VERY SUBTLE carbon line between the center post and the offending lead that indicated the trail of the short. I replaced the cap (that I had previously inspected), and everything was fine. Of course, if this happens everything in your ignition system checks out fine. I don't know if this can happen in an electric distributor, probably not. Still, I assume you've checked the spark going to each cylinder (put a spare plug in the respective lead you've pulled off the cylinder and touch the base to the block with those ruberized pliers designed to hold 'hot' plugs) and have someone crank the engine. They should all spark at about the same rate. If you spray ether/starter spray down the open throat of the carb and it doesn't even start temporarily, there is a spark issue. Bad compression will make an engine run badly but usually they still start. Let us know what it turns out to be, please. We've all been there!

                Robodoc

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                • #9
                  Re: Engine wont start after removing carb

                  Remove the flame arrestor and while holding the choke open, have someone pump the throttle a few times. If you don't see fuel squirt from the accelerator pump nozzles, the engine is not getting fuel. If you replaced the fuel pump, do you have the fuel lines on the correct ports (in to in, out to the carb). Did you make sure the arm on the fuel pump is in the correct position.

                  If the engine started fine before, leave the choke alone until you do get the engine started. Then let it cool over night and set it when the engine is stone cold. DO NOT attempt to set the choke on a warm engine.

                  Comment



                  • #10
                    Re: Engine wont start after removing carb

                    Originally posted by Silvertip View Post
                    Remove the flame arrestor and while holding the choke open, have someone pump the throttle a few times. If you don't see fuel squirt from the accelerator pump nozzles, the engine is not getting fuel. If you replaced the fuel pump, do you have the fuel lines on the correct ports (in to in, out to the carb). Did you make sure the arm on the fuel pump is in the correct position.

                    If the engine started fine before, leave the choke alone until you do get the engine started. Then let it cool over night and set it when the engine is stone cold. DO NOT attempt to set the choke on a warm engine.
                    Thanks Again for the replies, I'll be working on this shortly and will report today's findings...

                    I did make certain that the new fuel pump is connected properly to its in/out tubes, but you mention making sure the arm on the pump is in the correct position... The mechanic who removed the old pump said the same thing, indicating that it needed to be in the 'up' position. When handling the new pump, I didn't see a way to change the position of the arm at all: the arm is held in position by a spring, and pushing on the arm manually does force air through the tubes, but the arm always returned to its resting position due to the spring. Even the old pump behaves this way, so I don't know how I can mess that up. Do you mean that I should make sure the arm is in the correct position as it sits inside the engine cavity? If so, how do I verify that?

                    I will perform the "throttle pumping" test, and adjust the choke plate to rest closed before trying to start it. If it still fails, I'll move on to the in-hand sparkplug test and will report back.

                    Comment



                    • #11
                      Re: Engine wont start after removing carb

                      Ya put some fuel in the carb and see what that does. If all is hooked up well then u should get a cough
                      1985 Wellcraft 228 Sportsman
                      1989 Wellcraft Eclipse 4.3 merc

                      Comment



                      • #12
                        Re: Engine wont start after removing carb

                        Have you tried to use starting fluid on it just to see if it will start that way. if it wont start or even attempt to start its not a fuel problem....or the plates at the bottom of the carb are not opening. You can check those without help just move the throttle and see if the butterflies open up if they dont then you have either a cable issue or a linkage issue.....good luck
                        1975 Reinell 24'
                        Cuddy Cabin
                        Mercruiser 888

                        Comment



                        • #13
                          Re: Engine wont start after removing carb

                          Today's report: Started work to find the carb's thermostat housing oddly warm. Oh Good. I not only left the battery switch set to All last night, but I also somehow managed to leave the ingnition in the 'On' position. <sigh>

                          Anyway, armed with the knowledge that the choke plate needs to be in the closed position when cold, I was able to determine that the flat coil spring inside of the carb's thermostat was not hooked to the choke plate lever, resulting in the choke plate staying wide open. I re-hooked the coil spring around the lever.

                          Of course, I now don't know if that's my only problem becasue the batteries lost enough charge overnight that the sound it makes when it cranks makes you think that the batteries need to be charged.

                          I did pump the throttle a bunch of times and looked into the carb and found a nice little puddle of gas seeping down past the throttle butterflies, so I think I'm good there.

                          Off to charge the two batteries, will report once they're able to crank things right.

                          Comment



                          • #14
                            Re: Engine wont start after removing carb

                            After charging the batteries, I'm back to square one, and I admit defeat. Whenever I can afford it, I will take it back to the mechanic and have him figure out whatever issue(s) are keeping the engine from turing over.

                            I did look at the interior of distributror cap. Its in excellent condition. Clean copper points with only slight blackening at the initial contact point as the rotor spins.

                            I tried putting started fluid into the carb. No effect.

                            I'll certainly report back what the mechanic tells me the problem is once he gets it running. Thanks to you all for your suggestions.

                            Comment



                            • #15
                              Sign up today
                              Re: Engine wont start after removing carb

                              Whe you removed all parts during replacement, you didn't:

                              1) Remove the spark plug wires and get them in the wrong sequence?

                              2) Accidentially trip the ignition circuit breaker?

                              3) Knock any connection off of the coil?

                              4) Remove the safety lanyard from the ignition switch?

                              Just a couple more places to check...
                              2001 Carver Voyager 374 'Stick's Competition'

                              Something tells me I should be on the water....

                              If I answer your upholstery questions, it's only because I've been doing it 20+ years...

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