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Mercruiser 4.3 hard starting when warm fix

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  • Mercruiser 4.3 hard starting when warm fix

    I posted a while back about my merc 4.3 1991 engine being hard to start when warm. It always starts right up when cold, but after sitting for an hour it takes forever to start. This seems to be happening to a lot of you with this particular engine, and it is always blamed on vapor lock.

    I found a fix, at the help of the board members here, so i figured i'd share. I too, was determined it was vapor lock. Did all the things you guys have done to fix it... run the blower the entire time on the water, let it idle for a while before shut down, open engine compartment etc. NOTHING. Still took 15-20 seconds to start after it heated up.

    I found out through here it could be flooding after sitting, due to the wrong type of needle/seat being used, or something along those lines. I was told the next time i let it sit after it is warm, to hold the throttle at WOT when starting. Apparently it helps a flooded engine start. Sure enough, fired in about 2 seconds instead of 15 seconds. I also then pulled the flame arrestor and there was a little bit of gas running down the throat.

    I will probably just have the carb rebuilt at the end of the season, but it's good to know the problem is an easy fix.

    So before you go spending money on extra blowers, fuel coolers, check valves etc, check for engine flooding. Happy boating!
    1991 Regal Valanti 4.3 Litre V6


  • #2
    Re: Mercruiser 4.3 hard starting when warm fix

    Same things happens on my 4.3. As soon as you shut the engine off, (if you have the flame arrestor off), you can see the bowls fill with gas.

    No, it won't restart without giving a little throttle action (i.e. - you can't just turn the key to start it); I usually open the trottle to about 3/4 way, turn the key, and return to neutral upon firing. Never had a problem doing this.

    I'll probably resort to a carb rebuild at the end of this season as well.

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    • #3
      Re: Mercruiser 4.3 hard starting when warm fix

      Originally posted by Krapht View Post
      Same things happens on my 4.3. As soon as you shut the engine off, (if you have the flame arrestor off), you can see the bowls fill with gas.

      No, it won't restart without giving a little throttle action (i.e. - you can't just turn the key to start it); I usually open the trottle to about 3/4 way, turn the key, and return to neutral upon firing. Never had a problem doing this.

      I'll probably resort to a carb rebuild at the end of this season as well.
      Yeah it sucked for a while because the engine is very strong and its embarassing to take that long to start. But now she fires right up when the throttle is open.

      Another thing that i just realized. Something else that points to flooding was:

      After warming up the start times were:

      Sitting 0-20 minutes - Immediate start
      Sitting 30 minutes to 2 hours - 15 second start, or having to peg throttle
      Sitting 2 hours or longer - Immediate start
      1991 Regal Valanti 4.3 Litre V6

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      • #4
        Re: Mercruiser 4.3 hard starting when warm fix

        Mine was doing that last year so this spring I took the carb off, had it rebuilt and now it fires like a rocket cold or hot.

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        • #5
          Re: Mercruiser 4.3 hard starting when warm fix

          Originally posted by Harte3 View Post
          Mine was doing that last year so this spring I took the carb off, had it rebuilt and now it fires like a rocket cold or hot.
          Yep, I plan on doing it at the end of the season. Dont really feel like taking it out of the marina mid-season. Doesn't hurt anything just have to alter the starting ritual Starts in 2 seconds at 3/4 throttle.
          1991 Regal Valanti 4.3 Litre V6

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          • #6
            Re: Mercruiser 4.3 hard starting when warm fix

            Originally posted by ryanr623 View Post
            I
            I , to hold the throttle at WOT when starting. Apparently it helps a flooded engine start.!
            ryan623, you must not have been around before fuel injection was standard on all cars or owned a snowmobile or older 4wheeler or even an older outboard as that is standard practice engrained into my dna. The best thing when fuel injection on cars took hold was not having to play the flooded carb game. What makes our carbed I/O's tolerable is that we don't have to drive them at cold temps when a carb problem is really noticable. Carbs are amazingly still present on newer snowmobiles and so the frustration lives on.
            2003 Chaparral 183SS

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            • #7
              Re: Mercruiser 4.3 hard starting when warm fix

              Originally posted by jkust View Post
              ryan623, you must not have been around before fuel injection was standard on all cars or owned a snowmobile or older 4wheeler or even an older outboard as that is standard practice engrained into my dna. The best thing when fuel injection on cars took hold was not having to play the flooded carb game. What makes our carbed I/O's tolerable is that we don't have to drive them at cold temps when a carb problem is really noticable. Carbs are amazingly still present on newer snowmobiles and so the frustration lives on.
              You are correct, I am only 28. Even my jetski is a FI'd 4 stroke. I figured starting at WOT would make the flooding worse ha ha. Luckily bond-o and Don S. are around!
              1991 Regal Valanti 4.3 Litre V6

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