98BaronMag
New member
Hello all,
I've been pouring over dozens of old threads the last few weeks trying to sort out some issues I'm having, but was mostly just trying small, inexpensive fixes. After this weekend, I decided to find a shop to work on my boat. Unfortunately, no one in my area particularly wants to work on a sterndrive, especially one that's going to take some hours troubleshooting. It seems I'm on my own here, so I'd like to dig into the project myself. I thought starting a thread for my specific issues would be the best way to find the most pertinent information. I'm an alright shade tree mechanic, but have no experience in marine scenarios. Hoping you guys can help guide me in the right direction.
My boat is a 1998 Lund Baron Magnum with a Mercruiser 5.7L TBI Alpha 1 sterndrive. Since I bought the boat last year it has always seemed low on power. When I initially bought it, top speed at WOT was about 40mph at 3600 rpm trimmed up as much as possible without prop blowout. This was on a 19p Mercury Black Max prop. I thought perhaps I was overpropped and that the aluminum prop was blowing out prematurely. I switched to a 17p Mercury Mirage Plus. This brought my WOT rpms up to about 4000 - still about 40mph. I became more concerned about this lack of power towards the end of last season, when the motor began to backfire occasionally at cruising speed and developed a 'knocking' on acceleration (starting in the 1500-2000 rpm range) I cannot discern if the knock is coming from the engine or the drive but it is loudest when accelerating, once at cruise speed it is not as noticeable. With those issues in mind, I took my boat in last year and asked the shop to go through it completely to try and figure out where this was coming from. They changed all the fluids and spark plugs (which they said were the originals as they had motor paint on them!) and told me plug wires and distributor were fine and they found no other issues. This year, when I took it out for the first time, the backfiring had worsened, making 5 or 10 pops in rapid succession instead of just one or two as it had been last year. I decided to take matters into my own hands and do some digging. I replaced the fuel/water separator and checked the distributor cap. The pins inside the cap as well as the rotor tip were severely corroded - not a bare spot of metal to be seen. Distributor cap also had original motor paint on it. Satisfied I had found the issue, I ordered a new cap and rotor and installed them. This weekend, I had the boat out for testing. The knock, backfire, and low power conditions all persist, but only under load. In neutral the engine runs fine, perhaps a bit of a rough idle, but especially over 1000rpms it sounds smooth and normal. In addition, it starts much harder than before in certain scenarios since replacing the cap/rotor and fuel/water separator. If the motor has been off for 10 minutes or more, it will crank and sounds like its firing but takes 20ish seconds and a bit of throttle to get it going. If you shut it off it will immediately restart without issue. I'm thinking perhaps the hard start condition has come from some air in the fuel system since replacing the fuel/water separator, but I read in other threads that the TBI has no bleeder valve and is supposed to be self-bleeding.
I'm looking for some starting points to dig into these problems. As of now, I'm planning to loosen the fuel line fitting at the throttle body and try to pump any air out of the line there. For the other problems, I'm much less sure of a starting point. I'm thinking about checking timing, compression, fuel pressure, exhaust flappers, replacing plug wires, and checking my work on the distributor and fuel filter, but this is a very shotgun approach and I'm sure to waste a lot of time and potentially money doing it this way. I'm hoping you kind folks can give me a sense of direction on where to start for the highest probability of sorting this out.
S/N on the motor is 0L049032 if that helps anyone identify exactly what I've got.
Thanks,
-Marcus
I've been pouring over dozens of old threads the last few weeks trying to sort out some issues I'm having, but was mostly just trying small, inexpensive fixes. After this weekend, I decided to find a shop to work on my boat. Unfortunately, no one in my area particularly wants to work on a sterndrive, especially one that's going to take some hours troubleshooting. It seems I'm on my own here, so I'd like to dig into the project myself. I thought starting a thread for my specific issues would be the best way to find the most pertinent information. I'm an alright shade tree mechanic, but have no experience in marine scenarios. Hoping you guys can help guide me in the right direction.
My boat is a 1998 Lund Baron Magnum with a Mercruiser 5.7L TBI Alpha 1 sterndrive. Since I bought the boat last year it has always seemed low on power. When I initially bought it, top speed at WOT was about 40mph at 3600 rpm trimmed up as much as possible without prop blowout. This was on a 19p Mercury Black Max prop. I thought perhaps I was overpropped and that the aluminum prop was blowing out prematurely. I switched to a 17p Mercury Mirage Plus. This brought my WOT rpms up to about 4000 - still about 40mph. I became more concerned about this lack of power towards the end of last season, when the motor began to backfire occasionally at cruising speed and developed a 'knocking' on acceleration (starting in the 1500-2000 rpm range) I cannot discern if the knock is coming from the engine or the drive but it is loudest when accelerating, once at cruise speed it is not as noticeable. With those issues in mind, I took my boat in last year and asked the shop to go through it completely to try and figure out where this was coming from. They changed all the fluids and spark plugs (which they said were the originals as they had motor paint on them!) and told me plug wires and distributor were fine and they found no other issues. This year, when I took it out for the first time, the backfiring had worsened, making 5 or 10 pops in rapid succession instead of just one or two as it had been last year. I decided to take matters into my own hands and do some digging. I replaced the fuel/water separator and checked the distributor cap. The pins inside the cap as well as the rotor tip were severely corroded - not a bare spot of metal to be seen. Distributor cap also had original motor paint on it. Satisfied I had found the issue, I ordered a new cap and rotor and installed them. This weekend, I had the boat out for testing. The knock, backfire, and low power conditions all persist, but only under load. In neutral the engine runs fine, perhaps a bit of a rough idle, but especially over 1000rpms it sounds smooth and normal. In addition, it starts much harder than before in certain scenarios since replacing the cap/rotor and fuel/water separator. If the motor has been off for 10 minutes or more, it will crank and sounds like its firing but takes 20ish seconds and a bit of throttle to get it going. If you shut it off it will immediately restart without issue. I'm thinking perhaps the hard start condition has come from some air in the fuel system since replacing the fuel/water separator, but I read in other threads that the TBI has no bleeder valve and is supposed to be self-bleeding.
I'm looking for some starting points to dig into these problems. As of now, I'm planning to loosen the fuel line fitting at the throttle body and try to pump any air out of the line there. For the other problems, I'm much less sure of a starting point. I'm thinking about checking timing, compression, fuel pressure, exhaust flappers, replacing plug wires, and checking my work on the distributor and fuel filter, but this is a very shotgun approach and I'm sure to waste a lot of time and potentially money doing it this way. I'm hoping you kind folks can give me a sense of direction on where to start for the highest probability of sorting this out.
S/N on the motor is 0L049032 if that helps anyone identify exactly what I've got.
Thanks,
-Marcus
