Ok, I think it's my first time posting. I'm far from a mechanic but do have some basic knowledge. I bought a mercruiser 5.7 carb motor from a boat yard. Ran gd for about 8 trips fishing at sea all day. Started cutting out. So here is what it's doing. It runs gd for about 100 yards then cuts out. I've changed cap, rotor and upgraded sensor. Motor starts with tap of key. Idles great, revs hd and strong on ear muffs. Once under load it will cut out after about 100 yards at full throttle then has huge miss. I've checked everything I can. Once it cuts out at full throttle, you can push the outdrive button dow. Ir up or any electrical item and it picks up and runs strong. I was told alternator was bad. Changed and it ran about a mile gd and back at same issue. Has a tb4 ignition system. I've checked and cleaned every ground. Getting all current volts it should. Unless my friend missed something. It had a coil that said use with external resistor. But after alot reading g thise were only for point system . Mine is not a point system. So I bought a gm 12volt coil. Still does the same thing. I dont know what else to check a d I'm not very smart on tte voltage testing stuff. It runs great in neutral and revs gd and strong. Coil does feel a little hot that prob should. Now I had this motir installed by a boat mechanic. He used a low pressure electric fuel pump and connected tte positive to the + on coil. Said be has always done that. It ran gd for about 8 trips or so before having this issue. We only have one mechanics shop here and they only work on newer stuff and original. Since the motor is not original they wont touch it as they dont know what's been done. But like I said. It runs gd for about 100 yards the cuts out at any speed or rpm. But if you hold outdrive button it will run great til u let go. Also if I push bilge pump button it get lil more power. But the outdrive button seems to take away the issue the best. I know it's something shorting out. I'm lost. Been at it for almost 2 yrs with different mechanic minded friends. Anyone ever have an issue like this.
John
John