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  1. W

    Engine alignment problem

    Here it is. I removed both engines from my boat a couple years ago and just got to finishing and installing the new ones a couple weeks ago. First engine went in no problem. Minor adjustment needed but the alignment tool slides in. Engin 2 goes in and it appears to be sitting slightly too...
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    5.0 mpi to 383 conversion thoughts?

    Looking for ideas and concerns with this idea. I’ve got a pair of 5.0 mpi engines in my boat and want to go bigger. Looking at getting a pair of 383 stroker long blocks and swapping the mpi intake and all other parts over to the engines. Will the ecu work or would I need a new ecu for each? Can...
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    5.0 mpi backfiring through exhaust. Won’t start

    Engine serial number is m367508 2005 5.0 mpi Working on my new boat and the port engine is giving me trouble. Finally got gas to it and it sounds like it wants to start but only backfires through the exhaust periodically. My question is if this would be a possible symptom of spinning the motor...
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    5.0 mpi runs rough when wet

    Can’t seem to track this down but noticed when the engine gets wet it runs rough. Low power, poor fuel mileage. Checked plugs, wires, cap and rotor replaced twice. Good fuel. Clean filter. When I left the engine cover off and let everything completely dry for a few days it was able to run 20...
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    Bravo air operated drain.

    One of my engines on the new boat has this cylinder with air lines as part of the water pump. I broke the top line off removing it. Can I delete this system. My other engine just has the 2 water lines on the back. What’s the purpose of this system?
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    Bravo 2 water pump impeller

    So I just purchased a boat with twin 5.0 mpi engines with bravo drives. My other boat has the same engine with an alpha one. Does the bravo drive have an internal impeller like the alpha one or is it just the water pump on the engine that needs service? What differences are there between the...
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    350 mercruiser stalling when shifted into gear

    My other boat project is giving me trouble. Got it running with help from here but now it shuts down when I go to shift it into gear. It’s a mercruiser 350 with the 2 barrel carb. Alpha one gen one drive. That’s all the info I currently have on this one. This is being tested on the hose in the...
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    5.0 mpi bogging and backfiring at high rpm

    Had my boat out for an offshore fishing trip. Ran 50 miles out no issue. Coming back about halfway it started dropping rpms and backfiring. It would then run ok for a bit then do it again. Then it cleared up and ran the last 15 miles with no issues. Fuel filter was good with no water or other...
  9. W

    Fuel pump issues

    So I’m helping someone with their new “free” boat. It’s a late 80’s model with a merc 350 with the thunderbolt v ignition and gen one alpha one drive. I can’t read the serial number anymore. Problem is that it started pretty readily after a tuneup and fluid change. Let it run a bit and it died...
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    Mercury wear pads missing cause of vibration?

    So for the moment I’ve got everything working as it should on my boat. Merc 5.0 mpi with an alpha one gen 2 behind it. My question is that at low rpm in gear the boat has a slight vibration to it that goes away with a little more rpm. The drive is a new sei marine unit but I’m pretty sure it did...
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    Where is this water coming from?

    Got her started. What have I got here?
  12. W

    Ignition wiring questions.

    I’ve got a bay liner trophy from 1998 with the 5.0 mercruiser engine and alpha one drive. Just getting it going for the season and nothing at the key. Battery is tested and good. The kill switch seems to be good. I attempted to jump it and leave it disconnected since I didn’t know if it was a...
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    5.0 mph belt routing

    Ok. Not sure what happened but I replaced my alternator and now the belt is too short. Lol. I’m sure I’m doing it wrong but can’t find any diagram where it’s correct. The motor is a 5.0 mph serial number 0m670725. I changed the pulley to the original one because the new one was bigger but still...
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    blocked manifold? 5.0 mpi mercruiser

    Just trying to confirm what ive already found before i order parts. Have had an overheating issue for a while now and think ive found it. Boat runs hot at higher rpms. Did the clear hose test. No bubbles. Did notice the last time out the left riser was too hot to touch but the right was...
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    Automotive vs marine thermostat

    So haven’t definitively solved my overheating problem but thought about the fact that I used an automotive 160 degree thermostat last spring and ran mostly in salt water with my raw water cooled engine. Is there any difference in the materials used or flow allowed? The motor specs are 2003 5.0...
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    mercruiser 5.0 mpi slowly overheating

    Got my boat out for a test run today and it runs great except that after about 30 minutes of running about 75% throttle it overheated. Shut it off for 3 minutes and restart. immediately cooled down. Ran a bit longer and the temp was slowly climbing again and I stopped but didnt shut it down...
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    Octane recommendation in 5.0 mph mercruiser

    I have been running 89 from the pump with ethanol bc I can find gas without it. I use Star tron additive to help with this. Is there any reason I couldn’t run 87 and get a little more? What’s everyone’s opinion on this?
  18. W

    Alpha one gen 2 bumped out of gear but stuck in gear?

    So i was cruising across the lake today at high speed and my drive sounded and felt like it shifted out of gear and back into gear suddenly while cruising. I immediately put it in neutral but the engine stalled. Cant turn like the drive is stuck in gear. I noticed recently that the drive...
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    98 Trophy 2352 top speed and fuel economy.

    So I finally got my motor back together and tested out several times on my local lake and I don’t think I could ask for more. It’s got the 5.0 mpi mercruiser with an alpha one drive running a 17 pitch revolution 4 prop and on the lake it’s topped out at 41 mph at 4700 rpm. At this speed I was...
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    5.0 mpi overheat at higher rpm.

    Finally got the heads back and on the boat. Runs great but at higher rpm it will overheat and wont cool off unless I shut the motor off for about 2 minutes and restart. Then the temp drops rapidly. Ive noticed if you are looking at the motor the left riser on the exhaust gets pretty warm...
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