Bogging down in mid-rpms and backfiring occasionally - Help Appreciated

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by Texan, Sep 13, 2020.

  1. Texan

    Texan New Member

    Sep 12, 2020
    180 BR
    2000 model
    3.0l w Alpha Gen 2
    The family bought our first boat this year, my Dad had one for a short period 10+ years ago, we took a few rides when the kids were younger. In the last two years we rented boats for high dollar during holidays so we just decided to take the plunge at a time when "buying" is crazy insane.

    Our new-to-us 2000 Sea Ray 180 BR looked to be in cosmetically good condition for it's age - got the story from the previous owners and for the price we paid I would say we took a big gamble on the operability being that we didn't even do a water test before buying. Folks were lining up to buy it - I'm not exaggerating - its just CRAZY TIMES right now.

    So - unlike automobiles, there is no maintenance records that came with the boat. I guess I'm old school cause I keep all my receipts, which I've begun a small collection of already with the SR-180-BR. The previous owners did say that the engine block had been replaced *the previous engine got water in it* and that the new engine had only 10 hours on it. The 1 receipt we got was for the remanufactured GM 3.0l marine engine in May of 2020 for $2k.

    So - the first 6 trips out I can report that the boat idles fine and top cruising speed is about 3200 RPM (thats full WOT) but it is sluggish overall and nearly dead in the mid-RPM zone. Usually from no-wake to getting on plane I have to push through the bogging down to high RPM and hope for no backfire. The backfires come and go but they are usually when the boat is under heavy load (max capacity of people and gear) and at its top end of RPM.


    I am mechanically inclined - so I replaced the impeller and gear oil week 1 (for peace of mind) and to be honest the temp gauge shows 190 degrees and I haven't solved that yet.

    Replaced the thermostat with a 160 degree

    I pulled the plugs and they were golden red in color - appeared to be running lean and hot.... The prior owner had NGK TR5 plugs which I believe are heat range rated at '5' while the NGK plug that is called for (BPR6EFS) is heat range rated at '6'.

    So I went with the AC Delco OEM plug (AC-MR43LTS) and replace the distributor cap and rotor while I am there. Plugs were gapped to .045" and the rotor and cap showed to be well used - again not sure how old but arc evident on pole location on rotor and the points were yellow and crusty.

    I noticed the wires and cap orientation were 90 degrees OFF (wires went to the right plugs for firing order). So I reoriented the distributor to the location shown in the Service Manual.

    YESTERDAY - finally got the boat started and began timing it. The spark arrestor plate said 2 degrees ATDC for the original engine so I tried that first. It was barely running (before cutting off at idle) and backfired as soon as trying to get on plane out of the marina. I then went for 1 degree BTDC which I am making sure to be in base timing mode for this so when you take the shunt off and restore the shift interrupt switch the 1 degree BTDC turns to ~ 12 degrees BTDC on idle. IDLE is a bit high - 900 RPM at this setting but the boat runs good in low RPM and I get improved top end performance (now able to cruise at 3400 RPM). It feels stronger.

    BUT - still have that darn bogging down in the mid rpm and I did get 1 backfire on the way back into the marina at top RPM at the 1 degree BTDC timing location.

    SO I'd appreciate the assist on this from your knowledge base and experienced owners - I'm sort of out of easy options with the boat and trust me I know it isn't running right especially for a block that only has 25 hours on it.

    CARBs are voodoo magic if you ask me but I would need some guidance on trying to restore the one I have to stock settings.

    Advance timing ? What is the timing supposed to read at 2500 or 2800 rpms ? I hear that some folks time their engine solely based on this and just sort of jot down what the initial timing (base timing) is. Is there a method that works best for checking this, seems like a two person ordeal either way but are you just using advanced throttle and sitting still and taking the reading or do you have to be underway and check it for an accurate (under load) reading.

    These are the only two ideas I've come up with to try next but I am all ears. IT has been tough to work with a reman block - the only info I was able to get is that its post 1990 GM 3.0l so I'm not sure if the original spark arrestor plate is valid anymore anyway and when buying parts its been a challenge because I don't have a Mercruiser serial number.

    Other particulars -

    Mercruiser Alpha 1 Gen II outboard

    Oil is at the right level and fresh

    Boat has a constant wet bilge - I don't believe it was stored on water cause it would have sunk by now....

    Also the previous owner states he did the engine work to put the new block and accessories back together. I rate him high marks on the electrics and wiring harnesses, they still look factory and I wouldn't have been able to tell at a glance that the engine was a reman BUT the bolts ON THE ACCESSORIES were all mostly finger tight - so I have been going back around and tightening up everything, we lost power at WOT and had no ignition power and through tracing of the line in the engine bay thats when I found the leads that connect to the slave solenoid of the starter had fallen off the pole because they didn't even have a nut on them...........

    The gauges don't work - just the tachometer but I am hoping it is accurate. Everything else reads weird outputs or no outputs.


  2. Texan

    Texan New Member

    Sep 12, 2020
    180 BR
    2000 model
    3.0l w Alpha Gen 2

    No welcome to the board messages?

    No stabs in the dark on this?

    Just empty space...

    I believe the Mercarb is to blame , I reset and tested the idle mixture screw idle speed screw and checked all linkages

    The butterfly in the carb stays wide open and doesn’t seem to connect to the accelerator pump linkage

    I guess I’ll go figure this out while waiting for some sage advice here .....
  3. Dabble

    Dabble Active Member

    May 26, 2020
    Olympia, WA
    1997 330 Sundancer
    2000 230 Bow Rider
    97 - Twin 5.7 Merc V-Drives
    2000 - 5.7 Bravo III
    Changed the fuel filter(s)?

    That’s where’d I’d start.
  4. Texan

    Texan New Member

    Sep 12, 2020
    180 BR
    2000 model
    3.0l w Alpha Gen 2
    I’ll replace this week and report back ...
  5. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Just ask the questions you would like an answer to. Nice and simple without the rambling you would get a better response.
    Chris-380 and Dabble like this.
  6. hpcrank

    hpcrank Member

    Feb 4, 2016
    Col. Spgs, Co-Lake Pueblo State Park
    1981 260 Sundancer with rebuilt 454/Mercruiser330-I/O. w/ alum. hard top with front and side wdos
    One rebuilt 330 hp. 454 Chevy

    As you are mechanically capable don't hesitate to rebuild your carburetor. Go to Mikes's Carburetors on line. Besides having the rebuild kit you will need, he has free step by step videos on exactly how to rebuild your model carb.

  7. hughespat57

    hughespat57 Active Member

    Sep 25, 2016
    Rock Hill, SC
    300 Sundancer 1994, trailered tri-axle LoadRite roller
    Mercruiser 5.7 260HP Alpha One Gen II, twin
    loose wires, loose bolts, running hot, no real background on the engine, where do we start....

    Stick to the basics first
    How old is the gas? be sure its fresh.
    As suggested change the fuel filter check the lines for kinks or restrictions.
    Same for the water flow, I assume it's trailered? Running on muffs gets hot?
    Old impeller pieces can clog the feed line, hoses and the steering oil cooler (if yours has power steering)
    You may need to pull of a hose or two and be sure you have good flow.
    Do a compression test. Don't assume all is good just because it supposed to be a reman.
    You covered the timing and ignition.
    And the carb or linkages dont sound right if the butterfly "never" closes all the way.

    $2k is not much even for a 3.0, it cost me $3800 for a inline 6 Jeep ATK engine just a year ago.
    Does it say full or short block?

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