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  1. #1

    Default 260 Mercruiser w/ TB IV Shutting down on load, at temp

    1986 Wellcraft 23 Nova XL, Alpha One. 260 Mercruiser (350 Chevy) Bone stock

    First time this has ever happened - On holeshot start, when getting on plane, RPMS drop down to zero. Engine shuts off and is acting like no spark. Carb is squirting fuel, can smell that it is getting fuel down the carb.

    Let it cool some, and it starts up, and gets on plane like it always has since I have had it - years...

    Couple things:

    -- Last year, since the last couple years have not used it much - felt the fuel may be getting old. Had it out and it was acting like a lean backfire on full throttle. Could it be the octane was getting low I thought... So I pulled the sending unit and set up a siphon and drained the tank. Ran the boat till the fuel in the carb would not fire it and put it away. This year, put 20 gallons of fresh fuel, and it ran fine for the the first part of the day. No backfires, ran strong just like it always has.

    -- Always winterize it.

    -- After this shutoff situation, yanked the carb and have cleaned it up and checked it out as part of the rebuilding (cleaned it last night, will put it back together tomorrow) Figured it was due anyway. Looked better inside than I expected. Some sediment, but not bad. It looked like the float was shutting off the fuel o.k.

    -- I am thinking that it could be the Thunderbolt IV shutting off. Thinking about putting in a Pertronix on it after confirming my distrubutor number with Pertronix (They show it as a Mallory in their catalog, but a friend of mine and I think it is a Merc distributor)...

    -- Normally the pickup in the distributor is either it works, or it totally leaves you stranding, right? I figure even if it is bad, I'd throw a Pertronix in anyway.

    Any suggestions and personal experiences are appreciated.

  2. #2
    Moderator Bondo's Avatar
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    Default Re: 260 Mercruiser w/ TB IV Shutting down on load, at temp

    -- I am thinking that it could be the Thunderbolt IV shutting off. Thinking about putting in a Pertronix on it after confirming my distrubutor number with Pertronix (They show it as a Mallory in their catalog, but a friend of mine and I think it is a Merc distributor)...

    -- Normally the pickup in the distributor is either it works, or it totally leaves you stranding, right? I figure even if it is bad, I'd throw a Pertronix in anyway.
    Ayuh,.....

    Pertronix is for converting a Points distrubiter,... Not Fixing a T-Bolt IV,....

    You'll do Better by repairing the T-Bolt.....

    Go Here,+ you can download the Manual for your driveline,....
    Then just go through the diagnostic tree to see just What's going Bad.....
    Any Grease is Better,..... Than No Grease at All.......

  3. #3
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: 260 Mercruiser w/ TB IV Shutting down on load, at temp

    Get your tools handy, and the next time it stops and won't start, do these tests.

    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
    Only forum/moderator issues will be answered in PM's.

  4. #4

    Default Re: 260 Mercruiser w/ TB IV Shutting down on load, at temp

    Thanks for the inputs above. I'm the type that does like to troubleshoot down to the exact problem before shotgunning, so please don't get me wrong. Rebuilt everything from alternators, ps pumps, engines, etc. etc. over the years.

    Even when my buddy that has probably 50+ years experience building, racing, and working on Mercruiser and other brands was telling me about the problems he has seen - I still wanted to get to what the problem is.

    Reason for converting to the Pertronix (if it is the box or the sensor/pickup in the distributor) is cost, simplicity and perhaps dependability. I have seen performance improvement in the past with automotive conversions.

    Will check out the manual, fault tree and test points in the boat before going out with tools. My big thing is that I don't want to get stuck out on the river and get towed in or anything like that. Never have, and don't want to now.

  5. #5
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    Default Re: 260 Mercruiser w/ TB IV Shutting down on load, at temp

    Believe me never been towed till this week. No fun at all. Read my last thread.

    Your problem will be discovered with dons tree he posted. One question when was the last time you checked the risers?

    I asked for a reason. Friend had a problem just like yours. Smae motor as yours. He wouldn't listen to me.

    Brought over the chain hoist for my motor to use to pull it out. Told me he finally checked the risers. One was plugged solid.

    He was to red faced to call me.

  6. #6

    Default Re: 260 Mercruiser w/ TB IV Shutting down on load, at temp

    Quote Originally Posted by chiefalen View Post
    One question when was the last time you checked the risers?
    Exhaust manifolds and risers were changed a couple years ago. Had a slight exhaust leak and went ahead and put new back in before problems arised. Not too many hours on them since then and I always run the engine with the ears after a day out.

    I can hear my flappers flapping at idle, so I think they are o.k. as well - will confirm them when I get the carb on. Carb is back together, painted. Was busy with a few car projects and home projects this weekend - so I did not get a chance to put the carb on and pull the boat out of the garage to fire it up.

    Thanks for the tip - yep the risers can get pretty clogged.

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