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Hi folks,

 

I doubt this can be diagnosed by video but I have one any way!

Fired the boat up for the first time in a couple of weeks and it's started stalling at low revs and very much when you stick it in neutral.

 

I checked the spark plugs to ensure the seemed connected but this pretty much exhausts my knowledge at this point..

https://photos.app.goo.gl/iirBFMn7fti5YPD1A

It's supposed to be getting serviced in a few weeks so I'll probably have to wait until then but worth an ask!

 

Thanks

 

Tom

 

 

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Thanks @Turnoar, I did get in the water and have a feel around today but didn't find anything. That said, if its in neutral, the prop isn't spinning is it so it shouldn't affect its stall-ability? In gear I could understand it.

 

Thanks @grendel, this is where it gets beyond my limited knowledge, I'll get the service guys to look at it and hopefully they can give me some tips for next time :)

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Could be the idle speed sensor, on some younger model engines they use sensors that regulate the engine revs, which means you cant just turn an idle screw to regulate the tickover speed. If you have the Mercruiser  model number it may be possible to get some information to help you. Should be called a throttle position sensor I think.

Paul

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Thanks @scaniaman

I did have a scan through the manual this afternoon but didn't find anything about adjusting the idle RPM and as you barely get a signal at St Olaves gave up trying to Google it. I will dig out the model number tomorrow, forgot to make a note of it today.

That said, as it was working find on each test run we had with the boat and until a week or so ago, I had wondered if I could find a way to adjust the idle RPMs but it also felt like it was probably a fudge as opposed to a fix as it has gone from fine, to not great, to just flat out stalling on a warm engine in 2 cruises.

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Yeah I wondered about fuel, old fuel etc, when we bought it it was basically empty so NYA stuck 40L of fresh fuel in it and I've filled it up a bunch of times and its currently got 70ish Litres in it, so I don't think it should get too sad on 1/4 tank. But yeah fuel supply had crossed my mind.

 

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Hi check around carb and look at all the little hose connections they often perish and let air into carb giving it a lower fuel mixture at slow tick over engine speeds it is not noticeable at higher higher speeds if all ok, remove air hose on top of carb rev engine up at the same time place your hand NO RAG over the carb inlet at the same time flip the throttle open to increase vacuum and flush petrol through jets,  as engine stalls/slow down remove your hand before it stalls and gently rev the engine up this will hopefully suck/clean the residue from the jets that accumulate from petrol when it drys out you should always turn the fuel off and run the engine dry when leaving it for any length of time, if you have a diaphragm fitted it could have a pin hole in it through pershing, which will need replacing, couldn't see what carbs you have but petrol leaves a shellac stain on brass when it drys out and the jets are made of brass. if this doesn't work you will need a engineer to check it over. if you have two engines it is good policy to only run one at a time as they often don't get run fast enough on the broads due to speed restrictions.John

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Thanks for the hints, tips and advice folks, @scaniaman's tip wins! :). I went back through the manual today and found the idle RPM screw and gave it a tweak which solved the issue for now. I also got a pretty detailed explanation from Peter at Northgate Marine who explained the whole transmission, ignition setup and explained how this is a reasonably common problem especially for sticky cables.

Anyway! Back up and running for now and its going to get serviced soon anyway, so I'll get them to clean it up and get it running well again in a few weeks.

Tom

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Hi Tom As you have just bought it i would check the fuel tank for water that collects in the bottom from condensation, more so on petrol as people don't tend to keep petrol fuel tanks full over winter unlike diesel. petrol tanks don't have a drain of tap to purge water from bottom of tank like diesel one's do, weight/tip the boat over to the fuel filler side leave for a while then with a 1/4 inch length of hose insert to lowest corner of tank through filler and suck/pump out into clear container you will see the difference between petrol and water, you my well find that the bottom of tank has water in it this is from condensation that accumulates over time, and when it gets high enough to reach the fuel outlet pipe level then collects in bottom of carburetor bowls affecting the slow speed running fuel mixture. John

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Mercrusier 5.7 by the looks of it. Basically a marinized small block Chevy. Check the auto choke is not sticking, also they don’t like running cold, does it idle once its warmed up? There should be a water separating fuel filter in the fuel line, worth a check, just take it off an pour the contents into a glass jar and let it settle out, any water will sit on the bottom. Other than that could be a blockage in the idle circuit in the carb, they are not too complicated to strip and clean blow the jets out with a can of carb cleaner. Once warm it should idle about 650-700 rpm. If it is stalling going into gear there is an interrupter micro switch on the gear shifter, this intentionally stalls the engine for a fraction of a second while going in to gear, may need adjusting. After all that I guess it probably an electric fuel pump, so check the connections for any corrosion. (been there done that :D)

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