Merc 90 2S query

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    Posted: 23 Apr 2022 at 1:04pm
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So I do all my own maintenance and have done for decades. Problem solved everything to date.
This one has me stumped right now.
The motor has a bad habit on first startup of the day of dying under throttle for the first power up.
It will either drop a cylinder and run flat out at a max of around 3500rpm, (just up on the plane) until the 3rd cylinder kicks in and it takes off like a rocket. Or it will stumble and die completely. At which point it starts right up and may stumble again, or may power up. As soon as it powers up on all 3 with no stumble, it is perfect all day. Can sit at anchor 3-4 hrs, fires up and powers up straight away. It will only do this first time each day.
I have stripped the carbs - clean as, re set one float level (slightly out). Checked fuel supply (but makes no sense - runs good all day), checked filters, checked for air bubbles in the line. New plugs, even bought a new coil and swapped that around. One carb seems not to tune quite so well on idle mix. Thats the worst culprit/symptom I can find. Cannot find any obvious issue with it. Have checked the timing. Checked everything I can think of. Replaced the thermostat for a warmer one - the shop suggests they run better at higher temp than factory spec.
I can idle the motor for 5 minutes and it will still die on first throttle boost. Then clears and good to go.
I have run out of possibilities.
Alan
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Post Options Post Options   Likes (0) Likes(0)   Quote Kandrew Quote  Post ReplyReply Direct Link To This Post Posted: 23 Apr 2022 at 2:48pm
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This might sound odd, but I would take the fuel pump diapharm out and give it a good check over for any small holes, diapharm should be replaced regularly on the ELPO 90.
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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 23 Apr 2022 at 3:00pm
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I have always done my own servicing too. I'm very familiar with two stroke motors. My first thought is that at least one ofr the cylinders is running lean. When you say you've checked the float levels you clearly know some stuff. Are you sure one of the floats isn't sticking on the side of the bowl? It sounds much more like a fuel/air mixture issue than anything else.

Does it run better on ear muffs than in the water?

Are the carbs synchronised?

It sounds like it's lean to me, that's why it is ok once underway. Fuel starvation is similar to an air leak in a way. The issue may even be something like a crankcase leak Ouch due to worn crank seals etc.

What is the motor? I can't quite figure it out from your post. I'm guessing a 3 cylinder Mercury 90hp? How old and how many hours? I'm not a mechanic but I have a little 2 stroke nous :)
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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 23 Apr 2022 at 3:02pm
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As I was posting this Kandrew posted up about the diaphragm, makes a lot of sense and well worth checking out
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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 23 Apr 2022 at 3:58pm
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Yeah - forgot - have replaced the fuel pump bits too. New diaphragm. Also checked compression - perfect.
Agree Smudge - feels like a lean setting - but the main jet mix is fixed. Only the idle can change. At the moment I have set them slightly on the rich side - thinking same as you. Also, depressing the 'choke' button, when under power and hesitating, does not improve it. That fires a shot of fuel direct in to the carbs.
Yes - carbs synchronised - as best I can see - bottom carb hard to check as well as the top 2. But nothing obviously out of kilter. Not sure how critical that is - thousands of an inch? Visibly they look the same at fractional opening - eg 1mm gap. Seems even on all 3. Yes - 3 cyl Merc 90.
Hrs - dunno. Boat has an hr meter - but motor was not original to boat as far as I can tell. At some point this motor - which I suspect already had hrs on it, was fitted to the boat. It is a S African motor originally. Someone has brought it over with them, then fitted it to this boat.
but it runs fine and has done for the previous 10 yrs, other than this annoying issue.
Regards
Alan
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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 23 Apr 2022 at 4:03pm
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Just thinking on - one thing I should check is that the float needle valves are sealing properly. If not, the carbs could be over full at start up - prime the bulb. Maybe too much fuel in a bowl, which corrects itself once up and running. Not sure if I have checked that or not. I should check the synchronising again and check fuel is not spilling out into the carbs  on priming.
Apart from the pain of dragging the boat in to town on a trailer without a WoF, the shop will basically get one shot at trying to identify the problem each day - cold startup. And they will have to run it in the tank to see the problem.
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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 23 Apr 2022 at 4:17pm
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Checking the needle valves goes hand in hand with checking the float heights. The important thing is where they shut off. Synching the carbs, well the only way to do it properly is with vacuum gauges but outboard motors are a relatively low state of tune. The carbs should all look identical at idle and all start to open at the same time. Problem when cold - air leak/lean. The air leak would have to be post butterfly on the intake side if that makes sense?
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Post Options Post Options   Likes (0) Likes(0)   Quote Pcj Quote  Post ReplyReply Direct Link To This Post Posted: 23 Apr 2022 at 4:48pm
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There lies a possible problem,as Smudge just mentioned butterflies,are all 3 opening and closing sametime,you say once warm runs fine,had a issue once as spring was worn on a 3 cylinder marina 50hp,fine warm but cold hard going,mechanic found worn spring as fly not opening/closing compared to other 2
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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 23 Apr 2022 at 4:57pm
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Right  then I need to sort a vacuum gauge, and check this - I know the thing you mean. Could be the telling info I am missing. Used for synchronising carbs like strombergs/SUs etc. Not sure I have one - but will sort something. Maybe buy one.
Air leaks - yep another possibility.
Check springs and butterflies again. Sounds on right track. makes sense.
Thanks guys. I want to nail this - very frustrating - esp beach launching. Adds another dimension I can def do without.
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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 23 Apr 2022 at 5:01pm
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If the throttle shafts are worn as in there is obvious movement in them, that would be a problem. Vacuum gauges aren't cheap, I'd explore all other options first or ask an outboard mechanic Wacko for advice . There are some good ones and they know more than you or I.
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Post Options Post Options   Likes (0) Likes(0)   Quote Kandrew Quote  Post ReplyReply Direct Link To This Post Posted: 23 Apr 2022 at 5:17pm
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How many hours has it done, sorry just read above you don’t know the hours. Generally a fuel issue won’t be intermittent it will be there all the time. When you first fire it up have you pulled a plug lead to see which cylinders it’s running on. You can use a timing light to see if there’s anything coming down the wire. I used to have a spark plug with a jumper lead lead clip welded on the side so I could clip it onto the engine block then when the engine starts playing up I could stop the engine, plug the lead onto that plug and check the condition of the spark, which should be nice and blue. What do the plugs look like, all burning nice and clean and gapped right.

Fuel system on these engines are pretty bulletproof but the diapharm give a lot of problems that’s why I always go there first. Coils and the trigger can give this type of issue so this is where a marine shop can start to swap parts. Remember engines run much better once warmed up so slightly weak coils will only show up when the engine is cold.
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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 23 Apr 2022 at 6:35pm
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Thats why I got a new coil - and swapped it over between the three. No change.
But I will get my timing light and check the cylinders again. I tried pulling plug leads - and got a massive whack every time - not to be repeated. Even with rubber handled pliers and rubber gloves. My timing light is a more user friendly approach.
Gapless plugs.
I have a carb vacuum gauge on order - will take a few weeks - UK.
I have a shed full of tools. What I save on labour I am happy to invest in tools.
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Post Options Post Options   Likes (0) Likes(0)   Quote Kandrew Quote  Post ReplyReply Direct Link To This Post Posted: 23 Apr 2022 at 7:09pm
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Yes you need a proper set of spark plug pliers for outbourds, mine are all plastic know steel. Didn’t read you had replaced the coil, might need to try a ignition module next but you don’t want to keep buying parts.
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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 23 Apr 2022 at 7:46pm
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I think I def need to be hunting around the carbs,air leaks right now until dead certain. Will also get my timing light and check the ignition to each cylinder.
I need some plastic pliers - I am gun shy of those leads now. Where do you buy those?
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Post Options Post Options   Likes (0) Likes(0)   Quote Kandrew Quote  Post ReplyReply Direct Link To This Post Posted: 23 Apr 2022 at 8:00pm
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Originally posted by Alan L Alan L wrote:

I think I def need to be hunting around the carbs,air leaks right now until dead certain. Will also get my timing light and check the ignition to each cylinder.
I need some plastic pliers - I am gun shy of those leads now. Where do you buy those?
Alan
Got mine many years ago but these might be ok.

https://www.tridon.co.nz/products/Toledo/24048/327594/fencing-pliers/409554/spark-plug-lead-and-boot-pliers/428205/302161

These look more like mine, but look for a pair of none conductive pliers

https://www.clydesdale.net/clydesdale-products/tools/product/universal-composite-pliers

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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 24 Apr 2022 at 7:43am
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Excellent - never seen them before. I am on to it.
2 new tools on the way. Vac gauge and plastic pliers.
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Post Options Post Options   Likes (0) Likes(0)   Quote bazza Quote  Post ReplyReply Direct Link To This Post Posted: 24 Apr 2022 at 1:52pm
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Alan mate ... the cause of the problem is obvious & often encountered with motors that have been used in Sth Africa.

You are almost certain to find your water impeller is chocka full of croc & hippo excrement which clogs up the coolant when cold but becomes supple as it warms up.

There you go .... should have asked an expert in the first place!
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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 24 Apr 2022 at 2:17pm
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Sorry Bazza - never occurred to me. Duuh.
It actually may be right now. Spent some time on it this morning - after Smudge's and KAndrews comments.
Reset the carb tuning, and corrected what looked like a very small unsynch issue. Did not falter this morning and seems to be idling better.
Will know better tomorrow when I brave the surf for my cray pots.
5 snaps today - but slow going and 4 are pannies. But nic day on the water.
KAndrew - I have found a new way of getting the HT leads off - claw hammer, and gardening glove.
Not a hint of a zap perfect.
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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 24 Apr 2022 at 4:48pm
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I wouldn't be surprised if that changes on the water but I hope it is all good now Alan
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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 24 Apr 2022 at 5:54pm
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Yes - agree. But was good on water today. Had power when I needed it. Boat breaking surf right now if you time it wrong. 2-3m. But had spent some time on the muffs an hr or so prior to leaving. Will see tomorrow.
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