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Old 24 February 2014, 12:17   #1
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75HP 2 stroke Mariner

I've got a 75HP 2 stroke mariner outboard on my RIB. It's a great engine, runs very well and pushes the boat along fine. It's just it's never very easy to start, but the problems it creates are sort of inconsistent.

Our starting routine is as follows;
1. Plug in fuel, vent tank, pump bulb until firm.
2. Ensure engine is trimmed completely down.
3. Lift fast idle lever
4. Turn key whilst pushing inwards (choke), release when engine starts/after a few seconds (try again if it doesn't)

When it hasn't been used for a while, it takes at least 5 minutes of this to get it going, and once it is actually going I won't leave the mooring for another 5 minutes to check that it's not going to cut out (as it has done whilst launching from a lee shore on my own...). Generally though, once it's going it will perform with absolutely no issues.

Under regular use, it's very hit and miss. Sometimes it'll go straight away, other times it'll take lots of encouragement and even then it won't go easily. You could start the engine instantly, go for 10 minutes, stop it, try and start it again and have to try 10 times before it actually wants to work again.

The engine is serviced and winterised at the end of each season, it's kept indoors over the winter months and it's used reasonably regularly in the summer (kept on a swinging mooring).

Has anyone got any tips to make it easier, or perhaps any ideas as to why it's so unpredictable?
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Old 24 February 2014, 12:19   #2
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Why do you lift the fast idle leaver?
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Old 24 February 2014, 12:24   #3
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Yep, no need for fast idle


When mine start if it sounds like they are going to cut out I just give the key another little press for choke and that sorts it.

Never really seen the need for fast idle.... At all.
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Old 24 February 2014, 12:26   #4
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Fast idle lever seems to be the best way to make it go, experience has shown that it doesn't tend to start without it. is that bad? Some people I know have recommended that we always do it like that?
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Old 24 February 2014, 12:33   #5
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Quote:
Originally Posted by bad_moose View Post
Fast idle lever seems to be the best way to make it go, experience has shown that it doesn't tend to start without it. is that bad? Some people I know have recommended that we always do it like that?
That would suggest that it needs attention, there are three circuits in a carb, idle, intermediate and main jet.

So if it works flat out but doesn't idle/start well then may be the idle circuit needs a clean or adjustment.

You may benefit from an ultrasonic carb clean? If you can prove that this is the problem.
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Old 24 February 2014, 12:34   #6
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Quote:
Originally Posted by bad_moose View Post
Fast idle lever seems to be the best way to make it go, experience has shown that it doesn't tend to start without it. is that bad? Some people I know have recommended that we always do it like that?
I suppose it depends on the engine as some engines use a fuel enricher as a choke meaning it dumps extra fuel in for choke, some engines use the Venturi butterfly to reduce air thus making the start mix richer.

It may be that you are dumping too much fuel in for it to start easily.

How are your plugs? Are they the correct ones for the engine?
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Old 24 February 2014, 12:39   #7
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Quote:
Originally Posted by whisper View Post
That would suggest that it needs attention, there are three circuits in a carb, idle, intermediate and main jet.

So if it works flat out but doesn't idle/start well then may be the idle circuit needs a clean or adjustment.

You may benefit from an ultrasonic carb clean? If you can prove that this is the problem.
Is that not something that would come up when the engine is serviced? The place we take it to has a good reputation, all the local boats go there for any work that their engines need, including a fair few local businesses.

Quote:
Originally Posted by A1an View Post
I suppose it depends on the engine as some engines use a fuel enricher as a choke meaning it dumps extra fuel in for choke, some engines use the Venturi butterfly to reduce air thus making the start mix richer.

It may be that you are dumping too much fuel in for it to start easily.

How are your plugs? Are they the correct ones for the engine?
Mm we did think that may be the case initially, but pumping less fuel in with the bulb doesn't seem to make much difference. I think that all this inconsistency is what is making it hard to pin down...
I'm not sure at the moment, the plugs were changed when the engine was serviced a little while ago and I haven't looked since. As I said though, the engine has been looked after by a reputable company who have lots of customers, I'd trust them to use the right parts for the job. I'm going to the boat on the weekend and I'll check it out though.
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Old 24 February 2014, 12:47   #8
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Like whisper says, a carb clean may be in order.

Always prime your carbs until bulb goes solid.


9 times out of 10 starting problems with outboards come down to fuelling whether its dirty carbs or dirty fuel.

I don't know why though. I've got a couple of Husky chainsaws that work hard as hell and NEVER need their carbs stripped, the fuel cans are caked in years of saw chippings and chain oil but yet the engines never give any bother, same goes for the strimmer, you can hardly see the carb for dirt and dust yet it never misses a beat.

You let one little bit of shit into your boats fuel can and itl magically make its way through all the filters and jam itself in a carb jet at the most awkward of times.
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Old 24 February 2014, 13:21   #9
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right i pulled my hair out with mine - same trouble as you. this is what i did (im not suggesting this is the answer, just what worked for me).
cutting a long winded story short, i opened upthe idle screws on the carbs quarter/half a turn, and advanced the ignition timing - transformed the starting. in the process of trouble shooting i figured that the enrichener while it was working wasnt getting much extra fuel into the engine, and i realised that if i pushed the choke at the same time as squeezing the primer it would force fuel in and so meant i could start from cold no worries.
does your engine die if idling for too long? mine used to, until i did the carb and timing adjustment.
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Old 26 February 2014, 12:21   #10
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Okay guys, thanks very much! I'll have a look at the carbs and see about getting them cleaned up if they need it, and if that doesn't sort the problem then I'll look into the idle screws on the carbs and the ignition timing too. Cheers!
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Old 26 February 2014, 15:08   #11
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Don't forget to choke the engine. On Merc/Mariners this is done by pushing the key up into the throttle box.

If you do this you may find it helps it start. However a service, particularly cleaning plugs will help.

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Old 26 February 2014, 15:28   #12
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I agree as a Mariner 2 st owner with all the pointers from the guys as I have had similar issues. One thing I have learned is that it's fast idle or choke you may catch the engine after using choke but they cancel each other out!!
One other thing check you battery leads and connections all the way from bat to engine also check starter solenoid. Hope this helps. Since I renewed my bat cables and starter I've been a lot better.

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Old 26 February 2014, 15:51   #13
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I would also check that the choke is getting fully closed by the choke solenoid. This happened to me once, we spent hours in the early days, engine would not start. Changed plugs, checked everything

Did some fine checking and found that the choke flaps were not quite fully closed, used the manual override and the engine started immediately, finally but a kink in the fine lever to the chokes (to take up the slack) and the engine never missed a beat.

Just have a quick check and make sure the chokes are fully closed when the key is pressed in. You shouldn't be able to move them any further
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Old 26 February 2014, 16:26   #14
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the cold start isnt a traditional choke mechanism, it is an enrichener which dribbles fuel into the crankcase
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Old 26 February 2014, 17:58   #15
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Hi
You could try taking the plugs out and look at the colour: -
white or light grey - running lean
Chocolate - correct mixture
Black - too rich
This could give you an indication which carb may have a dirty jet.
Hope it helps
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Old 27 February 2014, 03:22   #16
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This is what i would do if it was mine or a customers OBM.
1/look at the colour of the tip on the spark plugs, make sure that they are the correct s/plugs, and properly gapped.
2/I would remove the carbs, strip examine and clean, re-assemble as per factory spec.
3/when it was running make sure the timming was within the factory spec.
4/ synchronize the carbs.Dont tuck the obm right under have it straight up and dowm.
when it is tucked under it is running in arich condition
5/to sync the carbs, with the obm ticking over the screws that hold the rod that operates the throttle slacken so the engine sucks the butterflys shut then carefully re-tighten screws.
I would set all the carb idle mixture screws at one and a half out from lightly seated, and dont forget to check the oil pump lever is in the correct position.
Obviusly check compressions
On the coast guard obms that I used to service I fitted a transit bolt across the the transom brks so the leg couldnt be tucked right under.
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Old 27 February 2014, 07:59   #17
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when you have done the above, you should have roughly about a 200rpm rev change from nuetral to in fwd gear, then you know you are as near to spot as you will probaly get. Like most things its easier to do than write about.
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Old 27 February 2014, 16:54   #18
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That told me

Quote:
Originally Posted by Festinghouse View Post
the cold start isnt a traditional choke mechanism, it is an enrichener which dribbles fuel into the crankcase
Sorry guys, thought it was a choke flap operation, didn't want to confuse.

Best of luck with your investigation
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