Mariner 2.5 reluctant to start

[jsl]

Having been very well-behaved for years, our little outboard has developed a grumpiness. Advice would be welcome.
Full throttle and choke may produce a start, but re-starting is very difficult. Plug is new, fuel reaches carb easily, carb is clean, fuel is not very old - but the symptoms suggest (to my ignorant mind) fuel starvation. It will sometimes start, run for a moment, then die. I have a feeling that when running (which it does sometimes) it is not reaching full revs, and tends to decline gently after a few minutes at full throttle.
I've found an exploded diagram on this forum, but not a parts list, which makes it difficult for me to decide whether I could achieve anything by further dismantling. What is the name of the screw (with spring) on the side of the intake body opposite the fuel pipe connection?

 

[jwilson]

If a two-stroke the screw is idle setting, just restricts full lowering of throttle slide. Sounds like a carb jet or needle cleanliness problem: on these little two-strokes there is only the one jet.

 

[VicS]

Having been very well-behaved for years, our little outboard has developed a grumpiness. Advice would be welcome.
Full throttle and choke may produce a start, but re-starting is very difficult. Plug is new, fuel reaches carb easily, carb is clean, fuel is not very old - but the symptoms suggest (to my ignorant mind) fuel starvation. It will sometimes start, run for a moment, then die. I have a feeling that when running (which it does sometimes) it is not reaching full revs, and tends to decline gently after a few minutes at full throttle.
I've found an exploded diagram on this forum, but not a parts list, which makes it difficult for me to decide whether I could achieve anything by further dismantling. What is the name of the screw (with spring) on the side of the intake body opposite the fuel pipe connection?

Parts lists and diagrams at boats.net
But all shown in service manual at http://boatinfo.no/lib/mercury/manuals/22-25-3-33.html#/0

Clean the carb again , check spark with spark tester. Check compression.

Screw is idle speed

Give it fuel that is not old at all.

 

[jsl]

Very useful advice: many thanks. I'll get to work with the spanners.

 

[Bobc]

The float jets chorode and start sticking. Often that results in either the engine flooding, or more usually the float chamber not filling properly resulting in the engine dying.

I would suggest getting a new one, but as a temporary step, you can give the current one a light rub down with some wet & dry.

 

[jsl]

Well, I've cleaned the carb as best I can. (When I first said it was clean, I was referring only to the bowl.) Found a tiny bit of Verdigris (?) on the needle, but otherwise all was as bright as bright. And lo and behold: starting now seems to be reliable and predictable. Bingo!
There is still some reluctance to run slowly, but this is hard to judge when running in a bucket.
Presumably it's not a bad idea to give a dose of carb cleaner every year or so: I imagine squirting through the air intake, as recommended on my shiny new tin of cleaner, but also perhaps through the fuel intake.
Many thanks again.

 

[tjanna]

If you haven't done so already, I would remove the fuel tap assembly completely and check the tube that pokes into the tank, it has an in built gauze filter, when it becomes clogged from debris in the tank it can cause intermittent fuel starvation.

G

 

[jsl]

Yup: I've checked the tiny filter. Had problems there some years ago, so I'm conscious of that one.

 

[Flica]

If you haven't done so already, I would remove the fuel tap assembly completely and check the tube that pokes into the tank, it has an in built gauze filter, when it becomes clogged from debris in the tank it can cause intermittent fuel starvation.

G

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