4hp 2s outboard got me stumped

[chris-s]

We acquired an early-2000’s Mariner 4hp 2stroke with our recent boat purchase. We weren’t really interested in it as we seem to have a growing collection of outboards but thought it might make a useful spare for our tender, however it is not cooperating and pretty much refuses to start. We have only managed to get it running once and that was after squirting some fuel directly into the plug hole. It ran really well for several minutes before peetering out and has not started since.

We have run thru all the usual things, fresh fuel, repeatedly stripped the carb (always been clean), fuel bowl always has fuel in it, new plug, plenty of spark, compression tested ok, replaced the fuel pump diaphragms (they looked very tired). All this and it still will not start. Squirting fuel down the carb and still no joy. I wondered about the ‘reed valve’ (or whatever it is called), it flexes, and looks like it seals ok and ‘sounds’ like it is working when pulling it over.

It seems as tho the fuel is not getting thru to the cylinder as the plug is dry.

Before I delve deeper into it, any ideas?

Chris

 

[VicS]

We acquired an early-2000’s Mariner 4hp 2stroke with our recent boat purchase. We weren’t really interested in it as we seem to have a growing collection of outboards but thought it might make a useful spare for our tender, however it is not cooperating and pretty much refuses to start. We have only managed to get it running once and that was after squirting some fuel directly into the plug hole. It ran really well for several minutes before peetering out and has not started since.

We have run thru all the usual things, fresh fuel, repeatedly stripped the carb (always been clean), fuel bowl always has fuel in it, new plug, plenty of spark, compression tested ok, replaced the fuel pump diaphragms (they looked very tired). All this and it still will not start. Squirting fuel down the carb and still no joy. I wondered about the ‘reed valve’ (or whatever it is called), it flexes, and looks like it seals ok and ‘sounds’ like it is working when pulling it over.

It seems as tho the fuel is not getting thru to the cylinder as the plug is dry.

Before I delve deeper into it, any ideas?

Chris

Symptoms suggest a more thorough carb clean needed

How good is "plenty" of spark. How far will it jump in free air ?

What is the compression in psi ?

Choke operating correctly ?

 

[snowbird30ds]

Best bet is to sell it to me very cheaply.....

 

[bignick]

I have found easy-start better for this than squirting fuel into the carb..

A few years ago I bought a 15hp Johnson that would only run for a few seconds before it cut out. I had to keep squeezing the primer bulb to keep it going. I then noticed fuel weeping out of a small crack in the fuel filter housing when I squeezed the bulb. It was just drawing air and not fuel, unless I pressurised the fuel line. I replaced the fuel filter housing, for about £10, and it ran like a dream.

 

[Refueler]

So typical of small outboards .............. gone are the days of the Seagull

I have a number of them. If not run dry to stop before storage ... carbs gum up and then extremely difficult to unblock.

I have a 4hp Mariner ... 3HP Johnson ..... 2HP Mariner in the store - all 2str - that I haven't used for some years ... I g'tee that they will not want to run ..... it will take a lot of priming / squirting / cleaning till they run sweet.
If I cannot get any to fire up after serious attempts with squirts etc. - then its off to my mate who services O/bds ..... who strips and seriously cleans everything.

 

[Pete54]

Probably dried out fuel in the carb, if the spark is 'good'. Get some carb cleaner with the tiny plastic long nozzle and carefully strip the carb down and ensure all the little passages are clear. This does take time and care. Make sure the fuel pump and working and generally that is it!

 

[Chiara’s slave]

I’ve got one that is doing the same. Mine happens to be badged Mercury, but what the hell. There’s a diaphragm fuel pump I reckon is the cause.

 

[Refueler]

I’ve got one that is doing the same. Mine happens to be badged Mercury, but what the hell. There’s a diaphragm fuel pump I reckon is the cause.

Most are based on the Tohatsu .......

 

[Chiara’s slave]

Most are based on the Tohatsu .......

They’re all pretty much clones, whoever came up with it. Good engines, just quite old now

 

[Refueler]

They’re all pretty much clones, whoever came up with it. Good engines, just quite old now

Just think ... if you offer to sell a 2str .... they do not sit around long !! Wonder why.

 

[chris-s]

Thanks for the replies.

@VicS the compression test gives a reading of 100psi which from my understanding seems acceptable. As for the ‘free air’ spark, well it arcs the plug quite happily and the choke works fine, at least from a mechanical point.

Someone mentioned that east-start, yeah we tried that as well with no luck.

We taped a latex glove over the carb throat and could see it is clearly sucking and not blowing back which suggests the ‘reed valve’ is not sticking or leaking.

If it was purely a gummed up carb, then surely fuel squirted either down the throat or even into the plug hole should show some life. In which case this would suggest no spark, but we have seen there is a spark.

Repeatedly when pulling the plug it is dry, (even after squirting fuel down the carb throat). Which I agree suggests a blocked carb. I’ll strip it again, but after having every jet, needle, cover plate and bung off of it several times already, I’m not holding my breath.

What are the cheap Chinese £40 replacement carbs like?

Chris

 

[dankilb]

What are the cheap Chinese £40 replacement carbs like?

I’ve had good experience with them - inc. one I’m running now in the very same engine. In fact, in theory if you source a 5hp carb it should have bigger jets (but otherwise be identical). That’s certainly true of the genuine Tohatsu parts - whether it’s still the case with the Chinese versions…

I’ve ordered a couple recently (got another in my 5hp Yam 4 stroke) and they turned up as they should after a couple of weeks direct from China (UK stock were more expensive).

I’ve kept the genuine carbs as backups.

 

[dac31]

If you are at your wits end one problem I had recently was that the cap on the spark plug had worked its way loose and would not spark consistently when the engine was running. If you have a new plug this is unlikely to be a problem though.

 

[Refueler]

If you are at your wits end one problem I had recently was that the cap on the spark plug had worked its way loose and would not spark consistently when the engine was running. If you have a new plug this is unlikely to be a problem though.

Given some of the crap plug connectors you see - not uncommon.

But OP did say that he's seeing a completely dry plug even after injecting fuel in carb throat ...

I had that on an old Vire ... compression was fine at TDC ... but at lower barrel - the 'slop' failed to maintain fuel to fire ... I had to seriously flood the engine to get it to even cough.

Personally given the excellent engines the OP's is when running - I'd give it to a service and accept the costs ... if its truly shot - they will say.

 

[Refueler]

The interesting item is that many of the Tohatsu based - do have same carbs in the low HP range - but have small choke / jets fitted to adjust.

Its a long time since I did it - but you could up a 4 to a 5 by small modification to the carb ... please don't ask what it was - its so long ago and I've forgotten how.

 

[Chiara’s slave]

Mine will fire up for 20 seconds after vigorous priming. I become filled with hope, only to be disappointed?

 

[Refueler]

Its also possible that someone has dismantled the engine and put it back together wrong ?? Such that spark is occurring at wrong time ?? Don't know if that's possible .... but I find it strange that he has strong spark ... reckons carbs clear ... has good suction on carb throat ...

 

[Chiara’s slave]

Its also possible that someone has dismantled the engine and put it back together wrong ?? Such that spark is occurring at wrong time ?? Don't know if that's possible .... but I find it strange that he has strong spark ... reckons carbs clear ... has good suction on carb throat ...

That would be serious butchery, IIRC it’s fixed by a woodruff key. Not to say impossible of course.

 

[Refueler]

Mine will fire up for 20 seconds after vigorous priming. I become filled with hope, only to be disappointed?

My Vire was like that !!

I sold it to a guy in Newhaven .... he stripped it ... new bearings / seals and cleaned up cylinder etc. Put it into a small workboat - lasted years !! He kept the Coil ignition from a Mini I fitted to it instead of using its Dynastart - which actually still worked.

 

[chriscallender]

I have had this happen twice with 2 stroke engines (not outboards but no different really), where they have had a clean carb, an (apparant) spark and still don't run. One time the magneto was faulty... it wasa intermittently sparking and it looked ok but didn't fire on every turn of the engine. The other time the ignition timing was completely wrong because the electronic ignition module (on a scooter) had been faulty and the replacement fired on the opposite edge (rising or falling, I don't remember) from the one it was supposed to fire on. That was a complete swine to figure out, I think I ended up spinning it over with an electric drill while looking at the timing mark on the crankshaft with a strobe then I notced that the error was exactly the width of the magnet. Only happened because the CDI thingy had been replaced with a generic one, I solved it by swapping the polarity of the pick up coil.

It could also be a broken ring/no compression, but you checked that.... so if there are sparks they are either weak/intermittent or at the wrong tinming.