Engine seems to start but rolls to a stop

[GrowleyMonster]

Heat gun or powerful blow dryer. Get hot air into those cylinders. Cover air filter with a rag, spritz some WD40 on it. Much more gentle on the engine than straight ether based starting fluid. Don't spray directly in the intake. That sends compression through the roof, and maybe the head or a valve, too. Usually hot air alone will do the trick.

Get yourself a spare or better yet two spare valve cover gaskets. Pull the valve cover and roll the engine over by hand and watch for proper valve operation. Set the lash according to the manual. Probably not the problem and probably won't indicate a problem but it might, and likely your valves could use adjusting, anyway.

Next thing I would recommend is a compression test. That will tell you a lot about your engine. Does it smoke? Excessive smoke usually indicates worn rings or cylinder liner walls.

Injectors... did you pull the injectors, or just bleed the lines? Pull an injector and aim it at a piece of cardboard, and observe the spray pattern, if there is one. Wear eye protection and be careful, that fuel is under very high pressure. If there is no spray pattern but you have plenty fuel to the pump, then you have isolated the problem somewhat. Try new injectors. No joy? Then read on.

Even if you were successful at bleeding the injector lines, your secondary (engine mounted) fuel filter could be clogged and restricting fuel flow to the high pressure pump.

Probably not a solenoid but make sure that there isn't a low oil pressure switch that sends a signal to close the solenoid operated fuel valve, if you have one.

Throttle linkage. For troubleshooting, operate the throttle right there on the engine, not with the Morse controls at the helm station. You want the throttle opened up a bit. Try about 1/3, then 1/2 but be ready to trim it back when/if it starts.

During all this fooling around, definitely keep the seacock closed, but remember to open it if you get a good start. It is easy to forget that, when you are doing the happy dance.

Timing chain or gears could be worn. Starting to get out of the DIY range here, calls for mechanic.

High pressure, i.e. injector, pump, or the governor. This is the most involved fix, the most expensive, but sadly I fear the most likely problem. Make sure you have good flow to the injector pump, first. Check that your have fuel returning to the tank. No return fuel indicates a problem. No return fuel but good flow and lift pressure to the injector pump nails it, and you know it is the pump or governor.

Just for the hell of it, check your primary filter that it is full to the brim with fuel. If you have a clear bowl type primary filter, check for water and dirt. Install an electric lift pump right at the tank or tank manifold, or a squeezey bulb. Pump with the primary filter bleed screw loose until fuel overflows, then tighten. work down the line. Bleed the secondary, and tighten good but be careful not to break anything. Loosen the connection to the injector pump inlet, bleed there. Then go for start with injector lines cracked, to bleed them, tighten when you see fuel. Systematic, step by step, right down the line. Sometimes it is the simple stuff, and we overlook it or do it halfassed because it is the simple stuff.

[SY Harmony]

In the US, WD40 changed about 10 years ago and isn’t the starting fluid it use to be. I believe they removed propane as the propellant.

[GrowleyMonster]

Originally Posted by SY Harmony

In the US, WD40 changed about 10 years ago and isn’t the starting fluid it use to be. I believe they removed propane as the propellant.

Shuckey darn. I just KNOW I used some to start a neighbor's stubborn and cold blooded 4-108 a couple years ago, but it might have been an old can. It worked pretty good and didn't clatter the valves the way ether sometimes does.

[JustinT]

Thanks sooo much for this. I'll get to the boat and give it all a go.

[Wotname]

Originally Posted by SY Harmony

In the US, WD40 changed about 10 years ago and isn’t the starting fluid it use to be. I believe they removed propane as the propellant.

Originally Posted by GrowleyMonster

Shuckey darn. I just KNOW I used some to start a neighbor's stubborn and cold blooded 4-108 a couple years ago, but it might have been an old can. It worked pretty good and didn't clatter the valves the way ether sometimes does.

In a pinch, an alternate bush mechanic's approach is to use 90/10 mix of diesel/petrol (gasoline) in a spritz bottle. It is best to try 100% diesel first but add up to 10% petrol if the situation demands it. Mist the fuel lightly into the air intake or soak a rag and hold it over the air intake.

Obviously much care has to be taken when misting a petrol mix around in an engine bay.

[JustinT]

Well, I tried the above on high tide tonight.
It really seems to be running but as soon as I let go of the key the engine slowly stops, so very slowly.
There is fuel going back to the tank.
The injectors are spraying. However, I loosen one and it makes no difference. I loosen the other and it's very sick.
Also, on first turning the key it sounds super sick but then rapidly cranks to what is sounding like a running engine. Let go of the key... putt putt putt putt putt stop

I assume I must not keep cranking&cranking and destroying the starter motor?

[skipperpete]

Originally Posted by JustinT

Well, I tried the above on high tide tonight.
It really seems to be running but as soon as I let go of the key the engine slowly stops, so very slowly.
There is fuel going back to the tank.
The injectors are spraying. However, I loosen one and it makes no difference. I loosen the other and it's very sick.
Also, on first turning the key it sounds super sick but then rapidly cranks to what is sounding like a running engine. Let go of the key... putt putt putt putt putt stop

I assume I must not keep cranking&cranking and destroying the starter motor?

You assume correctly. Also, keep the raw water intake closed until it runs unassisted. Have you tried starting it at full throttle (in neutral of course), that might help.

[JustinT]

Originally Posted by skipperpete

You assume correctly. Also, keep the raw water intake closed until it runs unassisted. Have you tried starting it at full throttle (in neutral of course), that might help.

I've tried all throttle positions. Mostly I've tried it with no water and the impeller removed.

[JoeRobertJr]

Originally Posted by JustinT

The injectors are spraying. However, I loosen one and it makes no difference. I loosen the other and it's very sick.

This seems like an important clue, though I don't what to conclude from it.

[Wotname]

Originally Posted by JustinT

Well, I tried the above on high tide tonight.
It really seems to be running but as soon as I let go of the key the engine slowly stops, so very slowly.
There is fuel going back to the tank.
The injectors are spraying. However, I loosen one and it makes no difference. I loosen the other and it's very sick.
Also, on first turning the key it sounds super sick but then rapidly cranks to what is sounding like a running engine. Let go of the key... putt putt putt putt putt stop

I assume I must not keep cranking&cranking and destroying the starter motor?

I suggest it is not firing on the cylinder marked in red and it is firing on the one marked in green.

This means the sick cylinder either does not have enough compression to start when cold or is not getting any fuel via the injector.

Given the other information upthread, my best guess is the lack of compression. Perhaps broken rings or piston lands from the run away event you described earlier.

[JustinT]

Originally Posted by Wotname

I suggest it is not firing on the cylinder marked in red and it is firing on the one marked in green.

This means the sick cylinder either does not have enough compression to start when cold or is not getting any fuel via the injector.

Given the other information upthread, my best guess is the lack of compression. Perhaps broken rings or piston lands from the run away event you described earlier.

Ah, thank you, we seem to be drilling down to the problem now.

[GrowleyMonster]

Sounds like time for a compression test. Or segue right into a teardown. Rings, or valves. I would bet money it is one or the other on the cylinder that doesn't seem to be doing anything.

[JustinT]

Humm, when the engine did work it wasn't all that powerful. Max 6 knots.

[JustinT]

Success! It was the injector. Fiddled with the fittings again and tried the compression, both levers were fixed together but I made them independent and that worked. I turned the engine with the wonky one compressed and the other normal. As it turned I flicked the lever on the wonky one and the engine ran. Was no impeller or cooling so I didn't run for long. Will go have a fiddle on the super high tide tonight when I have cooling.
Thanks to all on this thread and the problem solving. Couldn't have done it without you!

[GrowleyMonster]

Originally Posted by JustinT

Success! It was the injector. Fiddled with the fittings again and tried the compression, both levers were fixed together but I made them independent and that worked. I turned the engine with the wonky one compressed and the other normal. As it turned I flicked the lever on the wonky one and the engine ran. Was no impeller or cooling so I didn't run for long. Will go have a fiddle on the super high tide tonight when I have cooling.
Thanks to all on this thread and the problem solving. Couldn't have done it without you!

Well done, and congratulations!

I assumed you had already checked the injectors for spray pattern, etc. An injector is usually a cheap and easy fix, so good thing to check early on. Anyway, glad you found the prob before doing a partial teardown.