Engine Trouble

[A1an]

Originally Posted by neil.mccrirrick

If all the electrics pan out I'd be looking at a sticking valve, when it starts missing if you are able I'd pull a plug cap off to try and narrow down which cylinder is dropping off. Or stop the engine when missing and see if you can tell from the plugs which one is oiling up.

If you can suss the cylinder you can isolate parts.

The possibility of a sticky valve was looked in to. I couldn't replicate the same rotational speed of the cam as when the engine is at idle but I couldn't see and evidence of a valve hanging.
Compression and leak down tests confirm.

[Pikey Dave]

Does it have an oil level switch? I had a similar problem with a Honda powered genny, I know it’s a different beast, but it turned out to be an over sensitive oil level switch. This goes to earth on low level & earths the ign circuit & cuts the engine.

[A1an]

Originally Posted by Pikey Dave

Does it have an oil level switch? I had a similar problem with a Honda powered genny, I know it’s a different beast, but it turned out to be an over sensitive oil level switch. This goes to earth on low level & earths the ign circuit & cuts the engine.

No oil LEVEL switch bit it does have an oil PRESSURE switch. The CDI does recieve an input from the switch but will only put engine in to limp mode above 1500 rpm, if the engine is below 1500 it will have no effect on timing.

[neil.mccrirrick]

I’d still want to pull a plug when it acts up Alan. If they all look the same you know it’s electric for sure. If one is oiled up you can at least isolate an area. I think it’s fuel delivery given it frees up and runs ok. So auto choke is kicking in or a cylinder is starved of air

[gpsguru]

Originally Posted by A1an

Its a four stroke, I don’t know of a Honda two stroke outboard.

I am aware an impeller change won’t sort an electrical issue.

It has been tested on the Orkney Longliner it belongs to.

I haven’t tested output voltage yet, I’m waiting on a DVA adaptor for my multimeter.

Issue appears under hot or cold conditions.

I have purchased an identical engine tonight, I will swap parts from it until I find the culprit then sell it on again. I don’t want to start buying individual parts and be stuck with them when they don’t sort the issue.

Just a hunch ..... change the rectifier, an intermittent fault on that unit would cause the CDI to get a partial DC supply with a load of AC ripple and CDI units get very upset about that ............

[Last Tango]

Dickie kill switch. Try disconnecting or by-pass.?

[Davie]

Alan, I have had a similar issue on a Yamaha 9.9 and at wits end but wouldn't give up. Granted I have access to engines exact same so easier for me to change but I changed every electrical part inc harness and flywheel, no different Turned out it was a broken valve spring. Was nuts as it had exact same compression when pulling the chord.

On Honda 8 I had one that the plate behind the inlet manifold had split and water was getting from the exhaust into the inlet side and caused a similar issue to what you have but you could see water droplets on the spark plug.

Keep the faith!

[A1an]

Originally Posted by Davie

Alan, I have had a similar issue on a Yamaha 9.9 and at wits end but wouldn't give up. Granted I have access to engines exact same so easier for me to change but I changed every electrical part inc harness and flywheel, no different Turned out it was a broken valve spring. Was nuts as it had exact same compression when pulling the chord.

On Honda 8 I had one that the plate behind the inlet manifold had split and water was getting from the exhaust into the inlet side and caused a similar issue to what you have but you could see water droplets on the spark plug.

Keep the faith!

In the nicest possible way...Im glad it had you stumped as well.

Im waiting on the courier delivering an identical engine so il be going through the swaparoo process.

I had thrown out the idea of it having any mechanical issues due to the comp test coming back spot on, I did whip the valve cover off but that was AFTER the compression check so just had a general squint about, Il check again with more attention, maybe I missed it.

Id be doubtful of the exhaust plate, plugs are spot on and I've bore scoped the chambers, no sign of water but Il check that too. I'm at the stage I'l check anything.

[A1an]

Originally Posted by Last Tango

Dickie kill switch. Try disconnecting or by-pass.?

Yep, bypassed.

[A1an]

Originally Posted by neil.mccrirrick

I’d still want to pull a plug when it acts up Alan. If they all look the same you know it’s electric for sure. If one is oiled up you can at least isolate an area. I think it’s fuel delivery given it frees up and runs ok. So auto choke is kicking in or a cylinder is starved of air

No auto choke Neil, old school. The bit that is throwing me is that the timing light indicates that the plugs are receiving half the pulses they should but everything checks out electrically.

[neil.mccrirrick]

It must be the ignition coil then either broken down insulation that will mean all is good when the engine is cold but as it warms up will allow the current to reduce and lead to a weak spark or the ignition coil is worn out itself. Apologies if you’ve already gone there but that’s where I’d go next

[A1an]

Originally Posted by neil.mccrirrick

It must be the ignition coil then either broken down insulation that will mean all is good when the engine is cold but as it warms up will allow the current to reduce and lead to a weak spark or the ignition coil is worn out itself. Apologies if you’ve already gone there but that’s where I’d go next

It’s been swapped for a known good one with no change to running problem.

Whilst running the engine in the tub the water turns black from the soot of rich running. Plugs are also sooty.

[A1an]

Plugs identical if a little black.

[neil.mccrirrick]

Weak spark black plugs that’s what you would expect. Compression is good so seals should be good. It could still be a worn or broke valve spring or bad float if it’s carb or bad needle. The spark comes from the coils as I’m sure you know. If it’s wired correctly not reversed and insulation is good I’m stumped sorry

[jeffstevens763@g]

pressure relief valve in the fuel pump not reliving pressure, allowing it to push fuel past the float needle?

[Fenlander]

Just to clarify something I asked near the start...

When it misfires and you have the timing light clipped to a plug lead does the light stop pulsing with the misfire indicating lack of spark at that moment?

[Pikey Dave]

Dodgy pickup or gap on the flywheel?

[A1an]

Originally Posted by jeffstevens763@g

pressure relief valve in the fuel pump not reliving pressure, allowing it to push fuel past the float needle?

That's an angle I hadn't looked at.

[A1an]

Originally Posted by Fenlander

Just to clarify something I asked near the start...

When it misfires and you have the timing light clipped to a plug lead does the light stop pulsing with the misfire indicating lack of spark at that moment?

correct. The "bang" correlates with the timing light.

[A1an]

Originally Posted by Pikey Dave

Dodgy pickup or gap on the flywheel?

The trigger coil detects tabs on cam pulley, I have set these tabs as per spec. The exciter coil under flywheel is not adjustable as the coil sits on dowels.

The trigger coil is basically an electronic switch, these do deteriorate and can give intermittent problem whereas the exciter coil just makes electricity, generally these work or don't, it is possible that it's not making the correct voltage, still waiting for an adaptor for multimeter.

Tbh it will be the exciter that I change first, gut feeling.