Outboard air lock ?

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Caladh

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So there we were stuck on the Dartmouth rubbish skip pontoon unable to start our 3.3hp 2 stroke Mariner which had been a v reliable o/b. This happened during the very hot spell in July. It wouldn’t fire at all and when turning over seemed to drip fuel into the water. Rowed back to our boat and changed the plug. It fired and started albeit very roughly, the plug was old however. I put the original plug back in and all was and has been well. I wonder what happened and how I might prevent it happening again. I did turn the fuel tap on and off and also had released the fuel cap to see if that helped. I’m guess the float somehow stuck closed. Any advice for any future woes ?
 
Dripping fuel does sound like a stuck float/needle. That would also have wet the plug (and stopped it firing) - did you happen to notice when you took it out?

If that's it then there are various causes from pure gritty dirt to jelly coming from ageing fuel. How clean does the bottom of the tank look? (I've fitted secondary filters to my outboards).

ps. Quick fix for a wet plug is heat. Stick it on the hob for a couple of minutes until it's all grey ash.
 
Caladh said:
. I’m guess the float somehow stuck closed. Any advice for any future woes ?
Click to expand...
Fuel dripping suggests the needle valve may have been stuck open, or at least not seating properly.

What the occasional yachtsman says applies.
 
anoccasionalyachtsman said:
Dripping fuel does sound like a stuck float/needle. That would also have wet the plug (and stopped it firing) - did you happen to notice when you took it out?

If that's it then there are various causes from pure gritty dirt to jelly coming from ageing fuel. How clean does the bottom of the tank look? (I've fitted secondary filters to my outboards).

ps. Quick fix for a wet plug is heat. Stick it on the hob for a couple of minutes until it's all grey ash.
Click to expand...
I recall the plug appeared dry when I removed it. I assumed fuel wasn’t getting thru because of an air lock.
 
Caladh said:
I recall the plug appeared dry when I removed it. I assumed fuel wasn’t getting thru because of an air lock.
Click to expand...
It's a simple gravity feed from the tank to the carb which is unlikely to air lock. If no fuel is getting through it's more likely to be the tank vent shut or blocked , or the filter in the tank outlet blocked, but if fuel was dripping it must surely have been getting through.
 
Caladh said:
I recall the plug appeared dry when I removed it. I assumed fuel wasn’t getting thru because of an air lock.
Click to expand...
As per VicS, I can't really see a mechanism for air or vapour locks.

The drips you mention - coming from under the cowling? Could you guess which end, how full was the tank and can you remember the sequence of opening tap, vent cap etc? Apologies if your first post was already an exact description...
 
anoccasionalyachtsman said:
As per VicS, I can't really see a mechanism for air or vapour locks.

The drips you mention - coming from under the cowling? Could you guess which end, how full was the tank and can you remember the sequence of opening tap, vent cap etc? Apologies if your first post was already an exact description...
Click to expand...
Yes under the cowling at the controls end. I probably turned the fuel cock on and off first and then the fuel cap - even though the vent was of course open. I m guessing a carb strip down will be in order.
 
Caladh said:
Yes under the cowling at the controls end. I probably turned the fuel cock on and off first and then the fuel cap - even though the vent was of course open. I m guessing a carb strip down will be in order.
Click to expand...
You said all is well after putting the original plug back in.
If it is now OK don't fix what's not broken. Investigate float and needle valve if yo have any more trouble.
 
Caladh said:
Yes under the cowling at the controls end. I probably turned the fuel cock on and off first and then the fuel cap - even though the vent was of course open. I m guessing a carb strip down will be in order.
Click to expand...
Well that's the carb end and so probably not the tank blowing fuel out under the cowling as you opened the cap with a blocked vent. Vic's comment on leaving it is probably right, the extreme heat may have caused a problem which won't happen again - this year anyway.... If it does it again, yes, carb strip.
 
anoccasionalyachtsman said:
Dripping fuel does sound like a stuck float/needle. That would also have wet the plug (and stopped it firing) - did you happen to notice when you took it out?

If that's it then there are various causes from pure gritty dirt to jelly coming from ageing fuel. How clean does the bottom of the tank look? (I've fitted secondary filters to my outboards).

ps. Quick fix for a wet plug is heat. Stick it on the hob for a couple of minutes until it's all grey ash.
Click to expand...
Not a good idea nowadays. Plugs are coated and that coating can be removed by excess heat,alkylites and wire brushing causing them to fail
 
Caladh said:
So there we were stuck on the Dartmouth rubbish skip pontoon unable to start our 3.3hp 2 stroke Mariner which had been a v reliable o/b. This happened during the very hot spell in July. It wouldn’t fire at all and when turning over seemed to drip fuel into the water. Rowed back to our boat and changed the plug. It fired and started albeit very roughly, the plug was old however. I put the original plug back in and all was and has been well. I wonder what happened and how I might prevent it happening again. I did turn the fuel tap on and off and also had released the fuel cap to see if that helped. I’m guess the float somehow stuck closed. Any advice for any future woes ?
Click to expand...
My 4hp Yamaha 4 stroke misbehaved last week, refusing to start, turned out to be a blocked main jet.
I too noticed dripping what I thought was fuel while I was pulling trying to start it. This turned out to be water from the tell tale.
Just wondered if you were being misled too ?
Dave
 
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