Engine - sudden loss of power

MustRib · 25 July 2014, 21:43

Was out from Seaham today, about 2 miles out of the harbour and at around 25 knots,
the engine power just fell away. Revs dropped from 4000 to 2000.
I thought I had snagged a pot buoy to start with, that same sensation.
Dropped the revs to 0 and put it into neutral straught away.
Engine ticked over fine, looked over the stern but nothing picked up by the prop.
So set off again, got another 300 metres and the same thing happened.
Engine wasn't missing, but revs just dropped away, although it did idle ok.
Turned around and started heading back at low revs.
Then stopped, switched off, waited a few mins and then re-pumped the fuel bulb up, and started up again.
Engine ran fine for next 3 hours at all rev range.
Anyone any ideas on this? Fuel pressure? Checked fuel lines and bulb - all ok and no leaks.
thanks

Rogue Wave · 25 July 2014, 21:48

Did you come down off a wave just before this happened?

MustRib · 25 July 2014, 22:03

the first time yes, the second time going up, the third time flat water.
currently I am telling myself it was the fuel bulb not pressurising properly
or an air lock.....?

spartacus · 25 July 2014, 22:41

Check the Tohatsu fuel hose connection. It's a rubbish design and is prone to seizing. I'd also investigate fuel pump.

Peter_C · 25 July 2014, 22:54

Drop in RPM could be related to the CDI box (Ignition system). Especially if it went to the same RPM during two different instances. Does that motor hold any codes? If so I would get it scanned. The could be list is long. If it is going into limp mode, it could be temperature related, along with a host of other issues.

MustRib · 25 July 2014, 23:04

cheers chaps - will take a look at those things tomorrow

matt h · 26 July 2014, 08:25

Quote:

re-pumped the fuel bulb up, and started up again.
Engine ran fine for next 3 hours at all rev range.

Think you might have found your answer. renew your fuel pump for starters as wise to and check ALL you fuel connectors throughout inc carbs. Likely dirt in cab valve seating or not allowing fuel into float bowls. Very fuel related issue

MustRib · 27 July 2014, 23:03

Checked out the fuel lines, connectors and bulb and everything seems ok.
Gave it a fairly punishing 80 mile run today at some high speeds and it ran very sweetly.

Low Flyer · 29 July 2014, 01:00

Just had same issue with my Yamaha F200, was hairline crack in fuel relief valve,allowing air leak.

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