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Yamaha 70HP 2 Stroke 2003
Hi,
I have a new to me Yamaha 70HP 2 Stroke (original receipt says 70BETOL, type 6H3L). Purchase receipt (new) suggests 2007, but the label on the engine suggests it may actually have been built in 2003. Tacho says 220 hours only and the engine condition both external and internal appears consistent with this.
Fitted with 703 remote and (presumably) automatic choke.
Sometime it works very well, propelling my 5.4M rib past 30 knots with ease and revving to 6000 rpm under load. Other times however it seems to bog down and can only reach 3000 rpm or so and 15 to 20 knots.
No obvious trigger for good/bad behaviour, although it seems it may be better if put straight under heavy load after a couple of minutes warm up than if run for half an hour at a few knots/2000rpm before going to full power.
In all cases it will rev fine to 6000rpm in neutral - only under load does it struggle. No other obvious issues - good tell tail, no steam or excessive smoke, consuming oil as it should, (digital) tacho not warning of overheat or any other issues and engine does not feel excessively hot.
Not attempted any diagnosis yet - would appreciate any pointers before I get too deeply into things. Initial instinct is a fuel issue - fuel filters, carbs, potentially fuel pump. There is no external fuel filter on the boat, only the one in the engine, which I guess makes an issue more likely).
Any other thoughts/other things to check??
Many Thanks!
Regards,
Rob
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