Yamaha 90 Problems

SimonCh · 12 June 2011, 23:02

Hey folks,

Was out on my mates RIB, boat handling for a diving expedition yesterday. He has the same set up as me - 5.5m Rib with a 90 Yamaha. It idles fine, and ticks along nicely, until you open up the throttle under load, and it just bogs. Sounds a bit to me like the choke is stuck open, as it sounds real deep and throaty, but not sure if this is possible? After dropping divers off, it ran nicely, and this fault occurred intermittently, but seems to be worse with more people and equipment on board. any ideas?

Cheers

Simon

Vandad · 13 June 2011, 00:02

So you said it idles fine. Have you played with Fast idle lever? See if you can easily increase the RPM to like 5000rpm?

Then tilt the motor all the way up and just leave the water intake holes in the water (and make sure the engine pumps the water). Then put it in gear (be careful no body is around as it will spray a lot of water!) and check if it can work normally?

It could be a dirty filter, fuel pump, jet, or timing issue.

SimonCh · 13 June 2011, 08:44

Thanks for replying mate,

It rev's fine on the fast idle lever, and we did trim it up, and she revved no bother, but just trimmed itself down as we put the engine in gear! The problem had happened once before so the engine was put in for service, and they put it down to some dirty fuel stuck in one of the jets, so cleaned everything out and thought all was well - but they just ran it without a load so they wouldnt have known.

Strange one!

Nos4r2 · 13 June 2011, 15:15

You won't learn anything from revving it in neutral on a 2 stroke apart from how easily it'll damage it.

Intermittent problems are a sod to diagnose at the best of times.

I'd clean the carbs,change the plugs, check all the wiring connections and see if it helps. If it doesn't, get it in to be fixed as you won't sort it without it being water tested under load.

ribber · 13 June 2011, 16:08

Do you have a bulb in-line on the fuel pipe.

They often play up when they age, rubber not as flexible causing the one way valves to get stuck (intermittently). Worth changing anyway for the sake of a few quid.

Nos4r2 · 13 June 2011, 16:22

Quote:

Originally Posted by ribber

Do you have a bulb in-line on the fuel pipe.

They often play up when they age, rubber not as flexible causing the one way valves to get stuck (intermittently). Worth changing anyway for the sake of a few quid.

Good point. Run through the fuel lines and make sure there's no air leaks there as well while you're at it.

davej · 13 June 2011, 20:33

Not sure about the 90s but my club 115 had frequent problems caused by crap in the tank, which got through the two sets of filters and into the carbs. Until we sorted the tank out, we often had to clean the carbs as some of the jets are very fine.
Davej

SimonCh · 14 June 2011, 13:15

cheers for all the response.

we carry a spare fuel line on the boat, and that was something we tried changing, but made no difference sadly! looks like another trip back to the engine shop for him!

MOS · 20 June 2011, 19:46

Change the fuel pump gaskets.... If that doesn't work, clean the carbs.