Seeking advice on throttle problem with Yamaha 9.9hp outboard.

[NealB]

Our catamaran has a Yamaha 9.9hp 4 stroke high thrust outboard as an auxilliary.

During our summer cruise it worked perfectly as we cruised from Plymouth to the Isles of Scilly.

On the way back, we decided to put into Fowey. The engine fired up first time (as usual), and we lowered sails as we made our way up river.

There was a fair bit of river traffic as we approached the moorings, so I moved the morse type single lever control to the 'tick over' level. Strange....the engine continued revving at a highish rate, and we sped along too fast.

At this point I may have done the wrong thing, by forcing the lever to the neutral position...it needed a real 'heave' with both hands. The gears disengaged with an almighty bang (really, you had to be there to believe how loud it was), and the engine now revved deafingly, but in neutral.

Hmmm.... at least we slowed down!

I switched the engine off, and rehoisted the mainsail.

As we drifted along I took the engine cover off, and found that I could operate the throttle at the carburettor end, and we picked up a vistor's buoy.

Here's the symptoms:

- When the engine isn't running, the throttle lever works perfectly to close the throttle (so I think the cable is working ok).

- When the engine is running in neutral, the lever drops the revs down a bit, but not right down to idle.

- When the engine is running in gear, at medium to highish revs, the revs barely drop at all as I move the throttle lever.

The spring at the carberettor end looks and feels ok.

I rigged up a bit of curtain wire to assist the spring, which is still performing well, but I'd like to get things working properly again.

I'm baffled as to why the symptoms are different when the engine is running.

Any thoughts on what I should try?

Thanks!

 

[tross]

Silly question - does the engine move when the gears are engaged trapping the cable some how - or is there an interlock that prevents the gear being engaged when the throttle is not at idle and is sticking?

 

[earlybird]

[QUOTE.
I'm baffled as to why the symptoms are different when the engine is running.
Thanks![/QUOTE]

Just a suggestion, but the throttle slide or whatever in the carb. will have a pressure drop across it when the engine is running, hence more friction for the return spring to overcome.

 

[alahol2]

From those symptoms I'd say the problem is almost certainly in the remote control unit. Something has come loose or is catching.

 

[billcole]

I've just had problems with the throttle sticking open on my Yamaha 6HP of early-mid 1990's vintage. This was caused by a small amount of corrosion that had formed where the brass throttle shaft turned in the aluminium carburetter body. This was invisible until I took the carb off and drew the shaft out of the body (it's held in place by a circlip on the opposite end to the control linkage ).
Cleaning the brass shaft with Brasso, and the hole in the aluminium carb body with a cotton bud soaked in contact cleaner, followed by reassembly with a little grease has made it much more free-moving. Compare yours with the choke operation, they're very similar in construction, and the throttle shart and choke shaft on mine are now equally free moving.
If this is the source of the problem then I can only guess that the temperature change when the engine is running might be causing the difference to when it is stopped.
By the way, I don't know if the 9.9 is the same as the 6, but to get the carb off on my engine you need to first take off the front panel insert which has the choke and the fuel connector mounted on it, and this gives access to the bolts holding the air intake silencer and the carburettor on to the engine.