9.9 Yamaha 4 stroke intermittent missing

Catspaw

Recruit
Joined
May 18, 2002
Messages
1
Hi all:<br /><br />This is a strange one. I use the 9.9 4 stroke Yamaha to push my sailboat. <br />Symptoms:<br />- it starts great and idles well<br />- will initially run up to full power<br />- after running approx. 10, 15 minutes develops amiss, similar to quenching a spark plug, needs to be turned down to an idle, any attempt to give more power results in what sounds like running on one cylinder.<br />- after fussing for 5, 10 minutes it catches and then will run cleanly at all power settings for hours<br />- any suggestions are welcomed<br />Thanks so much!<br />Paul
 

hondon

Lieutenant Commander
Joined
Jun 11, 2001
Messages
1,922
Re: 9.9 Yamaha 4 stroke intermittent missing

When is the last time you had the valves adjusted?How is your fuel quality? Clean ,fresh, and water free?There could be a problem with the automatic choke but I would start with the basic maintenance stuff first.
 

Liquid Lunch

Recruit
Joined
Jun 4, 2005
Messages
1
Re: 9.9 Yamaha 4 stroke intermittent missing

My Yamaha 9.9 did exacly the same.<br />After many returns to the dealer whom couldn't fix, it was as simple as replacing the oil presure switch.<br />Problem solved.<br />I have heard of many Yammie oil presure switchs failing after I replaced mine.
 

65Constellation

Recruit
Joined
Jul 24, 2008
Messages
1
Re: 9.9 Yamaha 4 stroke intermittent missing

I've got exactly the same problem. Couldnt explain it better. 'S the darndest thing. Starts well, runs well for 10 min, rough as can be for 10 min, back to good until I shut it down. Doesnt matter most of the time, but when you are running from a thunderstorm, the perspective changes.

I will try the oil pressure switch.
 

Bife

Recruit
Joined
Mar 4, 2008
Messages
5
Re: 9.9 Yamaha 4 stroke intermittent missing

This is exactly the problem that I have had for about a year now.

My 1990 F9.9 (white) is on my 22 foot sailboat

The only difference is that it runs perfectly for any thing between half an hour up to an hour and a half, then starts flipping between reduced revs and normal, eventually staying at running at reduced revs/power. The only thing to do is reduce throttle to idle.

I have been to two different Yamaha workshops who have not found the problem. Both put it in the tank and couldnt find any problem, one ripped me off with a huge bill for adjusting the carb and changing the plugs, both suggested I needed to buy a new engine from them!

I have clenaed the carb out n times and adjusted the float level, replaced inlet manifold gaskets.

I am at a loss - anyone have any more ideas?

Where is the Oil Pressure switch?

I am in Portugal, the motor was originally from Holland I think.

Please help, I haven't been that bothered up till now, but now that we have a 2 month old new crew member called Mary, I am a little bit more worried!

Thanks

Bife
 

robert graham

Admiral
Joined
Apr 16, 2009
Messages
6,908
Re: 9.9 Yamaha 4 stroke intermittent missing

Maybe fuel delivery, gas tank vent, primer bulb/check valves in good shape, fuel pump, fuel filter, air entering fuel line? sticky carb float needle valves could cause what you describe. Good Luck!
 

robert graham

Admiral
Joined
Apr 16, 2009
Messages
6,908
Re: 9.9 Yamaha 4 stroke intermittent missing

Next time it does it, sqeeze your primer bulb to see if that helps.
 

Bife

Recruit
Joined
Mar 4, 2008
Messages
5
Re: 9.9 Yamaha 4 stroke intermittent missing

Thanks Robert,

I have tried squeezing bulb but it didnt work. Also tried with cap off of gas tank. Fuel filter been changed.

But, the bulb does leak a bit if i press it when its hard, and didnt always pump well, so will chase that up.

Some other ideas there for me to think about too, thanks!
 

Bife

Recruit
Joined
Mar 4, 2008
Messages
5
Re: 9.9 Yamaha 4 stroke intermittent missing

reading more related posts around the forum, maybe it is the oil press cutout sensor?

mine has a sensor that seems to feed the green oil press light, but i cant find the cut out sensor.

can anyone tell me where exactly where it should be, or if all f9.9 motors had this?
 
Top