Rough idle at 900 Rpm

[Lowcountryred]

I have a 2000 Yamaha 115 2 stroke that runs great except for at 900 RPM. At this speed and only at this speed the engine shakes enough to vibrate the boat. the carbs where cleaned but no change. Any ideas???

 

[robert graham]

Re: Rough idle at 900 Rpm

Check fuel pump for bad diaphragm, check plugs for fuel-wet conditions caused by possible bad fuel pump. Compression on all cylinders should be similar within 10% of each other. Are your carbs/timing set correctly? Were carbs cleaned and synched properly? Good Luck and keep us posted!

 

[Lowcountryred]

Re: Rough idle at 900 Rpm

Check fuel pump for bad diaphragm, check plugs for fuel-wet conditions caused by possible bad fuel pump. Compression on all cylinders should be similar within 10% of each other. Are your carbs/timing set correctly? Were carbs cleaned and synched properly? Good Luck and keep us posted!

BTW this only happens when in the water under speed. Not on hose or staying still. Does this bring up any issues?

 

[robert graham]

Re: Rough idle at 900 Rpm

Sorry, I thought you meant that it idled at 900RPM and was shaking. At very low RPM's IN GEAR my motor has some shake to it also, almost like a straight drive car engine when you "lug" it at low speed. I believe that the new 4 strokes have a smoothness advantage over the 2 strokes at very low speeds. I'm not sure what can be done to improve you problem, but some of the experts on here hopefully will have some ideas for you. Good Luck!

 

[wildspeed]

Re: Rough idle at 900 Rpm

My 150txr started to do exactly the same thing few weeks ago, very rought idle speed with a lot of vibration, every thing clear up when a little more throttle applied

 

[Lowcountryred]

Re: Rough idle at 900 Rpm

That is exactly what it does. Run great but not at 900 rpms. It is annoying as it is a no wake speed when the engine seems to buck around. Starts great, runs strong, idles perfectly at standstill but it has this little annoyance. Gonna check the prop to see if it could be causing this and will look into link and sync. Thanks for the replies.

 

[DC20]

Re: Rough idle at 900 Rpm

Just a thought, is the idle speed set to low? Maybe a new ding in the prop?