9.9 4 stroke rough idle

[knot trying]

My 2002 F9.9 MH series just started acting up. The symptom is that it has a very rough idle and low speed performance when in gear.

It starts fine, idles great in neutral and runs good at WOT.

I'm guessing that it has to do with carb or fuel pump but could use some pointers as to where to start troubleshooting.

Thanks.

[boats.net]

Check the fuel filter for water or trash. Check idle rpm should be 950 rpm's in neutral. Next step would be to remove and clean carb.

[sherwin]

9.9 4 stroke rough idle

Sound like something my T9.9 is experiencing. In my case there is a lack of
power until I turn the throttle handle to about the midpoint. I orignally thought
this might be a throttle cable problem, but now I am more inclined to guess it
is the high speed jet of the carb. I had many problems last season where I had
to tear down my carb 3 times to clean the idle and high speed jets. I have
had better results this season by changing out my fuel hoses and putting in an
inline 10 micron filter. However, I still have this residual problem of lack of power. Like your 9.9, the engine idles fine and runs smoothly once it gets into
the higher revs. I think this whole 4 stroke 9.9 series engine has design faults,
judging from all the problems I see on this board and my own experiences. Of
course, Yamaha would be the last to admit this. I'm tired of tearing down my
carb, so I will try and live with this current difficulty, until it gets worse.

This is my second retyping of this reply, as the first one was completely erased
upon submital, and I couldn't get it back.

[knot trying]

sherwin

This is the first problem I have had with the carb. Had some spark problems that turned out to be the plugs.

When you did your carb rebuild, did you have to replace any gaskets? I'm contemplating removing it to clean the jets and I could not find a rebuild kit listed as a single item so I guessing that at a minimum I will have to replace some gaskets.

I'm also going to try some carb cleaner in the gas to see if it will remove any gunk without doing the major carb surgery. Could be some grunge dislodged and got into a jet.

If I have success, I will post the results.

Thanks.
kt

[sherwin]

rough idle

Hi KT,

I did not exactly rebuild the entire carb. Just took it apart so I could get to the
jets. I watched how a competent mechanic cleared up my problem by running
a fine wire through the idle jet and high speed jet. I simply mimicked him. I saw
no need to replace any gaskets for this operation. I tried the carb cleaners and
had little success with them. Once dirt gets into the fine jets of this four stroke, it takes a poke to get them out. I would advise using stabil in your
gas tank, installing an inline 10 micron filter, and replacing any questionable
components of your fuel delivery system (tank, hoses, etc.) I have to check
the filter inside the engine, as I am experiencing some throttle delay problems.
Otherwise, I have not had to clean the jets since the three times last season.

Sherwin