yamaha 9.9F 2 stroke not nrevving fully when in gear.

rubaiyat

Recruit
Joined
Nov 16, 2015
Messages
3
hi,

have cleaned fuel, pipes, fuel filters etc. starts as normal first or second pull. In neutral will rev freely all the way upto Maximum, sounding fine.. Engage gear and will only rev upto about half maximum. sounds fine, not missing or anything, just slow This happened "overnight" - one day fine, next not fine.

any thoughts please

thanks
R.
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,851
motor needs more fuel to produce power
my guess is your carb needs attention
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,044
Do some trouble shooting.----Sounds like it is running on one cylinder.---Check spark.---Check compression.---Waterpump been looked at lately.----Gas and oil mix at 50:1 or 100:1 on this motor ?
 

rubaiyat

Recruit
Joined
Nov 16, 2015
Messages
3
thanks guys, went over everything I could think of, new plugs fixed it! Old ones were 5 months old with little use and looked perfect .... looks can be deceptive!
 

rubaiyat

Recruit
Joined
Nov 16, 2015
Messages
3
well, after a few weeks the problem returned, in gear only firing on one when revved up. tried new plugs again to no avail. have tried three separate second hand control units, none of which solved it. makes me think problem is not plugs or control unit. is there anything else ?? I am loathe to buy a new control unit from yamaha until i am sure that this is the issue, they are very expensive

ta R
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,851
testing peak voltages like the service manual calls for should tell you if the voltage going into the CDI and the voltage coming out is in spec and a problem or not
 
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