# Boat slows down when full throttle...after new lower unit installation



## Redfisher80 (Jul 17, 2017)

Could be a few things....start with these....they cost nothing to check.

-too much gear case oil
-air in the lower unit (pressure)
-bad shims on the lower unit gears
-gear shifter not fully engaging (cable adjustment)
-loose fly wheel

I would check these out before going any further.
Redfisher


----------



## Redfisher80 (Jul 17, 2017)

One other question....does it bog down (still have rpm) at wot? 
Also could have nothing to do with the lu. Could be the high speed jet in the carb being clogged or a clogged fuel filter.

Redfisher


----------



## Redfisher80 (Jul 17, 2017)

Also could be a bad ground cable....check that as well. I had this same issue on a 2 stroke mercury 50 in 2001. Changed the entire cable from the battery to the motor and that fixed the issue.

Redfisher


----------



## Campbell Hallett (Jul 11, 2018)

Campbell Hallett said:


> yea itll run at about half speed when the hammer is down





Redfisher80 said:


> Also could be a bad ground cable....check that as well. I had this same issue on a 2 stroke mercury 50 in 2001. Changed the entire cable from the battery to the motor and that fixed the issue.
> 
> Redfisher


Yea it'll run about half the normal RPMs when the hammer is down, but it will run full RPMs when the throttle isn't all the way down, too. Never bogs down completely.


----------



## Campbell Hallett (Jul 11, 2018)

I can get a video of it up tomorrow night


----------



## Guest (Jul 12, 2018)

Sounds almost like your throttle plates are going past wot at wot. Remove your silencer and look down the carb throats, at wot the butterflies should be flat.


----------



## lemaymiami (Feb 9, 2007)

Whatever mechanic said "you might have to break it in".... is out to lunch.... I'd find another tech - someone working for an authorized Yammie dealer....

Any one of the previous suggestions might be your problem. You need an experienced factory trained tech to take a look at it for you... You could fix lots of stuff that won't need fixing otherwise... A properly installed lower unit should have no effect on how your powerhead is working...


----------



## g8rfly (Oct 9, 2011)

sounds like you have a console/wheel, but I had a similar problem with my tiller after a service, and it ended up just being the throttle/assembly cable. Word of advice, start with the easy stuff on the list and work your way through the hard stuff. And yea, as capt said above, time for a new tech!


----------



## Campbell Hallett (Jul 11, 2018)

Thank for all the help. I'll take a look at it this weekend. Appreciate it.


----------



## RunningOnEmpty (Jun 20, 2015)

Full rpm's at partial throttle and then it bogs down at full? Are you getting your normal top speed when it's getting high rpm's? If yes it's got to be a linkage issue with the throttle control. If the gear case was binding up at full throttle it would have all kinds of metal in the lube. I bet it's simple.


----------

