1986 Merc 90 HP 6 CYL Tower of Power Idling at full throttle

Connermcd4516

Recruit
Joined
Feb 6, 2013
Messages
2
Just finished rebuilding the carbs on my merc, and am running into a throttle issue of some sort. With the throttle fully closed (at idle) the motor will rev up to a very high rpm on its own. I know the floats/jets are mechanically intact, but this has to be some type of fuel problem. I have posted a video to give everyone a better idea. I'm stuck on whats going on, any help would be more than appreciated. Thanks!

https://youtu.be/IZKuEe3CaOE
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Check the primary pickup timing. Your motor should be 0-9* ATDC with the carbs closed, but ready to open. If you have that timing set correctly, use the barrell nuts on the throttle cable to back off the timing until you get about 1000RPM on the flusher,

Are you using the choke when starting it. She took a bit too long to start, IMO.
 

tommarvin

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Nov 22, 2015
Messages
999
Somethings not right with the carbs, For some reason unknown to man , it's not that easy to rebuild carbs,its harder than it looks the first time..
I would watch EVERY video on you tube how to rebuild carbs. Don't just watch one video and go for it, i learn something on every you tube video i watch.
Did you clean everything, and install the rebuild kit.
Sorry,did it worked before you rebuilt the carbs.?
 

GA_Boater

Honorary Moderator Emeritus
Joined
May 24, 2011
Messages
49,038
Somethings not right with the carbs, For some reason unknown to man , it's not that easy to rebuild carbs,its harder than it looks the first time..
I would watch EVERY video on you tube how to rebuild carbs. Don't just watch one video and go for it, i learn something on every you tube video i watch.
Did you clean everything, and install the rebuild kit.
Sorry,did it worked before you rebuilt the carbs.?

Watch EVERY Youtube video about carb rebuilding. Are you serious? Conner wants to go boating some day.

Conner - In addition to what Chris advised, one other thing is make sure the carbs are tight on the intake manifolds, an air leak can cause funny operation
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,047
Those carburetors are elegantly simple.-----It does not take much of a carburetor opening to make this motor run at high revs in nuetral.-------So are all 3 throttle plates closed, yes or no ?
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
?“MerCruiser 90hp 6 CYL Tower of Power”?

Interesting, a vertical I/O

MOD EDIT - Fixed title for Conner.
 
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