Carb strange problem

[kurylenko]

Hi there!
Need some technical advise.
I use in my 29 feet sail boat a Yamaha F15 AMHS year 2004 - 2005
outboard motor. After a total failure of its original carburetor I managed
to buy and adapt a new carb used in 2006 and later F15īs. It performed very
well, for about five years.
After that it started to malfunction when in idle so I dismantled it, cleaned
all openings I could get to with "ARBO Carburator Cleaner" spray and
then flushed it with WD-40 spray (I donīt trust that ARBO Cleaner)
I have the following situation now: The idle is still irregular and also
the motor, after a few seconds, accelerate by itself, to about 2000 RPM
then, after another few seconds falls back to the idle speed, then in
a few seconds, starts this bahavior again and again. BY ITSELF!
What the heck is this?

[ausnoelm]

Clean the carburettor properly (not with spray) and/or find the air leak.

[TownsendsFJR1300]

Plus 1 on re-cleaning the carb.

Its revving up as its leaning out due to clogged jets, most likely the low speed.

ALL the jets, high speed, low speed, nozzle, etc, HAVE TO COME OUT.

The holes are extremely small and UN-LESS YOU CAN SEE LIGHT THRU THEM, that carb is NOT CLEAN

Part #14 is the main jet, #7 the idle, #14 nozzle:
http://www.boats.net/parts/search/Ya...TOR/parts.html

Make sure a fuel pump is cleaned out of all crap as well or you get to do a third "do over".

[kurylenko]

Thank you for your advise.
What is the "Pilot Screw" (No. 2 on the drawing) for?

[99yam40]

pilot = idle /low speed

[TownsendsFJR1300]

+1 ^^^. Its for fine tuning the idle mix. As you can see, its under a cover, generally not messed with...

[kurylenko]

OK, thank you folks but ... just as a curiosity, how can the motor
accelerate by itself then fall to the idle speed then accelerate again, all
over and over without nobody touching it?
Yes I checked the float and the needle, they are ok.

[TownsendsFJR1300]

just as a curiosity, how can the motor
accelerate by itself then fall to the idle speed then accelerate again, all
over and over without nobody touching it?

Crap floating around the inside of the carb, clogging jets, leaning out(will raise the low speed when runnig out of gas).

Did you physically check the jets?

[99yam40]

Timing changing will change RPM also
easy to monitor with a timing light