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Old 04-29-2014, 09:15 PM
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Moto 1986 Yamaha Moto4 225 Carburator Problems!

     

I have a 86 Yamaha moto4 & when you start the four wheeler it is full throttle. I have rebuilt the carb twice now. I have looked on forums and tried a few different things now and I am completely stumped. the float is working moves as it should have tried adjusting idle screw in out. bent the float arms up and down. ive adjusted the needle a few times. and I just cant seem to figure this out. Any help or suggestions would be much appreciated. Ive also checked all air flow to carb throttle cable is clean. Throttle also closes all the way. Thanks in advance for any help possible!!!!

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Old 04-29-2014, 09:32 PM
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Sounds like you have an air leak in the intake system.

Paw Paw
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Old 04-29-2014, 09:38 PM
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I Have checked for leaks everywhere.
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Old 04-30-2014, 01:29 PM
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Remember that your intake manifold seals twice on your model, against
the carb. and again against the cylinder head. Its o-rings are prone to
leaking after years of heat cycling the engine besides normal deterioration.
I suspect, since the float valve assembly seals against the carb body by
an o-ring on its o.d. & that the o-ring is bad, if so.....you can adjust the
float "closed" and it will still pass fuel into the carb coming up through
the emulsion tube & into the cylinder causing it to be "flooded" when that
o-ring or the needle to seat is not sealing 100%!

So, the float valve & its o-ring MUST be in good condition as well as all
the bleed holes in the emulsion tube be clear and the o-ring between it
and the extension that leads into the throttle bore, choke plunger tip
must close & the rubber seal on it functional, the air bleed leading to
emulsion tube also need to be clear and proper size ( I have cleaned
lots of these that had dried fuel residue in them reducing their size &
causing a rich condition) which can be missed in a carb clean....good luck!

PS:

Also your fuel petcock must be functional, it must shut off. If it does not
it means its internal sealing washers are bad, this not only cause it not
to stop fuel flow but often allows small bits of rubber to foul the float
valve from shutting off...& again flooding.
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Old 04-30-2014, 04:19 PM
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All of the seals and o rings in the carb are good the o ring from carb to manfold is good. could exaust not being tight enough cause this? also I have good compression enough to start the four wheeler but could I still be getting air from the head ? Everthing is leading too an air leak somewhere im just not finding where this air is coming from

---------- Post added at 03:19 PM ---------- Previous post was at 03:04 PM ----------

does anyone know how many pounds/psi I should be getting compression wise?
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Old 04-30-2014, 07:31 PM
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Not sure on compression but thats not why it's revving up. Are you sure the carb slide isnt sticking in the carb?
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Old 04-30-2014, 07:55 PM
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yes I am very sure the slide is not sticking. slide all the way down as soon as it starts it is full throttle tried lifting the four and putting it in gear when it starts and still full throttle
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Old 05-02-2014, 01:15 PM
RiV RiV is offline
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Oops I misread your initial statement, I thought you said it must be FULL
throttle to start. Anyways, take the slide off the cable & manually slide
it up and down the bore making sure that it does so freely and has good
engagement with the alignment pin. Make sure that the pin is holding the
cutaway on the lower part of the slide towards the air filter & that with
the idle screw out that the slide closes fully at the engine side of carb.

Also check that the needle is straight and not dragging on the emulsion
tube of the carb & holding the slide open, the slide does not have to be
open very far to act like it is full open when its in neutral-yes I know you
stated the slide is not open but it really sounds like it. Make sure the is
no excess wear on the slide and you cannot see light around the sides of
the slide, that would have to be quite worn but worth checking.
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