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Old 10 October 2010, 17:50   #1
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Idle mixture adjustment on 90HP yam(2st) 2006

My new engine works otherwise perfect, starts easy, very smooth under load but seams to have a fuel related issue on idle. Poor idle and and might shut down unless increasing the rpm over normal idle. No difference warm or cold. Fuel filter ok, sparks ok, pretty sure its carb related. Burned 60 l gas today at good load but still the idle was not optimal.

Have located the idle mixture adjustments screws. Any hints what is the basic setting(how many turns from closed) and any tricks how to get all 3 carbs tuned.

Not excluded to take engine to service, but rather try first the DIY way. Thanks
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Old 10 October 2010, 18:33   #2
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There are many more people with more experience of Carb related problem solving skills on here than me, but sounds like several possible problems to me. If I were you I would have all three carbs inspected and cleaned. Even if filtered fuel is used there is a chance that old fuel has left a residue of varnish like coating inside your float chambers and a piece of this might have got sucked into the mixture and Idling gallery's of one or more of the carbs. It's worth checking this first for peace of mind.

Once you are happy that the carbs are clean then you'd have to get some info on mixture settings and complete this. Then go about balancing the carbs. This can be done using Vacuum gauges or if you have a good ear and have experience of balancing, a piece of pipe so you can listen to the air flow into the mouth of each of the carbs.
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Old 10 October 2010, 18:43   #3
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Quote:
Originally Posted by C-NUMB View Post
but rather try first the DIY way.
As a start, idle screw barely opening the butterflies, mixture screws all the way in, then one and half turns out.

Leg needs to be in a bosh, not on muffs.
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Old 11 October 2010, 14:57   #4
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Thanks for comments/advice. Checked also the price for having the carbs balanced /tuned by a yam dealer, 75 euros. Can live with that one if it will sort the issue. As not (yet) having a repair manual might be a good choice to have it done by a pro.
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