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Old 26 October 2014, 15:29   #1
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Yamaha 30 stalling when revs are low

Hi,

I took my SIB out today and I had a couple of engine problems the first problem is when starting. It'll start but will die when I put the throttle to idle (just below the START mark) and it's had this problem since Wednesday (before that it was run be the previous owner and it was fine). The second is it will die when the revs are low (anything below about 950) or when put into gear with low revs. It has no problems when in gear at WOT other than it seems to lose power a bit... any ideas on what this is? Sorry for the long winded story but as they say a picture tells 1000 words! It's a Yam 30DMO 1991 (picture of serial number attached)
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Old 26 October 2014, 18:48   #2
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Check if the prop turns freely out of gear you might have rope/ twine caught between prop & gearbox
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Old 26 October 2014, 20:19   #3
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If you haven't changed anything (like the prop) then it sounds like the idle jets....

If it's been stood a while then the fuel can go gummy in the carbs. when you power up to full throttle then the main jets are used which is a different circuit, which should run fine, but when you drop back down the revs you use the idle circuit again.

Sounds like the carbs might need a clean?

If it is the carbs then the ultimate carb clean is done in an ultrasonic bath
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Old 26 October 2014, 20:21   #4
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Having said the above it could just be adjustment required?

But if you're the new owner then you wont really know for sure.
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Old 27 October 2014, 00:47   #5
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^ I would start with an adjustment of the carbs and see if it makes a difference. If not then rebuild the carbs.
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Old 27 October 2014, 02:10   #6
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The previous owner did strip the carbs completely but I will start with the carbs. Would it be worth running a carb cleaner through them to see if that helps? What would I need to adjust on the carbs?
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Old 27 October 2014, 06:41   #7
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Decided to check the spark plugs this morning (which were new last week) and would I be right in saying it appears to be running a tad rich? Pictures are in order from cylinder 1 to 3.
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Old 27 October 2014, 07:07   #8
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It's difficult to advise over the internet but assuming that the carbs were cleaned correctly then I would check the pilot screw adjustment on each carb.

You will need to find out the setting for your engine but it will be something like 1 1/2 +- 1/4 turns out from lightly seated.

How you do this:

Locate the pilot screws (one on each carb) and wind them into the lightly seated position counting exactly how many turns it took before the screw hits the seat. As above this should be around 1 1/2 turns +- 1/4 of a turn.

The smallest adjustment on these screws can affect the running of the engine so it is important to take note of where each screw was before you started to adjust them.

If you find that it takes more or less turns than recommended for your engine on each screw, then this is more than likely the problem.
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Old 27 October 2014, 07:11   #9
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Cheers whisper! I'll give that a go and see if it helps
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