Mercury 850 1973 Blue Band - Stalling in Forward Gear (but not reverse)

stucaz

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Oct 16, 2011
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Hi all, new to the forum but really hoping someone might be able to help me out. I have just bought a boat with a Mercury 850 Blue Band that seems to run smoothly on idle and fine when you engage reverse gear, but as soon as you engage forward it sounds as though the gear is jumping in (rather than a smooth change) and 9 times out of 10 it causes the engine to stall. I've stripped down the carbs and they seem to be fine and clean, adjusted the idle to the correct speed, and adjusted the gear and throttle cables as per the Seloc manual that I have, but still no luck. I've read various threads about carb, electrical and reed valve problems that cause a stall, but I'm wondering if this might be a gearbox problem as everything seems to be fine when you go into reverse? Really hoping someone might have an idea as I could do with avoiding a costly diagnosis from the dealer.

Thanks,

Stu
 

CharlieB

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Joined
Apr 10, 2007
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5,617
Re: Mercury 850 1973 Blue Band - Stalling in Forward Gear (but not reverse)

Reverse gear has slightly less load on the motor than Forward.

You carb idle mixture is still just a hair too lean. Try opening each idle mixture screw just the width of the screwdriver blade slot. Once in Forward gear readjust mixture to Best idle speed, then further open the mixture screws almost another 1/8 turn.
 

stucaz

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Oct 16, 2011
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Re: Mercury 850 1973 Blue Band - Stalling in Forward Gear (but not reverse)

Thanks Charlie, I'll try at the weekend and let you know how I get on.
 

stucaz

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Oct 16, 2011
Messages
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Re: Mercury 850 1973 Blue Band - Stalling in Forward Gear (but not reverse)

Hi again,

Weather has been a nightmare recently so haven't been able to make the mixture adjustment yet, but I've noticed that on the lower carb there doesn't appear to be a mixture adjustment screw, just a recess where a screw could go. The manual shows one, but is there a chance the mixture is only adjusted on the upper carb and the two are linked? or could it be that the screw is missing and that's the root of the problem?

Thanks.
 
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