mercury thunderbolt 85hp

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darren frankland

Recruit
Joined
Apr 28, 2012
Messages
5
hi there, just joined the iboat forum what a site . i'm from Wales in the uk and have a question i would like help on pls!!!
i have an 1974 85hp mercury thunderbolt engine old school but runs fantastic till the other day, starts great idles fine but when put into gear cuts out ,compression fine spark great any ideas would be great !!!!!!
thank you
 
roscoe

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,921
Re: mercury thunderbolt 85hp

Welcome darren.

It may be something as simple as the idle speed being a tad bit too low.

Or a loose wire in the shift controls, causing the "kill" circuit to cut off the ignition.
 
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darren frankland

Recruit
Joined
Apr 28, 2012
Messages
5
Re: mercury thunderbolt 85hp

good evening, many thanks for getting back to my question. i've tried turning up the idle screw but to get it to go into gear without it cutting out the revs are way to high for it to engaged gently into gear and i'm afraid it will damage the gear box. could it be carbs ??????
cheers
 
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TyeeMan

Master Chief Petty Officer
Joined
Feb 27, 2006
Messages
849
Re: mercury thunderbolt 85hp

You should maybe re-post this in the Mercury Outboard forum, you'll probably get a lot more answers there. Or maybe a moderator could move it.
 
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darren frankland

Recruit
Joined
Apr 28, 2012
Messages
5
Re: mercury thunderbolt 85hp

ok many thanks,iv'e just put question out on marineengine.com mercury forum so fingers crossed .
cheers
 
merc850

merc850

Commander
Joined
Jul 7, 2010
Messages
2,055
Re: mercury thunderbolt 85hp

The low speed should be set under load in gear at about 1200 rpm. Start with the idle speed needles about 1 1/2 turns out from seated then turn them one at a time until the engine runs smoothly. That idle screw in front of the distributor is to set the Neutral idle not the running idle, engine should idle in N at about 900 rpms.
 
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darren frankland

Recruit
Joined
Apr 28, 2012
Messages
5
Re: mercury thunderbolt 85hp

many thanks chief petty officer ( 850 merc ) will give it a go but not holding my breath !!!!!!
 
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darren frankland

Recruit
Joined
Apr 28, 2012
Messages
5
Re: mercury thunderbolt 85hp

Hi all, just to let you know that i cleaned the carbs like you said but still the same but now i have what looks like oil in my tub that i use for running the engine in and now it won't start !!!!!!! :confused:
cheers
 
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