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mercury thunderbolt 85hp

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frankie 69

New member
Hi all, new to this site and anything else to do with engines thats why i have a question for anyone out there!!!
i have a 1974 mercury 85hp thunderbolt ignition which until the other day has been fantastic for an old school engine, starts fine idles great good compression and spark but when put into gear under load she cuts out and the only way it will keep running is by turning up the idle screw but the revs are to high and clunks into gear and i'm afraid it will damage the gear box. any ideas.......
many thanks
 
If backing out the idle screws doesn't work then time to clean and rebuild the carbs I think.And just for peace of mind have a look at the fuel pumps as well.
 
Have you tried opening the idle mixture screws ?--Have you replaced water pump recently ?--------Done a compression test ? -------confirmed that you have good spark on all 4 cylinders.--------Maybe just as simple as a bad sparkplug too.
 
hi both ,yes compression good spark good not replaced water pump recently and opened idle screw but still no good so i guess its down to cleaning out carbs etc .i live in the uk so getting parts could be difficult i've been told is this true ????
 
Easy to get parts where I am.------Clean the carburetors and inspect as much of the reed valves while carburetors are off.--Pump impeller should be replaced on a regular basis.----------Definitely every 4 / 5 years or even sooner. There is no overheat warning system on that motor !
 
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I live in Ireland,I can get spurious/after-market from http://www.marineparts.ie/ or as I do,I send to the 'States for the genuine Quicksilver. www.maxrules.com , www.oldmercs.com ,and take a chance on the customs.If you go to a Mercury dealer in the UK,they are unlikely to have them in stock but "will have them in a couple of days",by doing exactly what you will do on the net and double the price. You can probably get them here on this site,but I'm not sure if they ship international.My obsession is a 1969 Merc800
 
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