1983 mercury 70 hp no top end speed

[jamsteno@aol.com]

hi idels good no top speed and used almost 5 gallons of fuel in two miles already cleaned carbs, new plugs, new impeller, new fuel lines, new pump ball, any answers would be appericated.

 

[Dave1027]

Re: 1983 mercury 70 hp no top end speed

That kind of fuel usage definitely indicates something is dumping gas in. Does the primer bulb get full and hard when you pump it up? Maybe the fuel pump is bad and leaking gas into the crankcase? Maybe carb floats not set correctly or needle valves not closing?

 

[ajgraz]

Re: 1983 mercury 70 hp no top end speed

x2 on does the bulb stay hard. Also, is there fuel spewing out the fronts of the carbs?

Describe the running problem more. Does it "bog out" when getting into the 2500-3000 rpm range?

These motors are notorious for ignition component/wiring issues. Have you noticed and issues with battery charging? Have you done any ignition component checks? Do you see any cracked/corroded wiring?

 

[trevans]

Re: 1983 mercury 70 hp no top end speed

Had a similar problem with my 83 70hp merc. Ended up being caused by the carbs. Rebuilt both of them and in the new rebuild kits from mercury it had upgraded floats from the old foam to plastic. According to the merc dealer they had a lot of issues with the old floats saturating with fuel and no longer floating in the carb bowl even though they look fine. If you still have the old floats I would start there if they are saturated it will hold the needle open more than it should. Hope this helps.