anyone with knowledge of the 83 mercury 70hp top cylinder issue

[big boost]

like i said 3 cylinder 2 carb 83 merc blue belt , im looking for someone who has rebuilt one and hasnt had it burn the top cylinder out of it within a year and who is familiar with tuning these old pigs, runs great it just when i do my run down after every time i take it out. its running leaner and hotter than i like it to be, powerhead is rebuild and want to keep it that way, i have the top carb turned 3 turns from seat and the bottom 2 turns from seat the middle and bottom cylinders r perfect little rich but good for post break in, another thing is i have never taken it full throttle im scared too, just cruise at 4400 i just dont understand how its running so hot up top every single one of these ive seen has this problem please help

 

[daveswaves]

Re: anyone with knowledge of the 83 mercury 70hp top cylinder issue

The carb needle only affects the idle circuit, the high speed circuit has a fixed jet. It is possible that the top carb has a blocked jet, or an incorrect jet. Not sure what you mean by " when I do my run down"

 

[big boost]

Re: anyone with knowledge of the 83 mercury 70hp top cylinder issue

run down as in i take the plugs out and see how she was running after i just had it out. i mean its not like it running bad or anything its just i know all of these run hot up top and i wanna find a fix, i also have a parts 70hp not sure if its the same year but its got an extra little fuel return **** kit up on the top cylinder my 70 dont have that but that parts motor burned up up top as well so i know that really isnt the fix. could i run a bigger drill bit up the jet or something on that top carb something needs to be done tho , also running 35;1 mix ams injector 93 no ethnol

 

[j_martin]

Re: anyone with knowledge of the 83 mercury 70hp top cylinder issue

Why so rich on the oil. Believe it or not, too much oil increases fuel viscosity, cuts flow through the metering jets, and can increase cylinder temperature as a result.

 

[big boost]

Re: anyone with knowledge of the 83 mercury 70hp top cylinder issue

ya maybe with ur quicksiver, im not running 50;1 on a motor with 3 1/2 hours on the powerhead sorry gramps runs like a dream better safe than sorry, and its not hot its lean when i say hot i mean lean sorry

 

[big boost]

Re: anyone with knowledge of the 83 mercury 70hp top cylinder issue

how do u think i blew it up the first time 50;1 quicksiver , top piston rings melted into the piston bottom two were just fine

 

[donzi gt230]

Re: anyone with knowledge of the 83 mercury 70hp top cylinder issue

Drilling jets can actually cause a lean condition because it changes the radius at the entry and therefore the flow of the jet so be careful. And that gramps knows his stuff so I hope that was a funny towards him and not 'at' him. He's right in that rich oil mixes do reduce available fuel and it's two fold; higher viscosity, and the gas is diluted by the oil. Rings melted into piston?-no. Piston melted around the rings?-perhaps. But running lean isn't the only thing that can cause that.

 

[Faztbullet]

Re: anyone with knowledge of the 83 mercury 70hp top cylinder issue

Number 1 major meltdown is the timing is off. Make sure you set the max timing correctly!!!! If you already ran it at 4400 rpm and it didnt melt the timing is close as spark is at max advance and throttle shaft has not opened butterfly completely. If 4400rpm is all it will do at WOT, its loaded to heavy or pitched to high and meltdown is waiting to happen.

 

[HAS]

Re: anyone with knowledge of the 83 mercury 70hp top cylinder issue

Years ago my brother worked at the U.S. COAST GUARD YARD in Baltimore MD.
They had the same problem with the 3cyl. Mercurys burning the top piston, I`ll
give to you from his best memory They drilled and tapped a hole into the water jacket for a hose fitting
some place on the lower part of the block. Another hole was drilled and tapped into
the water jacket at the highest possible place on the block for another fitting, a hose
was run from the lower fitting to the upper fitting to carry water to cool the top cylinder.
He can not remember where the block was drilled and tapped or what size the fittings
and hose were.
This was a long time ago and its all he can remember, hope it helps................HAS