Mercury 850 Thunderbolt 85 Hp Bogging Down

[richcajun70123]

Hope yall can help!! i have a 1976 Mercury Thunderbolt 85 Hp. It ran great a couple weeks ago, then all of a sudden it has starting stalling and killing when i start to accelerate. It starts great carbs are clean but i havent rebuilt them. And my control has not been replaced at all but it does stick the further i accelerate! should i rebuild carbs or try to replace the control box???

 

[Chris1956]

Re: Mercury 850 Thunderbolt 85 Hp Bogging Down

Normally a bog upon acceleration is due to an incorrect carb idle mixture adjustment. How do you know the carbs are clean? Are the floats good?

 

[carholme]

Re: Mercury 850 Thunderbolt 85 Hp Bogging Down

As far as the controls are concerned, disconnect the cables at the engine end and see how they operate. This will help to determine if it is the cables/control box or the engine.

Gerry

 

[richcajun70123]

Re: Mercury 850 Thunderbolt 85 Hp Bogging Down

I supposed the carbs were clean, because the boat ran well last week! Can the carbs get bad that quick? And the control cables move accordingly but I have to punch down on the throttle to get them to move!!

 

[carholme]

Re: Mercury 850 Thunderbolt 85 Hp Bogging Down

Do you know what control box you have?

Gerry

 

[richcajun70123]

Re: Mercury 850 Thunderbolt 85 Hp Bogging Down

Its the original Mercontrol that can with the boat!

 

[carholme]

Re: Mercury 850 Thunderbolt 85 Hp Bogging Down

You can split the box and have a look:

http://www.crowleymarine.com/mercury-outboard/parts/640_28.cfm

Gerry

 

[weezer85]

Re: Mercury 850 Thunderbolt 85 Hp Bogging Down

i have a 1976 85hp 850 doing the same thing what did u figure out on yours thanks for any help

 

[weezer85]

Re: Mercury 850 Thunderbolt 85 Hp Bogging Down

i have a 1976 85hp 850 thunderbolt doing close to the same then mine dies when u put it in gear and wont hardly idle i just got it back from haveing the carbs cleaned and the guy at the boat shop found some bad wiring had that fixed while it was there i got it back and when i put it in the lake it wont hardly run an dies when put in gear it dont do this on muffs any ideals any help will be great thanks

 

[dlp123]

Re: Mercury 850 Thunderbolt 85 Hp Bogging Down

i have a 1972 tower of power that i was having the same problem what i did was rebuild the carbs. what i would try is turn the mixture screws 1/4 turn out till it will run in gear.give it a try mine would run great whit the muffs on but soon as you got to the lake it would bog and die hope this helps.

 

[chum1]

Re: Mercury 850 Thunderbolt 85 Hp Bogging Down

Hope yall can help!! i have a 1976 Mercury Thunderbolt 85 Hp. It ran great a couple weeks ago, then all of a sudden it has starting stalling and killing when i start to accelerate. It starts great carbs are clean but i havent rebuilt them. And my control has not been replaced at all but it does stick the further i accelerate! should i rebuild carbs or try to replace the control box???

if it was running great i would suspect a spark problem causing the bog

 

[weezer85]

Re: Mercury 850 Thunderbolt 85 Hp Bogging Down

i will try that the next weekend im off thank u mine is just like that runs fine on muffs put it in lake dies out thanks

 

[jerryjerry05]

Re: Mercury 850 Thunderbolt 85 Hp Bogging Down

Start with a compression/spark test.
Then all old hoses and connectors replace.
Ethanol is messing with older hoses and connectors.
Rebuild/clean the carbs(usually cleaning is all you need).
Rebuild the fuel pump.
Check the wiring for breaks and missing insulation,bad connections.

 

[CharlieB]

Re: Mercury 850 Thunderbolt 85 Hp Bogging Down

Over time, carbs start getting dirty inside. The motor may start to have a poor idle and be slow to accelerate, but once up to speed seems to run just fine.

Often this is a sign that the very small fuel passsages are dirty enough they are restricting fuel flow, enough to cause the low speed problems.

The main jet, being much larger, does not reduce its flow enough for you to notice any difference in high speed operation.

The cure is to clean the carbs, completely.

Regular addition of SeaFoam to your fuel will greatly extend the time between cleanings, and in some cases can be used to restore idle quality. Relying on SeaFoam to clean your carbs is an iffy thing, as sometimes it will dislodge pieces of crud and almost completely block an idle circuit, then you must disassemble the carb for proper cleaning.

Once the carbs are cleaned, idle mixture MUST BE adjusted ON the water and IN Forward gear, to provide both exhaust back pressure and engine load. Accurate idle mixture adjustment is very difficult to achieve on the hose and NOT for the inexperienced.

 

[weezer85]

Re: Mercury 850 Thunderbolt 85 Hp Bogging Down

any one know where i can order a lower unit / gear case for a 1976 850 85hp mercury thunderbolt?

 

[sutor623]

Re: Mercury 850 Thunderbolt 85 Hp Bogging Down

any one know where i can order a lower unit / gear case for a 1976 850 85hp mercury thunderbolt?

Dude, you need to start your own thread elsewhere.