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1978 mercury 85 hp 16ft cee Bee hull

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brad

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" I have a problem with full t

" I have a problem with full throttle it doesn't want to go. I cleaned out the carbs that didn't work. I rebuit the fuel pump, took a compresion test it's fine. My gas tanks are metal and are supposed to have vents but i crack the lid at full throttle and the same thing happens slow speed. i pull the throttle up making it 3/4 and it starts to run better. When i pull the choke up 3/4 speed it gets 3200 rpms. When i put the choke down it slows down as well back to 2300 rpm. When i spray carb cleaner into the lower carb hole its picks up speed to 5000 rpms. Then when the spray stops the speed stops. I also sprayed the top carbs to see if it did the same thing but nothing happened. Also when u stick your fingers in the bottom carb it starts to speed again. Are the bottom seals bad. Are they called the lamberg seals or something like that. "
 
"Brad.... Mercurys are not my

"Brad.... Mercurys are not my line of expertise but your problem is a common one. It appears that you've overlooked something in the lower carburetor, possibly a high speed jet (My Opinion).

I'm sure a qualified Mercury tech will jump in here to pinpoint the problem.

Joe
"
 
"Brad,

I would have to agre

"Brad,

I would have to agree with Joe here; there must be something you overlooked in that carb.

On the front of the float bowl, at the bottom, you can see a brass plug/main jet assembly. You can remove it without taking the carb off. The main jet screws into this assembly from the aft end. It has a tiny hole for fuel to pass through. Make sure it is clear, and that the whole assemlby is free of sludge. It sounds like the problem must be here, but it could also be that the float or float valve are not working properly, or not adjusted properly, so that very little fuel is getting into the carb.

"
 
" Tony,

I'm not su

" Tony,

I'm not sure how the linkage for those carbs go.. if he still doesn't manage to find the problem, would it be possible on that engine to easily switch the top and bottom carb? Assuming that the problem followed the carb, that could be a way to definitively point to one carb.

Jon "
 
" Hi Brad; I would start with

" Hi Brad; I would start with checking the tank (Rust)and fuel line from the tank. you might want to change the line if it's 5+ years or more, you do have vents on the gas cap that need to be open. If your motor runs ok if you got 5000 rpm when you hit the carbs, I would think it's befor the carb, go plastic tank $20.00, walmart has the line with bulb, and fittings $13.00, sounds like a cheap fix.let us know.... "
 
" Hello all,

Everyone has m

" Hello all,

Everyone has made good suggestions here
Brad. You should consider all of these possibilities. You seem convinced that the problem is related to the bottom carb, and from what you said it does seem to me that you are on the right track. One point I would add here is that the problem might not be the carb itself, but something that is isolated in the bottom cylinders. Broken reed valves are a possibility, but I don't think that spraying fuel into the carb would help that condition. And when you say that putting your fingers into the bore (this is the same as choking the carb) helps, it leads me to believe that the reed valves are okay, because there must be good vacuum or choking would not help.

Did this condition pop up suddenly, or has it been developing over a period of time?

Jon's idea is a good one. I think you could switch carbs on that engine, but you might have to improvise a little. The fuel connections might be different on each carb, but I'm not sure about that. In the parts manual, it calls for two identical carbs.

Tony "
 
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