old mercury woes

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  #1  
Old 06-26-02, 03:15 PM
Marc38
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old mercury woes

hello, I'm new to the board and am wondering if anybody can help me out. My fishing buddy and I recently purchased an older boat with an old mercury 50HP outboard. It has the old thunderbolt ignition if that gives any idea of the time frame as I do not know the exact year of the motor. the problem we are having is that at full speed the boat runs great but when we slow down to troll we seem to be loading up (there's a smell of gas) and the motor shuts off. the carbs were rebuilt less than a year ago and they were sprayed with gumout to eliminate the possibility of a sticky float.
 
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Old 06-27-02, 09:52 AM
telco tech
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I'm not familiar with your motor, but most carburators will have two fuel mixture adjustment screws. One for high speed, one for low speed. Reason for this is that one metering jet can't provide good mixtures over the entire range of operation. Sounds like you may be running rich from the idle jet. It is usually adjustable, but the adjustment screw is often located behind a small metal plug that must be pried or drilled out to gain access. You will have to buy another plug to replace it will you are done ( their cheap)
 
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Old 06-29-02, 05:54 AM
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Hello Marc38 and Welcome to the boating forum and our web site.

Based upon the problem description, not only could the fuel jets be incorrectly adjusted, as mentioned by Telco Tech, it's also a possibility the carbs float level is adjusted too high.

Adjusting the fuel jets via an external adjustment most likely will not resolve the problem you described. The actual problem may just be too much fuel in the fuel bowl.

Too much fuel in the carb bowls or an overly rich fuel supply often allows an engine run well at high speeds. However, this type of overly rich fuel mixture condition may also flood the engine at idle, flood during low to mid range engine speeds and after rapid deceleration.

On most older engines, there should not be any need to drill-out caps or plugs installed over the fuel adjustments screws. There most likely is some sort of removeable cap to cover, hide and or protect the adjustment screw from water corrosion.

Another rare and remote possibility could be the engines ignition spark advance. If the engine in question uses a mechanical spark advance, inside the distributor under the cap, the spark advance weights could be sticking or hanging up while retracting.

Our resident boat repair professional will have additional helpful information, suggestions and advice. Check back on your question several times for additional replies.

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