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Discussion Starter #1
Hi all, I have a Mercury 40 HP that I am having some trouble with. It idles fine, runs good at mid-range speed, but when I put the throttle down, it will run good for about 30 seconds, then bog down. It doesn't stall but does seem to surge a bit. If I back down to idle, it will run fine. Drop the hammer again and it does the same thing. Any ideas on what might be a cause? May just haul it over to Alexander's Landing and quit trying to fix things myself. Thanks in advance.

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Discussion Starter #4
Its a 1995, 4- cylinder.... How do you unstick a needle?

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I'd have to see a pic for sure. But most carbs you remove the bottom bowl and take the float out the needle sits on top of the float arm. There should be an adjustment screw for idle and high. If it idles fine I doubt its the needle. Check the high mixture screw adjustment and for leaks.
 

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multi species angler
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Had a similar issue with a motor a few years ago. It was a needle. Symptoms sound exact.

lund 1775 pro v se
 

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Tap lightly on both carbs with something solid. Sometimes this will break them loose. It is the fuel level needle, not the low or high speed adjustments. Mike
 

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If u can remove a bowl the main jet is #9. Your not pullin fuel out of the bowl though it or your bowl is low because of filter,pump,tank,needle&seat. If you can remove them(bowl),use carb spray and blow the jet out. Some carbs r a pain so if you cant remove the bowl then rebuilding the carbs is the only thing u can do(removal). Just make sure everything else is rights. You might be able to remove bowls and pump bulb to verify flow to needle and seat. These guys r right just got to go in order before you take something apart you don't have 2. Supply line,Filter and pump r first. Pump the primer bulb and note fuel out of the carb lines. Crank and do the same with engine spark disabled. Remember safety first. Gas an spark DONT mix!
 

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Discussion Starter #10
Thank you all for the tips. I appreciate the help. I learn more from this site than anywhere.

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fishing fool
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All info above is good. However, the first thing I would check is to see if you have an in-line fuel filter and maybe it has got a little dirt in it. Had a problem with my "little" Johnson and that was all it was. Could be a lot simplier than the above. Good luck.
 

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Had a similar problem with an older johnson 70hp. I troubleshooted the fuel and spark and still had issues. It ended up being the power pack...around $100 and 5 minutes to install. Motor has run great ever since.
 

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all good idea,s but I,m think a hose collapsed . as you speed up the hose sucks together , this gas we buy now eats up rubber. some times you can feel the hose and as you squeeze it you,ll feel how weak it is. start with the hose from tank in to the pump , before you start taking things apart or turning screws. its a simple problem jut gotta track it down.
 

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Discussion Starter #16
I did buy a new hose and bulb. My old bulb had lots of cracks. If you squeezed it hard enough, I think it would split. Haven't been out yet to check it. Thanks for all the good ideas.

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if your bulb is collapsing then you are starving for fuel. Check your anti-syphon valve, its probably gummed up or check the vent on your fuel tank.

dale
 

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Discussion Starter #18
I think I may have solved my problem. I bought a new fuel hose and bulb, now the engine runs fine. The old bulb was soft and cracked. Thought suction may be collapsing it or the hose as someone suggested. I cut open the old hose to see if it was clogged or anything. Inside I found an inner "bladder" or tube that was a clear plastic or heavy cellophane...maybe the ethanol weakened it? Wasn't rigid at all. The hose and bulb were Bass Pro brand that I bought a couple of years ago. Something to keep in mind. The outer hide seemed find but this inner bladder was as rigid as cellophane, no doubt collapsing in on itself. Thank you all for the advice and pointers. I have attached a photo.

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It is always best to buy oem parts, aftermarket parts do not work as well, especially fuel line parts.
Wives tale.

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