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Roscoe16

Mercury 40HP Misses At Full Throttle

14 posts in this topic

I have a 1993 40HP Mercury. Took it out for opener this past weekend and found it misses at full throttle. If I ease off some it runs fine, also seems to run fine idling and at slow speeds. I changed gas tanks and no difference. Anyone have any ideas?

Thanks, Roscoe16

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Is it missing or dying out? If dying out check to see if the gas bulb stays hard when you're running. If it is getting soft replace the whole hose. It sounds like you might have a small air leak. I have had to do that a couple of times in the past ten years. It is a cheap first thing to check.

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If its missing I'll bet its water. Check this thread out

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It's missing, not dying out. The bulb on the gas hose is hard. I tried a tank of fresh gas in it and it is doing the same thing. I changed the fuel filter last year. Fuel pump going bad? Stator? Bad spark plug?

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Sounds like a fuel supply issue. When was the last time the carb(s) were cleaned?

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What color stator does that motor have? Around the early to late 90s Mercury had a terrible time with the black stators and did a recall and went to a red stator. Most of the problems were in the higher RPMs

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You must be using portable gas tanks?

New spark plugs isn't a bad idea.

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Do like Emeril does and kick it up a notch. BAM! Add some SeaFoam motor tune to your gas tank. This stuff can cure a multitude of ills! Good luck! grin.gif 1DIRTBALL wink.gif

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Got her fixed yet? You have to determine if you have a lean miss or an ignition miss and then find the specific cause. Is this a 2,3, or 4 cylinder 40?

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Thanks for all the info guys. Have not gotten it fixed yet. I have not had an opportunity to try any of these ideas yet. It is a 4 cylinder. I had the stator replaced about 6 years ago, not sure what color the new one is.

Roscoe16

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OK guys, I changed the plugs, checked the gas in a glass jar (looked OK), changed the fuel filter, put a can of Seafoam in the gas and ran a tank and half of it and it is no better, actually might be worse, seems to miss a little when I first accelerate, then is ok to full throttle then misses a lot at full throttle. If I back off a hair it runs fine. It has the red stator. Time to take it in?

Roscoe16

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sounds similar to my problem i have a 2002 40hp merc but mine was okay at low end up till about 3/4 throttle and it bogged bad, end result after 2 trips was there was "dirt" in the carbs mine a 3 cylinder 2 stroke may need to bring it in unless you know how to clean them

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I know someone who had the same problem. He replaced the plugs and hose and still missed on him. He finally took it in and they said the gas they make now at some places is cheaply made and gums up the carb. He got his cleaned and works great. If you have a Shell gas station Id try it. I seen on tv they put something in there gas that doesnt gum the carb.

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Its a process of elimination. If your sure there isn't any water in the gas, the fuel lines are good, all connections are good, the filter and plugs have been replaced, then I'd clean and rebuild the fuel pump and carbs. I'd be doing that myself so if it wasn't the problem I'm not out anything but I'd know that its been done and something I won't have to do later. Next step would be to take out the manual and start checking the electrical end or a trip to the service department.

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