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mid 80's 25 horse merc


huntnfish

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I have a mid 80's 25hp merc that does not run real well at idle. It runs fine at top speed, but when I want to do some trolling at idle, it dies out. There is a knob on the front that is the choke that you turn to choke it. The motor only runs when it is about half choked. I don't really like dinking aroung with the carbs because they always seems to be worse after I have messed with them. Does anyone have any ideas on what the problem could be? Is there any good outboard repair shops in the Fargo-Moorhead area that I could trust to take it to? My dad took his boat in to a dealer for a spring tune up and all they did was run some motor tune up solution through it and it never did help. Now he uses about twice as much gas as he did before and the same amount of oil. That makes me kind of skeptical about bringing mine to a dealership.

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The motor only runs at 1/2 choke on low speeds or all the time?

It's likely a carb prob either way. Time for a good cleaning, or rebuild. I would recommend picking up a service manual for that motor and a rebuild kit and take care of it yourself. Rebuilding carbs on small engines is generally simple, and may be your only solution if you dont have a mechanic around. I'm too far away or I would do it for you.. rebuilding a carb is cheaper than buying a new motor.

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I cant tell you directly this is the problem.. but it sounds to me that your low speed jet is plugged up .. its one of the most common problems with all small engines that arent used constantly.

You basicly need to take that carb apart piece by piece and clean everything out with carb cleaner, and compressed air if possible. Be sure to keep track of where the jets and seats are EXACTLY (example.. 2 1/4 turns out) and you should not have a problem when you get your carb back together. Be sure you can see clearly through every little hole in the jets. The jets get screwed down tight on most carbs, but dont assume until you check. When the carb is off(or on if possible) be sure the butterfly(flap) is opening up all the way when the choke is off, and closing all the way when its open ... it not impossible for the choke to be malfunctioning and causing many, or possibly all of your problems.

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I have a 88 Merc 25H. Mine does that too. I do think I need to have my carb rebuilt. I've cleaned the he!! outa it and still does it. My shifter and throttle are on the handle. So I turn it and it goes into gear, turn it more to give her gas. Do you have that same kind of model?

I also have my top cylinder that doesn't burn the gas up like it should. Continues to get gunk built up on the top spark plug. Bottom one seems fine. (I run it 50:1 and sometimes leaner)- no clue on that one.

My Merc also squeals when she runs for a bit. Berings or something (Still can't figure out how to take the lower unit off) Some hidden bolt foils my plans.

Enough about my crap merc, now if you have the simular type with the throttle on the handle there is an adjustable throttle rod that you can "pop out" twist to make it have more gas. (Shorten the length by twisting) But don't twist too far or when you start it it will idle really fast. Facing behind the motor take off the cover and it's located on the right. This is if you have the same type otherwise, good luck.

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Thanks for the reply, Dave. The motor seems to run fine at speeds above idle. I have to keep the choke knob at around half way all the time. It doesn't want to run for more than a few seconds if I am trying to put along. It seems to really load up when idling along. After it dies, it seems to start a lot harder. I will check on the manual and the rebuild kit. Thanks for the reply.

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Yes, my motor is the kind that shifts into gear when you turn the throttle. I don't really want to make any adjustments like you stated because the motor should idle down slow enough for some back trolling. It will be something to keep in mind if the other options don't help. I sure would like to use it for trolling, though. Thanks for the replys.

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I had a similar problem on a ten horse. It was suckin air. I thought the head was leaking, but luckily decided to replace the gas hose and check the connections first. That did it for me.

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Huntnfish,
On my throttle rod thing there's a plastic piece connector that was cracked causing it to slip. I used elec tape and it seems to be fine now, well except for all the other issues.

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if you have chocke half close, its because the engine is not getting enough gas,a-low idle ports,jets pluuged, b- sucking air,closing the choke enrichens the mixter. if u move the jets, count the number of turns in,clockwise, till it bottoms out. easier to get back to same seting. try moving the jet one turn in or out, then put back, if works, thne u have a clean job to do. u have buddies gas tank to hook up and try for air leak, check hoses from hook up to carb also. as for the fouling cyl., did u check the compression? the lower unit has a bearing behind the prop that i was told requires a puller to allow the unit to come off. hopes this helps

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  • 'we have more fun' FishingMN Creators

I concur... smile.gif Sounds like a dirty low speed jet or need of low speed adjustment.

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