Mercury 18XD or 25XD Starting Problems

Imawoman

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Jun 28, 2010
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I'm not sure exactly what HP the Mercury outboard I have. On one side of the lower unit it has 18XD and on the other side it has 25XD. It's older probably either a 1985 or 1987. Not sure of that either. I purchased it with a 1970 aluminum Orlando Clipper 14' boat. The previous owner didn't use the boat very often. Maybe once a year. I've had new spark plugs put in & have had it checked over (compression etc) and the boat dealer said it's in great condition. I've also replaced the fuel tank hose & fittings. I took it fishing Sat and the motor started right up & it ran great. Yesterday "nothing". After flooding it and letting it sit for about 1/2 hr it finally started & ran great. It had rained the night before. Could dampness cause a problem? It has 2 plastic 3 gal fuel tanks that I'm sure are rather old. I've added gas to them with oil & stabil. Could dirt etc sitting on the bottom of the tank cause it to not start? Also the previous owner used that spray (quick start???) to start it. I don't want to have to use that but if he used it could that be some of the problem?
 

will941s

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Re: Mercury 18XD or 25XD Starting Problems

You should probably replace the gas tanks with a 6 gallon, as well as the lines from the gas tank to the motor and the lines on the motor its self. Also wouldnt hurt to rebuild the carb, and clean out the internal components with carb cleaner and compressed air, and changs the plugs. Fresh gas, new lines and a clean carb go a long way with these motors. Never use quick start with a 2-stroke OB. If you have to use something, use a mix of oil and gas in a spray bottle. The correct starting procedure is to pull the choke all the way out (sprays the primer) and push it back in one click (full choke), 2 clicks (half choke) or all the way back in (no choke) before you attempt to start the motor. Also can you post the serial number so you can get the correct model and year?
 

will941s

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Messages
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Re: Mercury 18XD or 25XD Starting Problems

Dampness should'nt effect it too much. I read where you replaced the tank to motor lines and the plugs. So just rebuild and clean the carb, replace the tank and replace the lines on the motor. Also run some seafoam after you rebuild the carb.
 
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Imawoman

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Re: Mercury 18XD or 25XD Starting Problems

Hi and thanks for your help! I just had a mobile marine mechanic come over and he said these older Mercury motors are known for build up in the carburators. He's going to work on the carb, check everything out, lines etc etc, empty my gas tanks & clean them out so I can start fresh. In this boat there's not enough room by the motor or a 6 gal fuel tank. As far as the choke, it's broken. It comes completely out of the hole and is missing a piece. He also said once the carbs clean the only thing I should add to the gas is oil & that ethyenol treatment. The serial number (which was worn) I believe is 6470750.

thanks again!
 

will941s

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Re: Mercury 18XD or 25XD Starting Problems

No problem. I don't have the vast resources as some people on here but I believe your motor is a 1984 but I can't tell whether is a 18 or 25hp. The serial numbers for both are pretty close. Parts for the two motors are the same though. When you get the boat back, as long as you keep fresh gas and treatment in the tank you should be ok. I have two 25's (89' & 98') and both of them have a water fuel separator kit, and that saves me TON on carburator problems, not to mention it's takes alot of the headache out of the ethanol in the gas. You can get the kit from wal-mart in the marine section for around $30, and install it in no time. Very good motor though, keep it serviced and you will get years of use out of it.
 

Imawoman

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Re: Mercury 18XD or 25XD Starting Problems

Here's the woman again trying to get this crazy mercury running so I can use the boat. I have fished & had boats all my life but never problems like this. I had the carburator cleaned (it was dirty). Took the boat out & the mechanic had the idle set too high so he fixed that (I thought). He also said the choke was broken which I knew about so I order the parts & they came in today. Last weekend (because he showed me how to take the hood off & choke it) I tried that for an hour or so and nothing. So now I think he has the idle set too low. My two questions are: I know where the idle control is. Is there a certain way (so many turns?) that it needs to be set? The other question is on this motor the choke (square thing) I think they call it an actuator/primer comes with a knob and a tiny "o" ring is that a biggie to replace? The one that is broken is broken at the back, has no knob & is not triggering the choke. Can a woman do it since I haven't heard from my mechanic?

thanks for your help!
 

will941s

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Re: Mercury 18XD or 25XD Starting Problems

LOL...no reason at all that a woman can't do this. Heres what you need to know and do. The square thing is the primer....and you need the choke assembly to use it. Get the choke assembly, there is a small nipple on the bottom of the carb that fits into a small hole on the bottom of the choke assembly, then it screws to the face of the carb to hold it in place. To start the motor after you squeeze the primer ball til it's hard, you pull the choke all the way out once (primes the intake), then push it in one click (for full choke), two clicks (for half choke), or all the way back in (no choke), to start the motor. If you pull it all the way out more than once, you will flood the motor. And keep in mind if it's warm weather, you may not need the choke at all.

Mechanical stuff: For both of these procedures, back the boat in the water and leave it secured to the trailer.

If the idle it's self is set too low, heres how to tell. In the water, start the motor with the hood off. Your looking back at the motor at the face of the carb. On the left side is the butterfly lever. Open that lever slightly to see if it will maintain idle in neutral. If it does, and you can hold it open to a point that it's not idled too high and it stays running; look at the rod that attatches to the mechanism that opens the butterly. The end of the rod that attatches to the carb has adjustable ends. Pop that end off with a flathead screw driver and adjust it slightly and pop it back on til you get that idle. Once you get the idle you want in neutral, the put it in gear and see if it will maintain. Keep adjusting it til you get what you want in gear and in neutral.

Carb out of adjustment. In the water, start the motor; put it in gear. Looking at the face of the carb, on the top/front you will see the idle set screw. With it running and in gear, take a flathead screwdriver and adjust the screw with VERY small movements at a time, and leave about 10-15 seconds between adjustments for the carb to react. Turn it clockwise (lean) til it begins to die. Then begin to turn it counterclockwise (rich) til it begins to die. From that point turn it about 1/8th to 1/4 of a turn back clockwise til it levels out and stays at idle. You want it on the rich side of that "majic" position. After you do this, hit the has a few times, let off a few times, let it sit in neutral, gear, gas etc. to put it through the paces and to make sure no more adjustments are in order.

Easy to do, and doing it yourself will save you tons. Just remember, with any adjustment like that it HAS to be in water. Keep us posted on the outcome. Good luck.
 

will941s

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Oct 1, 2007
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Re: Mercury 18XD or 25XD Starting Problems

And the primer: Take off the carb, two nuts, one one each side of the carb. Looking at the primer, is 4 screws in top; remove them. Take off the top of the primer CAREFULLY, theres a spring in there. Slowly lift the top of the primer off, remove the diaphram and replace it. Make sure the spring and the small ball bearing in the bottom of the primer bowl are still in place. The O-ring snaps on the top of the primer, the diaphram plunger runs through the little hole in the o-ring. Once the new O-ring is in place, the diaphram is in place, then place the top of the primer back on the primer bowl, replace the screws, and put the carb back on. Get to boating.
 
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