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18hp Mercury Newbie

C

cbmercury

New member
Just got this motor yesterday

Just got this motor yesterday and I need some advice. I was really after the boat since I already have a great little Merc 9.8 but am always interested in going faster !

1. Need to know if the Seloc manual is worth the money for minor maintenance and repair

2. Noticed that there is oil pooled up on the heads just below each plug. can't tell what kind of oil. when i remove the plugs they seem pretty oily as well

3. Does some coughing a sputtering but played with the screws on the carb and it seemed to help. the screw on the left is bottomed out and when you turn it counter clockwise it really runs rough

4. Need the oil/fuel ratio

5. Is this a pretty solid motor worth putting some money into ?

6. going to get new plugs just not sure which ones. any help on that would be appreciated

7. is there no kill switch for this motor ? i'm choking it to stop it.

8. noticed that the carb throat is exposed. is there nothing the keeps debris from entering the carb ?

I'm running out to purchase a compression tester to see what shape the cylinders are in.
I believe it's 1980 or 1981 serial number begins with 590

your help and suggestions are appreciated
 
"Hi Charlie,

I'm prett

"Hi Charlie,

I'm pretty much a newbie myself, but here are a few points on which I might venture a comment:

>4. Need the oil/fuel ratio

I would assume it's the usual 50:1 - resident experts, please advise if otherwise.

>5. Is this a pretty solid motor worth putting some money into ?

That would probably depend entirely on the condition of the individual engine; how it's been looked after and run (or not, as the case may be); and what your definition of "some money" is.
happy.gif


From what I've gathered, a well-maintained and run outboard will last almost indefinitely, but you are looking at an engine here that's almost 30 years old. Probably around that number you start crossing the fine line into antique outboard restoration, which sounds like a fantastic hobby, but in which the financial and time investment of getting the motor into working order starts to grow exponentially.

But on the other hand, I know people run engines much older than that in daily use all the time, so once more - it depends.

Again, I am new at all this myself, so hopefully the gurus can add a few words of wisdom here.

>7. is there no kill switch for this motor ? i'm choking it to stop it.

At least newer model years of the 18hp have the stop pushbutton at the end of the steering handle, is it not there?

>8. noticed that the carb throat is exposed. is there nothing the keeps debris from entering the carb ?

AFAIK, this is normal - if you run the engine in normal fashion with the cowl on, I wouldn't expect any problems with getting junk sucked into the carb."
 
"fuel ratio is 50:1, oil in pl

"fuel ratio is 50:1, oil in plugs may be from previous owner who has winterised engine, two strokes only lubricate bores from oil in fuel, if the engine is not going to be used for long periods it is advisable to put a smalls amount of oil into the pots to resist rust and other electrolytes eating into the precious cylinder.

With your screw adjustment if it is all the way in it will stall engine cause that is an air idle mixture screw, it should be 2-2.5 turns out anti clockwise from fully clockwise in, if it still plays up and stalls the carb might be gunked up and the air idle jet may be blocked.

As far as plugs go i need either serial numberor take the serial number to nearest merc dealer and they will tell u recommended plugs.
As far as the seloc manual for it i wouldnt waste the 40+ bucks, u can get complete merc engine manuals on CD off ebay for around 5 bucks posted, One CD will cover most models from 2.5hp to 225hp engines all years and types they are in adobe format so u can zoom and even print articles relevsant to which part u are working on. very handy as u dont have to dirty a good copied book... I have one!!"
 
"Tom,

Thanks for the info.

"Tom,

Thanks for the info. I found the kill switch this morning after reading your reply.

I checked the compression last night and both cylinders show 100psi so i'm feeling a little more confident about this motor

thanks for your help !"
 
"Brent,

I'll go with th

"Brent,

I'll go with the 50:1 ratio. I asked the guy who owned the boat and he said 6:1 maybe that's why the motor runs rough - he also told me it was 90s model. Once again I was really after the boat - the motor just a bonus

the serial number is 5905581

there are two screws on the face of the carb which one does what and what are the general turns for each ?

I found a cd based manual - it should be arriving early next week.

thanks for the help I really appreciate it !"
 
">6:1 maybe that's why

">6:1 maybe that's why the motor runs rough

Good grief - I wonder whether that might have anything to do with the oil-covered plugs.
wink.gif


Based on your serial number, you can find parts listings and diagrams for your engine here or at other similar vendors: http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=90649

You can then use the numbers to order the parts you need from your Merc dealer or preferred online supplier. I've found having the exact OEM numbers makes life helluva lot easier when you're shopping for parts that the local boat shop will likely need to order in.

Unfortunately I'm not familiar with your particular carb, but according to the parts diagram, at least the screw at 2 o'clock from the intake (part number 3 under Carburetor in the above link) is the idle mixture screw. Not sure what the other screw might be? For general instructions how to set the idle mix, see our thread here: http://www.marineengine.com/discus/messages/12479/193130.shtml

At least your compression sounds good, so hope it works out with the motor. Happy boating!"
 
"dont mess with the air idle m

"dont mess with the air idle mixture screw until u have removed all the 6:1 fuel and cleaned or replaced the spark plugs, once u are running the correct fuel ratio it may eleviate the rough running."
 
"Tom,

Do you know of other

"Tom,

Do you know of other on-line stores that may have discontinued parts for this motor ? Any body in this forum ?

thanks"
 
"Charlie, if you are looking f

"Charlie, if you are looking for "new" "oem merc" parts, www.mercruiserparts.com is probably the best on the net. If you don't mind using Sierra parts, Andrew who runs this site sells parts and his prices are outstanding - just Sierra doesn't always carry everything you might be looking for.

Alternately, you can check the various listings/stores on Ebay. I have purchased numerous OEM part there from various sellers and have not had any issues..."
 
"thanks for the info Graham.

"thanks for the info Graham. I don't see a lot of discussion on this particular motor and am wondering if parts and support will be limited. It's an 80-81 18HP Merc serial number starts with 590. Is this motor of the same family as the 15,20, or 25 ?

thanks"
 
"Charlie, yes, the 18 is simpl

"Charlie, yes, the 18 is simply a detuned version of the much more popular 25 - only the carb is different.

Merc still carries a fair number of parts for these motors and the ignition system in particular was also used on the 6/8/9.9/15 horse series which was in production all the way up to 2005 - so very much available.

The 18/25's were introduced in the 1980 model year - your serial makes it one of the originals produced in late 80 or early 81.

After the 1985 model year, Merc discontinued the 18 horse. They turned it into a 20 as the sister motor to the 25 horse. All the 18's, 20's and 25's shared the 24.8 cu in powerhead and all have Merc's Thunderbolt 4 ignition, which as I stated was used on the small 2 stroke Merc's until they were totally discontinued.

An excellent little motor that you should be able to easily maintain for years to come..."
 
Makes me feel a little better

Makes me feel a little better about this motor.

So when I can't find a particular part i'm looking for how could i find out it the 20hp or 25hp version of that part will work for my 18hp?


I was considering cleaning/rebuilding carb but can't locate the gasket/seal kit for it - says no longer available. Also noticed no lower unit gasket or seal avail and i guess i need that for replacing the impeller correct or do i access the impeller via the water inlet screen ?

Should have the manual for this by friday so i won't have so many questions !

thanks
 
"Charlie, yes, it has an old s

"Charlie, yes, it has an old style carb (back draft I believe). And while the entire powerhead gasket set is no longer available, I still see an active listing for the carb repair kit (1399-8153) and the close to the same, fuel pump kit (1399-8154) which sell for about 40 and 20 bucks respectively.

The lower unit seals are discontinued, but there is a complete waterpump kit (46-99157T2) for just over 70 bucks that includes the seals for below the waterpump base. The lower seal kit would include the portion required for the propshaft.

The impeller (47-8M0024502), about 20 bucks, is accessed by dropping the lower unit and removing the pump cover which slides down the driveshaft.

Unless you have a leak in the propshaft, you can get by without a lower seal kit. Often times, simply replacing the impeller and perhaps the waterpump cover gasket is sufficient...

If you are ever in need of a discontinued part that can not be jury rigged/fitted with a newer part, you can get ahold of the guy at www.oldmercs.com - if he doesn't have what you are after, can often times point you in the direction of where to find it.

I have found that a significant number of discontinued parts on the small mercs only have a slight modification on the new part number and the new part will often fit with a very minor modification (redrill a hole etc). Merc isn't too quick to let you know this. But it's a part by part basis comparison at the time to figure if it will work or not..."
 
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