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  1. #1

    Default Spark plugs for a mid-80s Merc XD

    Hello folks,

    First time poster! I recently bought a 16' fishing boat paired with a mid-80s 18HP Mercury XD. The seller believes it is a 1985. I still need to confirm this. But when I googled images of 85 Mercs, they look the same. Motor is idling rough and stalling while in neutral. I am going through the process of diagnosing the problem. I figured I change out the plugs while I am at it (the old ones were fouled) and lower unit oil. I am thinking a carb clean could help. While in forward or reverse, it seems to be okay, although I've only done this in a bucket, not on the lake.

    What are the proper plugs for this motor? The old ones in the motor are NGK BUHW however I cannot find these plugs at my local stores. I looked up plugs that are compatible and one site listed the Champion L77JC4. Will these plugs work?

    Also, what fuel filter (part/number) does this engine take?

    Thanks so much in advance!

  2. #2
    Join Date
    Sep 2010
    Posts
    24,230

    Default Re: Spark plugs for a mid-80s Merc XD

    So it has the copper / bronze colored decals ?-----Start with a compression test.----Post the numbers here.-----And it will need a new water pump impeller.-----Most of those I look at have an impeller that is old and cracked.

  3. #3

    Default Re: Spark plugs for a mid-80s Merc XD

    Quote Originally Posted by racerone View Post
    So it has the copper / bronze colored decals ?-----Start with a compression test.----Post the numbers here.-----And it will need a new water pump impeller.-----Most of those I look at have an impeller that is old and cracked.

    Okay, thanks. It is pumping water pretty nicely... but he told me he hasn't replaced it. I don't think I have the tools to test compression, but I may.. I will look. If i don't I'll get my hands on one. Never done one before - Youtube is my friend I guess. I'll take a pic of the motor. That should confirm vintage.

    As for impeller, i'll need to find a dealer who sells them. Do you know the part number for that impeller?

    Thanks!

  4. #4
    Join Date
    Sep 2010
    Posts
    24,230

    Default Re: Spark plugs for a mid-80s Merc XD

    It needs a new a new impeller !----Find it right here on this site.------" engine diagrams "-----And just a few clicks.

  5. #5

    Default Re: Spark plugs for a mid-80s Merc XD

    https://www.mercurymarine.com/en/ca/.../parts-catalog

    This link will have all the part numbers you’ll need.

    https://www.boats.net/catalog/mercury/outboard/18hp

    If your engine was manufactured for the Canadian market then you’ll have to dig deeper to find the cross reference serial numbers.

  6. #6

    Default Re: Spark plugs for a mid-80s Merc XD

    Quote Originally Posted by William01 View Post
    https://www.mercurymarine.com/en/ca/.../parts-catalog

    This link will have all the part numbers you’ll need.

    https://www.boats.net/catalog/mercury/outboard/18hp

    If your engine was manufactured for the Canadian market then you’ll have to dig deeper to find the cross reference serial numbers.

    I am in Canada - so i assume it was made for the Canadian market...

    Thanks for the info! I'll be back...

  7. #7
    Join Date
    Sep 2010
    Posts
    24,230

    Default Re: Spark plugs for a mid-80s Merc XD

    Does the motor have the copper / bronze decals ?----Canada is fairly big I heard.----Takes me 24 Hrs driving to get out of Ontario if heading west.----If impeller has not been replaced recently you need a new one.-----REASON-----There is no warning system or shutdown feature on these motors.-----It will run until you notice a loss of power.----Then it is big $$$ and beer token repair time.----There is no difference between an American and Canadian marketed motor !!-----
    Last edited by racerone; 06-27-2022 at 10:33 AM.

  8. #8

    Default Re: Spark plugs for a mid-80s Merc XD

    Quote Originally Posted by Splaker View Post
    I am in Canada - so i assume it was made for the Canadian market...

    Thanks for the info! I'll be back...

    https://maxrules.com/models/Merc_model_files/15-25.php

    The above link should help you out

  9. #9

    Default Re: Spark plugs for a mid-80s Merc XD

    Thanks...

  10. #10

    Default Re: Spark plugs for a mid-80s Merc XD

    I found what I think is the serial number but when I input it, I cannot find info on it...

    The number is A701232

  11. #11

    Default Re: Spark plugs for a mid-80s Merc XD

    I did a quick search and all the Canadian serial numbers in and around your year and hp seem to start at 7 million where as the number you provided is 7 hundred thousand. Did you maybe miss a digit?

  12. #12
    Join Date
    May 2015
    Posts
    2,835

    Default Re: Spark plugs for a mid-80s Merc XD

    Here is a service bulletin for those motors regarding spark plugs. It won't let me upload it. Service bulletin 91-36 is the one you need
    Last edited by flyingscott; 06-28-2022 at 12:00 PM.

  13. #13

    Default Re: Spark plugs for a mid-80s Merc XD

    Quote Originally Posted by racerone View Post
    So it has the copper / bronze colored decals ?-----Start with a compression test.----Post the numbers here.-----And it will need a new water pump impeller.-----Most of those I look at have an impeller that is old and cracked.

    Did a compression test just now. 130 and 135... is that good? I think it is...

  14. #14

    Default Re: Spark plugs for a mid-80s Merc XD

    I also changed lower unit oil, spark plugs and fuel filter... sprayed some of that carb gunk out and motor is running quite a lot better...

  15. #15
    Join Date
    Jun 2022
    Location
    Saskatchewan Canada
    Posts
    14

    Default Re: Spark plugs for a mid-80s Merc XD

    I am also enquiring about a Canadian Marketed 75 HP Mercury Mariner.

    Do spark plugs really make that much difference?

    It says for boats MFG in Canada & Belgium to use the NGK BUZHW-2. This is a spark plug with an inductive resistor. I called NGK tech and was told that due to a shortage in tungsten I beleive they were discontinued a year ago. Champion QL78V is supposed to be a replacement maybe.

    Not sure how readily available these are.

    Anyone know what the differences are between Belgium, & Canadian marketed motors over all the others specifying the NGK BUHW-2?

    Yes my SN is A715190

    https://www.marineengine.com/parts/m...7075726/277_40

    https://www.marineengine.com/newpart...um=33-14103570

  16. #16
    Join Date
    Jun 2022
    Location
    Saskatchewan Canada
    Posts
    14

    Default Re: Spark plugs for a mid-80s Merc XD

    What is the actual difference between Canadian engines and all others?

    I am in the same boat.

    Supposed to use the NGK BUZHW-2 with an inductive reducer.

    Spark plug is supposed to be discontinued.

    What is Service bulletin 91-36? I see another person mentioned it.


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