HELP just bought outboard

dinghy3000

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Nov 27, 2014
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Hello,

I have recently purchased a 70-78 mercury 200 20hp 2-stroke outboard. Not too sure of the year, the previous owner claims it was a 78, but I don't know if its correct or not. There are 2 serial numbers on the plate. 1 is barely visible, the other is 7044868. Nothing seems to come up when I look it up. It does have the blue stripes though.

Anyway, tried to get it going but it seems to quit out on me. The only way I can keep it going is if I pull the choke out for a split second and then push it back in with the throttle partially open. Revved it up manually by pulling the linkage, revs up a bit and then bogs right out. The throttle twist and linkages all seem to have a bit of play too.

What do you suppose I should look into next?

Thanks.
 

bilge rat jim

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Jun 28, 2012
Messages
330
Your outboard is a 1975 (Canadian serial number- assembled in Canada). I would start with a compression test, remove and clean the carb, and replace the fuel pump diaphragms.
 

Star

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Sep 21, 2010
Messages
481
Yes that will cover you but there are probably factory service manuals that you can download for free. The manuals that you refer to are quite general and are not as good as real manuals. Your problem is very common and will probably be due to old gas residue clogging the idle circuit in the carb. This is best cured by a three or four hour soak in Berryman's chemical carb cleaner (Walmart) Then blow all passages with a $3.00 can of spray cleaner. ALWAYS REMOVE ANY RUBBER OR PLASTIC PARTS BEFORE THE SOAK!!!!!
 

dinghy3000

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Nov 27, 2014
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I recently called the mercury classic hotline, and they then told me to call their publications department. called them asking for a service manual and they said that the 1975-1978 manual was all they had for that outboard. I asked if they had anything model specific, and she said only for the newer stuff. so, I'll probably be ordering one of those manuals. unless you can direct me to one online (I've already looked for hours).

so, living in canada unfortunately we cannot get our hands on any of the berrymans chem dip that you speak of. fortunately, living about an hour away from the border I was able to cross and pick myself up a can for about 19 bucks. went to harbour freight while I was at it and picked up a compression tester as well





so, after getting the outboard onto the makeshift stand I built






I started to have a better look.
couple things I noticed that I had some questions about.

first off I noticed that the ground wire connected between the silver box and frame were rotted out in 2 different places.






next thing I noticed was the inlet male fuel fitting only hand 1 mounting bolt holding it down. the whole fitting was able to pivot side to side.





could that broken wire be a cause of why it keeps quitting?

do I need 2 bolts in there or is it fine to run with just 1 (it might help with the connecting and disconnecting of the fuel line)

when you say soaked in the berrymans, did you want me to to completely disassemble the carb and put all nonrubber/plastic pieces in it? or just unbolt it from the outboard and soaked as a whole (minus the rubber/plastic pieces)?

the directions on the can say to rinse with water after soaking, should I follow that or should I just skip to using air?

compressed air work too? or does it have to be the spray can air?

can I re-use all the pieces in the carb or do I need to buy a new carb kit?

do you set the choke off and throttle wide open when doing the compression test? do you have to disable the fuel somehow?

do you have any instructions on how to set that carb up properly?

sorry for all the questions. I'm fairly new to boating scene, and want to do everything properly. do not want to get stranded out in the middle of no where.

thanks for the help, and I will try to contribute as much as I can.
 

Star

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Sep 21, 2010
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481
I would get another bolt for the fuel connection at some point. Yes remove all plastic an rubber parts (disassemble) leaving choke and throttle plates intact. The chem dip is caustic so you wash it with water to dilute it and then rinse it and all passages with a solvent based spray carb cleaner. Air is good but I like to flush with solvent. The only adjust you have is an idle mixture screw 1 1/2 turns out from a very light bottom, too much force may notch the needle. Throttle and chock open to do compression. Compression should be done on a warm engine. If it has sat for a long time, pull plugs and squirt some light oil in each cylinder. I turn the engine so the cylinders are vertical and gig each cylinder with marvel mystery oil to free up the rings over night. Good Luck!!!
 

racerone

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Dec 28, 2013
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Throttle does not need to be open for compression test on a 2 stroke motor !!
 

Star

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Sep 21, 2010
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481
OK racerone, I learned something today. If I am trying to pack a cylinder with air why not have less restriction of flow. Why would a two cycle be different than a four?
 

racerone

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Dec 28, 2013
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Simple ,---- when the piston comes up in the cylinder the intake and exhaust ports are wide open.-The intake ports are closed first by the piston.---The exhaust ports are still open to atmosphere.---Cylinder pressure is now the same as atmosphere !---As piston moves up the exhaust ports are closed off and compression starts.----Just not the same as a 4 stroke engine !!
 

dinghy3000

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Nov 27, 2014
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well got the compression test done. with or without a squirt of oil and the choke closed/throttle closed the top was hovering around 79psi and the bottom cylinder was hovering around 76 psi.
what do you guys think about those numbers?
also here are the spark plugs.. not much of a gap if you ask me but they were a bit wet I'd say when I pulled them.
how do you guys think they look?



 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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get her started, then check. 79 and 76 sound low.
 

chrome dome

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Sep 24, 2010
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it does sound low,
also, those spark plugs are surface gap plugs, they're different to the standard gap spark plugs,
there is no gap to adjust..
 

dinghy3000

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Nov 27, 2014
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oh no wonder, i thought they were maybe worn out but when i got the ground wire fixed, I checked both plugs for spark, and thankfully they did. I haven't had a chance to do another compression test when warm because I started to work on the carb. I have it unbolted from the block and was only able to find 2 adjusting screws.

which one is the idle mix screw?
what is the other one?





thanks for the input guys, greatly appreciated.
 

racerone

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Dec 28, 2013
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The first picture shows the idle mixture screw.----There are no other mixture adjustments on that carburetor !!!!!!
 

quicktach

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Aug 24, 2012
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394
engine starving. for starters - check fuel system up to carb. service carb. link & sync.
 

dinghy3000

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Nov 27, 2014
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I will dis assemble the carb and soak when I get a chance. you know it's strange the tank he gave me came with a really long line (able to run tank up to bow of 14 ft boat) and gas that's who knows how old. when I press the bulb it doesn't really get hard or firm. when I also depress the fuel fitting and pump the bulb only a splash here and there comes out but I can hear it gurgling back and forth.

I will get a new tank and fittings/bulb and see how that goes altogether

what do you mean by link and sync the carb? hook it all up back together and adjust the idle mixture screw accordinghy?
 
Last edited:

seanymphmike

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Nov 20, 2012
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The male fuel connector only has one bolt on that model. The hole on the other side fits over a lug. It won't take two bolts.
 

dinghy3000

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Nov 27, 2014
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well got the carb cleaned and all put back together. pulled to start and it didn't even want the choke on. idled out smooth. high and low idle seems fine doesn't want to stall out. yeah the fuel fitting is held on by 1 bolt lol the other hole has like plastic mold or epoxy filled in it. re did the compression test after it warmed up a bit, and the numbers were lower than before? they were around the 70 psi mark. doesn't make sense. seems to run pretty good and strong other than smoking a bit. next I'll probably do a gear oil change.

thanks for all your help, greatly appreciated I will try and contribute as much as I can. here are a couple vids I made of the outboard running.

View My Video
View My Video
 
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