Mercury Classic 50 problem

k5blazerboy · Apr 6, 2011

So, I just bought a classic 50, ran great on the guys stand (cowl off), got it home, mounted it, and found with the cowl on it will idle for a few seconds and then die (as though its starving itself for air) Bottom carb leaks, so i'm thinking a carb rebuild is the solution? 123 psi on all 4 cylinders, as well as spark on all 4. And again, it idles great cowl off. (just the tin part) Don't wanna spend a fortune at the marina, if a carb job will fix it, and I am missing out on the best walleye fishing of the year!!! Thanks guys!!!

Oh yeah, and it leaks fuel on priming, I am really thinking carbs!!! Hopefully one of the 4 mercury shops in town has a rebuild kit.

k5blazerboy · Apr 7, 2011

Re: Mercury Classic 50 problem

K guys, so I rebuilt the cars and no more leaking, bulb stays hard!!! BUT Motor will now idle for a minute or 2 then die, which is an upgrade. Also doesnt plane out real good........so a fule problem perhaps....going to the shop tomorrow if I I cant find any help.........thanks guys!

carholme · Apr 7, 2011

Re: Mercury Classic 50 problem

k5;

Have you tried to keep the engine running by constantly squeezing the primer bulb when it is starting to die? If it does keep running but quits when you stop squeezing, the fuel pump becomes suspect.

What /sn do you have?

Gerry

k5blazerboy · Apr 7, 2011

Re: Mercury Classic 50 problem

Yea it was tried. It is uncertain if that made any real big difference in performance. Not sure off hand about the serial number. Would have too look in the morning. Might end up just taking to the shop. I'm not real sure where to start. My 3 ideas are carb adjustment, fuel pump, or head gasket. Sound right or no?

1946Zephyr · Apr 8, 2011

Re: Mercury Classic 50 problem

Most mercs don't have head gaskets. The heads aren't detachable. They typically have a "water jacket cover" What year is this Merc? If you're getting 123 psi on all cylinders, then you're fine.

CharlieB · Apr 8, 2011

Re: Mercury Classic 50 problem

You mentioned that the motor runs with the cover OFF, does this mean it runs different with the tin cover ON?

If so, two common faults, first is a spark plug wire cracked/aged, shorting and grounding spark, killing one or more cyls.

Second is leaking exhaust, fumes could be drawn back into the carbs, causing the mixture to seem overly rich due to the lack of air, choking and killing the motor.

k5blazerboy · Apr 11, 2011

Re: Mercury Classic 50 problem

CharlieB said:
You mentioned that the motor runs with the cover OFF, does this mean it runs different with the tin cover ON?

If so, two common faults, first is a spark plug wire cracked/aged, shorting and grounding spark, killing one or more cyls.

Second is leaking exhaust, fumes could be drawn back into the carbs, causing the mixture to seem overly rich due to the lack of air, choking and killing the motor.

You would be correct! Took it to the shop, 40$ to diagnose it. Bad CDI, firing on only 2 cylinders. So I believe this is the part number:#CDI114-5772..................tey want 250 for a new one, 550 to put it in or they have a used one for 140 440 to put it in. I told them I will do it myself at that price. Anyway, anyone know where a guy could get one quick and used?

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=220616965808&ssPageName=STRK:MEWAX:IT

That one correct?

CharlieB · Apr 11, 2011

Re: Mercury Classic 50 problem

That should be the correct switchbox.

You might want to verify that it is the switchbox and not the trigger.

Swap the trigger leads to see if spark switches to the other cyl's.

Do NOT attempt to start the motor, just test spark.

CDIElectronics has a great, FREE, downloadable Ignition Troubleshooting Guide that literally spells out how to troublshoot and test your ignition to determine what is wrong.

Since there is NO RETURN on electrical parts, it would be a good idea to be SURE you are getting the part you need without buying unnecessary parts.

k5blazerboy · Apr 22, 2011

Re: Mercury Classic 50 problem

Got the switchboard installed. No longer need ether to start it, still won't idle more than a couple minutes. Weather has kept me from testing yet. Idling issue still irks me, my 73 evinrude would idle all day.

CharlieB · Apr 23, 2011

Re: Mercury Classic 50 problem

k5blazerboy said:
ideas are carb adjustment, fuel pump,

Stick with your oroiginal plan, clean the carbs, rebuild the fuel pump, link-n-sync per the manual

You're gonna like yer Merc!

k5blazerboy · Apr 23, 2011

Re: Mercury Classic 50 problem

Played with the carbs, running smoother, less smoke. Still not running the best sealed up...................BUT we did find the GASKET-TRANSFER PORT COVER 27-279361 to be leaking very very bad. Ordered the new one, as no shop had one. But, we are thinking these exhaust gasses are choking off the motor from fresh air when the thing is sealed up tight. Agreed?

CharlieB · Apr 23, 2011

Re: Mercury Classic 50 problem

That leaky gasket will cause a problem, it allows fuel/air to leak, making for a reduced power charge to that cyl ANDcauses the fresh air intake to the carbs to go rich with fuel, essentially trying to flood the motor.

Replace the gasket, yes.

But I still recommend you clean the carbs and rebuild the fuel pump as you want to reduce the possibility of any future problems that could damage your motor.

k5blazerboy · Apr 27, 2011

Re: Mercury Classic 50 problem

Ok, everything we came up with is now fixed, and now it's running super super rich. Tried to find a mercury manual on ebay with no luck. Wondering where to start with the carbs? No matter what we did it was rich. And if it idles for a few minutes (which it finally does), and I turn it off and try to start it right away I need to turn the idle lever all the way up and it fires right up. HELP!!! HA! You have been a great help by the way and it's very appreciated.

k5blazerboy · Apr 28, 2011

Re: Mercury Classic 50 problem

Well good news and some really really really bad news I think............so I found online where to start with carb adjustments, had it running fairly good, got a little crazy on the throttle in the barrel and water came up. Seemed like it was fine, turned it off within a minute of that, sat down for a bit to see if it would fire back up and there is nothing, just choke. So what did I fry? I attached a picture of what i'm assuming was the fuse link wires. I have a rock in my stomach right now knowing that I should have noticed that the fuse block was hacked. I cant believe this, I was almost there :facepalm:

UPDATE: Cranks when starter solenoid is jumped. It is for sure in neutral, and the safety switch is in its correct position.

UPDATE 2: Followed the directions on this page HOW TO: Troubleshooting your engines starting system...............didn't help. I am at a complete loss on what to do at this point.

Update 3: Removed control box, went through all the wiring, everything but the neutral safety checked out. Ignition switch was brand new yesterday, so I would think that is not the culprit (unless something fried it)

k5blazerboy · May 3, 2011

Re: Mercury Classic 50 problem

Just an update to anyone interested. Fixed the boat last friday. It was a broken neutral safety switch causing the problem. I added a main fuse to the block, got it running real good and headed for the lake. While on the lake it ran great! Only fail.........spun a prop hub, so it took roughly 1.5 hours to get back to the launch, went to my marina the next day, he sold me a prop for 20$ to get me going, and said 45$ to fix the hub. All in all i'm happy with the motor, seems like a gas hog, but it maybe the prop hub that caused that (it seemed like it was revving out when it shouldn't have been). But I also ran about 10 miles with 6 gallons of gas, 3 people pushing my 16' starcraft 12 degree prop. I now have a 10 degree on it, and will be testing in tomorrow. Thanks for the help guys, bought this motor and got it running for around $800......so more than I would have liked to spend, but what do you do. My next motor on my next boat will definitely be bought from a dealership, it will be 4 stroke, it will be at least '05 and it will be a merc!

k5blazerboy · May 4, 2011

Re: Mercury Classic 50 problem

Another update/help question. Was going real fine in a slow no wake area, went to put the motor in reverse.........nothing, forward................nothing. I took the lower unit off and two small black circles with splines inside fell out with it, they were just laying there. When at the launch in forward in spun one way, neutral both ways, and unfortunately in reverse it spun both ways as well. Junk gear housing? hope not. Really need some help quick please guys. Wish I could but ya'll a beer after this!

ChefMercury · Feb 20, 2019

How did all this turn out? Was your lower unit shot? I know a guy that is having the same initial issues that you had with yours. It runs great with the cowel off but dies when the cover is on. Carbs have just been rebuilt. He is claiming that it is leaking around some of the bolts. I am trying to get a location of what exact bolts he is referring to. Sounds like it could be the issue of it sucking in fumes when the cover is on it. Wondering if anyone else has had issues similar to this as well.

Mercury Classic 50 problem

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