80's merc classic 50 trouble

[microvibe]

I have a mid 80's merc classic 50, it has the dual carb with feul pumps built into the side of carbs. With cpl guys and gear in boat i can get it to 4600rpm at 3/4 throttle if i go to wide open throttle the rpm's drop to about 4000 and it acts like a rev limiter in a car where it doesnt surge but just holds that rpm. If i try to tow a kid on a tube i am lucky if i can get over 3500 rpm at 3/4 throttle and wide open is even worse. Feul lines are all new switchbox and coils are new. There is only one visable problem the top carb where the feul pump and carb meet is wet as if it leaks it doesnt leak so that its driping but it stays wet would this cause such a drastic problem and why only at wide open and not 3/4. I have tried priming bulb while wide open makes no difference.

Any ideas on where to start trouble shooting, i'll probably make a service apointment but there so backlogged so i figured i might be able to just do it myself.Also the serial number on the tag is a132588, i cant seem to find what year it is i was told 1988 but on merc site if i put in that serial it adds a 0 in front of the A and gives me a model number that relates to a 1985.

thanks

 

[jebeebe]

Re: 80's merc classic 50 trouble

sounds like it is sucking air ,maybe where the fuel pump is wet. I am not familiar with that pump on the carbs. My 60 has the pump on the side of the block. It could also be timing as when you advance the throtle the trigger advances the timing. At wide open throttle it could be too far advanced causing it to loose rpms. If so a "link and sink" procedure might be in order. I would check the gasket on the pump first..........Jerry

ps..If it is timing, I wouldn't run it too long that way as it will eat up pistons.

 

[microvibe]

Re: 80's merc classic 50 trouble

Is there anyway to check the trigger timing visually? also what specs and which wires do i test for resistance on the stator trigger coils and switch box.

thanks

 

[sailingwest]

Re: 80's merc classic 50 trouble

hi, the fuel pump diaphrams on your carbs are probably the culprit they get saggy over time and simply dont pump enough fuel .jim b

 

[microvibe]

Re: 80's merc classic 50 trouble

there is one thing i didnt mention, the top carb is the one wet around the fuel pump gasket but when i keep priming the bulb i will get a stream of gas squirt out of bottom carb but not the top.

also anyone know for sure the model year of this motor i was told it was a 1988 but i think its a 1985 serial number a132588 merc classic 50

 

[microvibe]

Re: 80's merc classic 50 trouble

Ok i have some more info

Resistance Check:

Blue/Blue-white : 12000
Red/Red-White: 150
Brown/White-Black: 780
Purple/White: 780

Coils are all less then 1 ohm on primary side and all at 900 at spark plug wire side.

Serial number a132588 i Believe a 85' merc classic 50, Boat is a 85' alumacraft classic deluxe 16'. Prop says 11p on it.

What are the blue wires for and does that reading my stator is bad? the switch box was replaced last fall.

I ordered new carb kits anyways.

 

[fishingdan]

Re: 80's merc classic 50 trouble

You should not normally see any fuel from the carb (or fuel pump on the carb) at any time. Carb kits are at least part of the answer. All of the fuel system rubber stuff/gasket seem to go at about the same time. Take a careful look at all of the fuel lines (on board the engine and from engine to fuel tank), the bulb, and the fuel line fitting to the engine. With slight pressure on the bulb, you should not fuel from anywhere.

Looks like a 1985 model. I had one till recently. It is a great engine and easy to service. Remove from cowling support to get easy access to the carbs.

If you were dropping a cylinder, the rpms would drop into the 2000s. Sounds like the carb is the initial culprit.

 

[microvibe]

Re: 80's merc classic 50 trouble

well i pulled the carbs off and took them apart.
the fuel pump diaphram looks sagged out moves both way easy with no tension to bring it back to flat. float bowl is sparkling clean and float moves freely. The carb actually looks spotless but fuel pump had gas in every section and gaskets seemed saturated with fuel. Waiting on the rebuild kits to finish up the job then i will try it out before stator replacment. Also after using the boat this weekend mostly trolling and afew atempts at WOT the plugs are black and wet(oil fouled?)

Anyone know is the blue and blue/white wires from stator the high side? and 12000ohm's seems abit high to me, might be why the switchbox had to be replaced last year.

 

[microvibe]

Re: 80's merc classic 50 trouble

Well still waiting on carb kits so i decided to compresion test the engine i am not sure my tester is all that acurate but i got 105 on all 4 cyl give or take a psi. Since they are all the same i am not to worried.

Anyways anyone have an idea why my stator tests showed 12k ohm's on the blue/blue-white wires from what i have read i think that is the low side but my engine starts and idles smooth its the wot where i have the problems.

While i wait on the carbs i might just pull the flywheel off for a visual inspection of the stator and trigger.

 

[microvibe]

Re: 80's merc classic 50 trouble

i pulled flywheel off to visually inspect stator and trigger both look like new but the number on the stator is 398-832075A21 and according to mercury parts express my engine suposed to have 398-832075A20. I looked at the wires coming out of the stator and it has 2 blues 2 reds 2 yellows and then there is a green one cut off at the stator.

Can you use this stator on my motor or is that why the blue/blue-white wires ohm out at 12000ohms? Since my plugs are all wet oil fouled maybe i have weak spark.

any ideas?

 

[microvibe]

Re: 80's merc classic 50 trouble

Would you guys sugest swaping out the stator since the readings are at 12000ohms?

also the trigger merc parts express lists is 964452a4 the one on my motor is 96451, why is every number different on this thing lol.

 

[microvibe]

Re: 80's merc classic 50 trouble

i know i keep asking questions and here is a new one (i think after this repair i am gonna get a manual lol) Just wondering if anyone knows the float hieght its a wma 3 carb the old float is 11/32 on one carb and 10/32 on the other. I took the measurements while carb upside down from where the float cover gasket goes till the top (or bottom ) of float. Next week i should get chance to test it out with new gaskets in carb and new plugs see how it does then the 12000 ohms on the stator still bug me.