50hp power problem

[Michael Sheridan]

I have a late 80's 50hp ,that started fine on the weekend and ran good, i backed it away from he boat ramp turned around and headed forard it took off great just about on the plane then it died back to just above idle, every now and then it would rev just a little and die down again. i continued up river to see if it would come good but it didnt, i stopped and fished for a while thinking it was ok as it had been starting fine, after about half an hour i thought time to move but it would start but not run. any ideas? i am going to clean the carbs on the weekend but wondering if it could be something different.

 

[Maxz695]

Re: 50hp power problem

May be nothing but try disconnecting the mercury tilt kill switch BLK YELLOW ON the switbox.

 

[oldman570]

Re: 50hp power problem

A good cleaniong or rebuild of the carbs should do the trick. You might want to spin the motor over while the carbs are off and check to be sure that the fuel pump is pumping fuel good and steady, as it can be in need of a rebuild also.JMO
Oldman570

 

[Michael Sheridan]

Re: 50hp power problem

Thanks for the help i will try that see if it helps

 

[Michael Sheridan]

Re: 50hp power problem

Ok so I cleaned the carbs over the weekend and tried it out in the river, it took off like a dream was running great got on the plane and stayed there, But as I have to do in Australia I slowed down to pass another boat after that it was only going as it did last weekend. It is starting and running know but as soon as I put it in gear it stalls out. It runs at high idle out of gear but as soon as I put it in gear it dies. The fuel pump is pumping good. Any ideas??:facepalm:

 

[ajgraz]

Re: 50hp power problem

Maybe whatever it was that was blocking up your carbs (dirt, grit, water, bits of disintegrating rubber line?) is still in your fuel or fuel lines. Did you get fresh fuel? How old are your lines, primer bulb, etc.? What kind of fuel filltration do you have?

 

[Michael Sheridan]

Re: 50hp power problem

The fuel is only two weeks old and in a new tank with a new bulb and fuel line going to the motor I will change the lines to the fuel pump and the carbs. But the motor was running fine until it was put into gear I'm thinking timing may be an issue has anyone got any info on what the timing should be when it is in gear

 

[oldman570]

Re: 50hp power problem

We will need the year of the motor to give more as to the timming. Sounds as tho the idle jets are set wrong. Start out with all the idle jets backed out 1 1/2 turns from lightly seated while in the water and in FWD gear and adjust them 1/8 turn in till it stumbles then back them out till it stumbles. Half way between these settings should get you to where you can open it to WOT and you can tweek the setting the with of the screwdriver till it is to your liking. I will need the SR# and year of the motor inorder to give the correct timming otherwise. If the motor ran fine after cleaning the carbs for a while, I doubt the timming is your trouble.
Oldman570

 

[Michael Sheridan]

Re: 50hp power problem

i will try that, it is a 1988 S/N is 9526600, it only ran fine for about 150metres until i had to slow for the other boat, also it doesnt run when in gear, or do i set the 1 1/2 turn before i put it in the water?

 

[oldman570]

Re: 50hp power problem

The setting at 1 1/2 turns out can be done before running the motor. Useing a trashcan or a 55Gal. barrel filled with water can be used for idel setting at home without having to go out on the water. Be sure that the water in the barrel is above the cavition plate as it would be when on the water. Usally 3 or 4'" is good. The final adjustment will need to be done on the water to get the carbs set so there is enought gas mix to let the motor gain RPM and not starve for fuel. All the fuel lines from the tank should be of the same size and have metal hose clamps on the connections. A clear peice of hose can be used from the fuel pump to the carbs for testing of air leaks, by watching for air bubbles, and be replaced with regular line when done. Using a clamp below the primer bulb to hold it in a vertical position will keep the check ball in the bulb in position and not allow it to cause a backflow also. Those carbs have to go back on the motor from where they came off from and you need to mark them as to thier position before taking them off the motor. Using a clear fuel filter in the fuel line will keep any dirt, from the fuel and tank from getting into the carbs and can be replaced as needed. Cleaning the air vent on the front of the carb should be done also. The timming set should be 23 degres BTDC at WOT and should be checked on the water with help from a trusted friend or in a test tank. JMO
Oldman570

 

[Maxz695]

Re: 50hp power problem

The way I see WOT timing done over at the shop down the road they trailer the boat into the water an set the WOT timing on the trailer. Just a suggestion

 

[oldman570]

Re: 50hp power problem

Lots of shops will set the WOT timming this way. It is not a real good way to do it because the motor pushing the truck, trailor back up the ramp is not the same as on the water where you only push the boat and the weight in the boat. Alot of diffrence of reistance there that could cause the motor to have the WOT timming set to far BTDC. Test tanks or on the water are best and the reading will never change because of the less resitance. JMO
Oldman570

 

[Michael Sheridan]

Re: 50hp power problem

Ok so I cleaned the carbs out again,found a little bit of dirt in the bottom one. Replaced all the fuel lines and the fuel filter and has seemed to fixed the problem, but I did notice that it is a bit thirsty for fuel is that common? so thanks everyone for the help

 

[quicktach]

Re: 50hp power problem

I have a late 80's 50hp ,that started fine on the weekend and ran good, i backed it away from he boat ramp turned around and headed forard it took off great just about on the plane then it died back to just above idle, every now and then it would rev just a little and die down again. i continued up river to see if it would come good but it didnt, i stopped and fished for a while thinking it was ok as it had been starting fine, after about half an hour i thought time to move but it would start but not run. any ideas? i am going to clean the carbs on the weekend but wondering if it could be something different.

Sounds like your timing may not be advancing properly and staying in position. And your trigger coil could be sticking or with limited movement under the flywheel. Could be a broken or loose plastic part or jammed up linkage too.

Once you're satisfied you've done everything on the fuel side of the problem, go to the electronics. And check everything. If all else works out ok, you could have an erratic CDI problem. Check all your grounds to make sure they are clean and tight.

 

[ajgraz]

Re: 50hp power problem

Ok so I cleaned the carbs out again,found a little bit of dirt in the bottom one. Replaced all the fuel lines and the fuel filter and has seemed to fixed the problem, but I did notice that it is a bit thirsty for fuel is that common? so thanks everyone for the help

These old non-looper Mercs are thirsty alright. Do you spend a lot of time at idle? Maybe your carb idle screws are now too rich, as 1-1/2 turns is just a beginning setting; did you go through and turn them in an 1/8 to a 1/4 turn at a time while testing holeshot?

 

[oldman570]

Re: 50hp power problem

As a rule of thumb a 50 hp will go thru 5 gal. of fuel per hour when run at WOT or close to there,and less at idle. The dirt in the carb was probly the trouble as thought. If using gas with ethenoal you should replace all the fuel lines with new ethenoal reistance ones, and check the Puregas.org site for stations that sells non ethenoal gas in your area. Most motor manufactures have run test running ethenoal fuel and do not recommend its use. The addition of a clear fuel filter between the tank and primer bulb will help keep things running better. ethenoal tends to eat up and corroed any rubber or metal parts of the carbs. JMO
Oldman570

 

[Michael Sheridan]

Re: 50hp power problem

didnt spend much time at ilde most of the running was at WOT, just slowing for other boats and to make sure it would run at idle as well

 

[Michael Sheridan]

Re: 50hp power problem

does any one know how fast this should go with a 4.25m aluminuim hull, i think it is a deep vee hull

 

[oldman570]

Re: 50hp power problem

There are several things that determin just how fast the boat will run. Weight, prop size, RPM of the motor are just a few. The weight of the boat and the RPM of the motor at WOT should deturmin the sizeand pitch of the prop that will be best for the best performance of the boat. A check on the the prop form here on Iboats or one of the prop Manufacture websites will help one understand what all is involved. A prop that lets the motor run in the 5000 to 6000 RPM ramge at WOT and not let the motor overrev nor not reach those RPM's would be my choice. A prop with a 11 to 13 pitch will probbly work best. If the speed of the boat is a big factor and one wants more then a larger motor should be the answer. JMO
Oldman570