Mercury brown band 75 hp 4 cyl.

[markodecember]

Hi folks,

I went to see a boat the other day that had the above engine fitted to the boat.
Compressions were satificatory (135psi) but the problem is that it would only start and run on 1/2 to 3/4 throttle.:redface:
I rekon it has got to be a problem with the carbs being blocked and just needing a good clean.
What are all you thoughts on the matter?! Am I right to presume carb problem?!
It did look as it had been sat around for ages- only a dribble coming from tell tale and clearly not been moved for at least a year or two.
All replies very much apperciated.
Many thanks,
Mark.

 

[hamit59]

Re: Mercury brown band 75 hp 4 cyl.

Hi,


Do the spark test. If you find out if you have good spark. (jumping 3/8- 7/16 gap) You could be dragging a cylinder due to poor spark..
You should go to the fuel system starting at the tank make sure everything is clean and there is no restrictions or air leaks in the fuel lines or primer bulb and the disconnect.
Then you need to check your fuel pump.or rebuild it parts are cheep.
Last but not least the carb cleaning and rebuild.
You really don't know how long the motor has sat unused. Hot weather will
evaporate the gas left in the carbs bowls and leave a goo at the bottom of the carb.
I always run my motor until it stops to help( disconnect the fuel line) with that high speed jets are at the bottom of the carb. Some on here will say you don't need fuel treatment,
I use it on every tank full, it works for me.

After you get the motor running well.

Pull the prop and grease the prop shaft
this will let you see if you have any fishing line on your prop shaft that will cut your prop shaft seal.
Drop you lower lube look for milky oil and water and any metal chunks.
Any of these you would need to look deeper into the lowerunit
Replace the water pump as a whole kit
I hope this helps.
I hope you reply back to let us know what you find.

 

[Chris1956]

Re: Mercury brown band 75 hp 4 cyl.

Mark, As was said, put a timing light on each cylinder and crank the motor to see if you have spark to all cylinders. If so, remove the 2-4 plugs, tape them together and to the block, such that they are all grounded. Now with a timing light on #1 plug wire, advance the throttle with the cold start lever until the carbs just start to open. Crank the motor and check the idle timing against spec. Now advance the throttle until full throttle, and using a jumper, engerize the starter solenoid to crank the motor. Check the max spark against spec. If these are correct, I would thnik the carbs are the next to require attention.

 

[rvbilly]

Re: Mercury brown band 75 hp 4 cyl.

did you get the serial # off the engine ? Usually the brown band engines are a 1980`s erra engine ...

 

[markodecember]

Re: Mercury brown band 75 hp 4 cyl.

Hello thanks to all that have replied.

Firstly unfortunatly I do not have a serial number for engine but I am 95% sure in was built in the mid 1980's probably 85-86.
If you read the original question I simply went to inspect the boat and engine and currently do not own the outboard motor.

As to regards for the timing, I am not a marine engineer so I don't have access to a timing gun etc
So the only real thing I can do is clean and inspect the carbs and generaly service the engine. All I wanted to ask is what is the likely hood that the a blocked carb is the intial source of the problem

I thought that this was the mostly likely contender as I know it has been sat around for a few years looking at the general contiditon of the boat. But again I extent my gratitude to thoose that have helped me and given advice as to where the problem of the engine only running on 1/2 to 3/4 throttle.

Another quick Q : (sorry) The trim and tilt was not raising or lowering the engine at all
I could here the solenoid clicking when the switch on the controls was used. Is this a dodgy solenoid or are the rams shot ?!
Any info would be great.

THANKS TO ALL
Best regards,
Mark.

 

[Chris1956]

Re: Mercury brown band 75 hp 4 cyl.

Mark, If the motor has good compression, everything else can be fixed rather easily. It could just be a dirty carb or two. of course, the ignition may be malfunctioning, or the motor out of time.

The cost of these repairs will be small to moderate if you can do the diagnosis and repair. If a shop does the work, the repair cost may be a lot higher than you care to pay. The shop might charge $150-200 to clean and rebuild the two carbs. The shop might charge the same to set the timing. if the ignition is in need of repair that would be additional. I would also check with a shop to see if they will even work on it. Some will, some won't.