88 Mercury 100 hp fuel/carb questions.

[holorinhal]

I have a 1988 oil injected 100 hp merc. It had been sitting for about 15-18 years, since my dad took the motor off the boat, because he thought it had a oil problem, due to a constant beeping oiling alarm.
I have since figured out that it was a problem in the oil tank, with the float.
I have got the motor to fire up and run, however, it will run rough and wont run for long, on its own or sit and idle on its own, with out aplying throtle.
While running and applying throtle, i noticed that fuel sprays into the carbs, only on the midle two carbs( #2 & #3).
I have a new pump bulb and fuel suply line, however, I am drawing fuel from a regular gas can. Is this ok, or are the outboard fuel tanks preasureized?
I have checked the compresion and all cylinders read 120 psi, except #3 which reads 115psi.
Are all four carbs supose to spray fuel on acceleration. Is it possible that #1 and #4 are cloged?

 

[oldman570]

Re: 88 Mercury 100 hp fuel/carb questions.

Yes it dose sound like the carbs need to be cleaned/ rebuilt. Without the needed fuel being supplied to the motor by the two carbs in question, you are lucky that it even stayed running at all. It would be in your best interest to do a by step engine tune up and start with decarb of the cylinders. then cleaning the carbs, and testing the fuel pump. And yes all of the carbs should squirt fuel when accelerating.
The service manual for the motor should be the first item you need to buy if you do not have one already. I would use a fuel mix of 50/1 till you are sure that the oil pump is working as intended, just incase it is not. I have bypassed my oil injection and run a fuel mix all the time in my motors. This way I am sure that the motor is always getting the oil it needs.
Drawing fuel from a regular gas can can be done, but it would be best to use a regular marine fuel tank/can. The compression readings are good for a motor that has not run as stated, and the decarb and running might bring it up to the rest of the readings.
Here is a link to and online manual that can help with the troubles,
Boatinfo - Mercury Service Manual for 70-75-80-90-100-115 hp
Let us know how things are going or if there are other questions you might have. JMO
Oldman570

 

[BatDaddy1887]

Re: 88 Mercury 100 hp fuel/carb questions.

....don't forget to install new plugs as well....maybe two sets as you will need to decarb like oldman570 says....

 

[holorinhal]

Re: 88 Mercury 100 hp fuel/carb questions.

Yes it dose sound like the carbs need to be cleaned/ rebuilt. Without the needed fuel being supplied to the motor by the two carbs in question, you are lucky that it even stayed running at all. It would be in your best interest to do a by step engine tune up and start with decarb of the cylinders. then cleaning the carbs, and testing the fuel pump. And yes all of the carbs should squirt fuel when accelerating.
The service manual for the motor should be the first item you need to buy if you do not have one already. I would use a fuel mix of 50/1 till you are sure that the oil pump is working as intended, just incase it is not. I have bypassed my oil injection and run a fuel mix all the time in my motors. This way I am sure that the motor is always getting the oil it needs.
Drawing fuel from a regular gas can can be done, but it would be best to use a regular marine fuel tank/can. The compression readings are good for a motor that has not run as stated, and the decarb and running might bring it up to the rest of the readings.
Here is a link to and online manual that can help with the troubles,
Boatinfo - Mercury Service Manual for 70-75-80-90-100-115 hp
Let us know how things are going or if there are other questions you might have. JMO
Oldman570

Yes I am using a 50/1 fuel mixture from the gas can. I did download a manual a while back, this one, http://1manual.com/Mercury%20manuals/Service%20Manual%20PDFs/TwoStroke/13645_2/cover.pdf which apears to be the same. Thank you for the link.
I had a constant beeping alarm, so I replaced the reed sensor, but did not stop the alarm. I drained then took the oil tank off. I found that the float was stuck and or not moving up and down, it was just staying down, trigering the alarm. I could reach in, with the sensor hooked up and key on, and pull the float up and the alarm would stop. I turn the key on and get one quick peep to sinify circuit operational. push float back down and constant alarm. for some reason the float would not float.
Oldman570, what is meant by decarb the cylinders? and what is the process, or is it in the manual? does it have to do with removing carbon? Thank you,,,,,

 

[oldman570]

Re: 88 Mercury 100 hp fuel/carb questions.

The decarb of the motor is when you place a cleaner in the fuel or in the spark plug holes to remove the carbon build up from the pistons, rings, and the rest of the motor. There is a post in the sticky's here at the top of the forum or a search will get many ways to do the decarb. I use Sea Foam to do the decarb on my motors. The easiest way is to mix a 16 oz.. can of sea foam with 1 gal. of gas & 3 oz. of oil and run the motor at idle to no more than fast idle for 15 min. then leave the motor set for 1 hr. then repeat the step 2 more times. The motor will smoke like crazy as the carbon is being burnt off and make sure you do it when the neighbors are not around to call the fire dept. over it. After that you should run Sea Foam in the gas as directed on the can about every 40 hrs. of run time to help keep the motor in good shape. Here is the link to the sticky I mentioned and a thanks to the members that wrote it and made it a sticky.
http://forums.iboats.com/engine-frequently-asked-questions-faq/decarbing-faq-158076.html
There are other decarb products that can be used also. JMO
Oldman570