1988 Mercury 100hp Carburetor cleaning Help

[bryman04]

Hi everybody.

I have been attempting to read all of the information that I can regarding the subject of cleaning the carbs on my 100 merc. The boat had been struggling to run for some time and squeezing the fuel primer bulb helped. I don't know when the last time the carbs were cleaned, but following the advice of others who have had similar problems I have bought a gallon of the Berryman Chem Dip to use in cleaning (even though the manuals warn against it).

My questions come to WHAT I need for rebuild/replacement parts. I went to the Marina today and bought 3 gasket kits ($8 each) and 1 rebuild kit with gaskets/screws ($38) for the carbs. Do I need to buy rebuild kits for all of the carbs or can I just replace the gaskets??

Also when it comes to using the Berryman's chem dip stuff, can someone who has used it give me a quick run down of how to go about it? Did you take the entire carb apart or leave some pieces assembled when you dipped it? How long did you dip the parts for?

I am also planning on rebuilding the fuel pump too... Any thoughts?

Any advice would be appreciated!
bryman04

 

[Jlawsen]

Re: 1988 Mercury 100hp Carburetor cleaning Help

Berryman Chem Dip works but it will remove the Alodine that's been keeping them from corroding for all these years. Just use Gunk Carb cleaner. Disassemble them completely and soak them for 24 hours. Rinse them in warm soapy water and then blow them dry with compressed air. Make sure all the passages are clean and clear but do not use anything but compressed air to clean them. No wire brush strands or anything like that. I mean, you can but just be very careful not to hone out the ports or shove something deeper that might have come out by using a little more air pressure from the opposite direction.

Now lets talk about your motor. This motor is what's known as a 2+2. It runs on two cylinders up to about 1700 rpm and then a fuel enrichening accelerator pump pushes fuel into two check valve style injectors on cylinders 3 and 4. This helps with the transition as the carbs for 3 and 4 begin to provide adequate fuel for combustion. Before that the carbs for 3 and 4 provide just enough fuel for lubrication but not combustion.

It sounds complex but it's really a very simple but ingenious way to make a big motor run at trolling speeds without loading up.

So here's the caveat - do not mix up any of the carb parts paying special attention to the jets and their locations.

The one thing that makes these motors stumble and transition badly is the tiny 1/8" filter that's located behind the oil tank. If this gets plugged the checkvalve injectors dry out and stick and it's usually in the closed position. Fortunately, these are easy fixes and once it's taken care of, you'll think you added a super charger to the motor.

As for gaskets, most of the time a basic gasket kit will do the trick but if you need to replace floats or float needles and seats then you need the full kit. Often you have to order the floats and float needles/seats separately and can save some money by just getting them and the basic carb kit.

 

[aussieflash]

Re: 1988 Mercury 100hp Carburetor cleaning Help

Pretty sure your floats will be the plastic ones(not foam) so they rarely fail.I would go with the gasket kits and buy needle seat assembly seperate.
Cleaned mine with carb cleaner(soak only 1 hour),then rinse with water,then final rinse with solvent(mineral terps),then blowout with compressed air.
Fuel pump should also be rebuilt.

 

[bryman04]

Re: 1988 Mercury 100hp Carburetor cleaning Help

The one thing that makes these motors stumble and transition badly is the tiny 1/8" filter that's located behind the oil tank. If this gets plugged the checkvalve injectors dry out and stick and it's usually in the closed position. Fortunately, these are easy fixes and once it's taken care of, you'll think you added a super charger to the motor.

Jlawsen can you give me more info on this? Is that filter part of the fuel system or the oil system? I will look today, but so far I haven't been able to figure out what filter you are describing. Is the fix just installing a new filter?

 

[CharlieB]

Re: 1988 Mercury 100hp Carburetor cleaning Help

clean the carbs, rebuild the fuel pump, replace any/all fuel hoses and primer bulb.

Then the tricky part, adjusting the carbs, linkage, and timing.

Get a FACTORY service manual, it spells everything out in a neat orderly manner.

Check these links to see if your model and serial # are available for download

http://1manual.com/Mercury manuals...ual_Index.html

http://forums.iboats.com/showthread....11#post2072211

 

[bryman04]

Re: 1988 Mercury 100hp Carburetor cleaning Help

So here's an update.

Yesterday I spent all day cleaning the carburetors (Berryman Carb Dip for 1 hour), replaced the carb gaskets, rebuilt the fuel pump, replaced the fuel filters (both of them- Thanks Jlawsen!) primer bulb and main fuel hose and put new spark plugs in the boat (all plugs were firing perfectly). My problem is still happening though.

I went to start the engine in the driveway with the muffs on it and it would maybe run for 3 seconds, then sputters and dies. For me it seems pointless to put the boat in the water if I can't get the engine to at least RUN (rough or not) so for now I will be doing things from the driveway.

I have not yet tried to hook up an alternate tank to the engine to see if that works, but that will be one of my next steps. *It almost seems like the engine is burning what fuel is primed into it, then there is no vacuum to keep it running/flowing.*
When I did have it running, I was tinkering around and began pressing in the "enrichner" button and this helped dramatically to keep the engine running (that's the "choke" right?).

For a little more background, and this may be a huge factor, my father-in-law (who owns the boat) was replacing a part of the boat's floor and in doing so cut into the top of the gas tank (thank God it was plastic ). He sealed the cut with a plastic epoxy and it seems to have repaired it. I thought that might affect the vacuum/fuel flow into the tank but he said that there is no vacuum in the fuel tank...


Any thoughts? All feedback is GREATLY appreciated and will be put to the test, so THANKS! in advance.

 

[bryman04]

Re: 1988 Mercury 100hp Carburetor cleaning Help

In addition to my previous post:

When cleaning the carbs I did not clean the "inlet needle" as I did not want to put it in the carb dip and have the little rubber end points melt off... They all seemed to move and slide fine when re-attached to the floats, which also looked good, however now I am wondering if this is my problem.

 

[aussieflash]

Re: 1988 Mercury 100hp Carburetor cleaning Help

Did you adjust float height to correct spec?Worn needles/seat are hard to pick,better to replace them,probably due anyway.Only $10 each.
If it has a anti siphon valve,remove it and throw away.
Have you checked your compression lately?What #s are you getting?

 

[CharlieB]

Re: 1988 Mercury 100hp Carburetor cleaning Help

Starting a cold motor you must push the choke/enrichener releasing as the motor fires. During the first minute of running it is normal for the 'cold' motor to falter and die unless you are quick to 'touch' the choke/enrichener. This can happen a few times until the motor warms enough that it no longer needs that additional fuel to run.

Test fuel supply to the carbs, disconnect the fuel hose from the fuel pump and temporarily install a clear hose, start the motor and watch for any air bubbles passing thru the hose. This will quickly show if air is sucking into the system somewhere between the fuel tank and pump. Be SURE to remove the clear hose when finished as it is NOT rated for fuel.

Personally, I would be very wary of a plastic fuel tank that has been repaired. And I have a long history of using epoxy adhesives.

Even if the plastic was properly cleaned, the surface scuffed, the mixture perfect, the possible consequences of a fuel leak on a BOAT are not worth the risk. We are talking LIVES, your's, those on the boat or dock nearby, any possible FUTURE owner.

A metal tank could have been welded, a safe permanent repair.

Risking lives on any adhesive is simply not done. Except to hold the heat shielding tiles on the space shuttle.

 

[bryman04]

Re: 1988 Mercury 100hp Carburetor cleaning Help

After cleaning the carbs and doing more diagnostic work, we rebuilt the fuel pump again with a different kit. The old kit had a large "plunger" and the new kit had a smaller one. With the new fuel pump kit the motor stayed running We got it out on the lake today and it does run well, however there is a very noticeable tick/knock while the engine is running. Any ideas?