|Mercarb Marine Carburetor
We carry two different kits for the Mercarb carburetor. You will have to pop the top to inspect the accelerator pump to determine which pump you have. You want to know which one you have before ordering your carburetor kit unless you have the carburetor number. These carburetors are switched back and forth by the boat repair people, so don’t assume you have the original carburetor.
One has a straight shaft accelerator pump.
The other Mercarb kit has a 90 bend at the top of the accelerator pump.
|How to Identify your Mercarb||
Soak your carburetor parts in a
gallon of carburetor cleaner (brand doesn’t matter), any parts store
brand. Keep in mind that none of the cleaners will do a great job, but
the existing cleaners is all we have.Soak overnight.Wash with hot water
– remove all chemical.
Blow out all passages with compressed air.
Run thin wire through all passages. Ethanol will leave residue behind
that cleaners cannot remove.
Using soda blasting to get corrosion out of the bottom of the
carburetor is ok, but be sure to get it all out when done, otherwise
you will have clogged passage ways.
Keep WD 40 and like products away from your carburetor. It all reacts
|Watch a video about rebuilding the Mercarb.Part 1 – Teardown
Mercarb Rebuild – Part 2
I just recently rebuilt my carb
using your rebuild kit. I have a Mercarb 2bbl that fits a Mercruiser
3.0L. The carb is a 3310-80750. In your documentation, you state to set
the idle jet at 2 turns turns out. The merc manual says to use 1 1/4
turns. I initially set it up using the 2 turns and the engine fired
right up without any issues. It ran great on a test run but I can’t get
it to idle at the recommended 650-700 rpm. The lowest I could get was
900. I adjusted that jet to the1 1/4 turns but still couldn’t get a low
idle. I triple checked the float levels when reassembling so I am sure
that it is fine. All parts went back together and the whole thing was
cleaned and blown out with air so I don’t think the problem is
internal. I still have to check linkage and choke plate, etc. I hope
that is where the problem lies. What do you recommend for needle jet
setting? 1 1/4 or 2?
The initial setting for the
idle mixture screw is simply the initial
setting. Once the engine is started and warmed up you will need to
adjust the mixture screw further. There are a couple of ways to do it.
The most accurate way is to hook up a vacuum meter at the carburetor
and adjust the idle mixture screw until you get a smooth vacuum. Now
this can only be done when the engine is at idle rpm, which leads me to
the 2nd issue. There are more than one possibility for the engine not
idling down to specifications. In simple terms, there is too much air
getting to theengine.
Check Ball Question
Both balls are 5/32″. When one
is aluminum, put it in the bottom of the accelerator pump. The other
ball goes into the main discharge hole.
|Mercarb Linkage Setup|
|Mercarb Choke ThermostatMercarb Exploded
Installed item K529 for Mercarb (carb #807504N) this weekend and carb
number and parts fit lead me to believe it was correct one. Everything
cleaned up well but boat won’t start unless held wot (like it’s
flooded). Once started it runs clean at 2000rpm while warming up but
won’t idle smoothly. Choke is open and idle mixture screw was started
at 2 turns out and adjusted both ways from there without making much
difference. The screw was slightly different length than old one but
seemed to bottom out lightly without issue.
With air cleaner off it seemed to dump fuel into engine after shutdown.
Needle and seat were adjusted and I used the spring loaded one.
Installed brass colored spring and check ball under venturi cluster.
Any idea what I am missing to get this thing idling correctly?
I suspect you are getting too much fuel. Here are the items to check:
Followed all instructions
Assuming the electrical and engine are in top condition…..
1st of all, if he carburetor has not been cleaned and rebuilt, I would
Using thin wire, make sure all of the passages on the venturi cluster
Make sure the passages under the main jets are not clogged.
Check the fuel pump pressure. It is possible it is crapping out at high
Welcome to Mike’s blog. I hope you find my articles helpful as well as informative. I welcome comments on any of my articles. You might also want to sign up for my email notification so that you are notified any … Continue reading
We have 4 different types of chokes, Intregal, Divorced, Electric & Electric Conversion.
The integral choke is mounted on the carburetor, either near the top, or near the bottom. The illustration shows the choke mounted on the top of the carburetor. The thermostat is heated by a heat tube that runs down to the exhaust manifold. The heat tubes heats up the thermostat and moves the choke valve to the open position. A vacuum passage in the carburetor feeds up to the choke housing and helps pull in the heat from the heat tube. Some of these chokes will also have a hot water jacket running through, or on the thermostat to facilitate heating.
The divorced choke typs has the thermostat mounted in the intake manifold instead of on the carburetor. In this illustration, the arrow points to the thermostat which is covered by a metal shield. A rod connects the thermostat to the choke lever, which controls the choke valve to be opened, or closed. As the intake manifold heats up, the thermostat mounted, expands, opening the choke valve.
This is a typical electric choke mounted on the carburetor, which is integral. In this case there is one wire on the choke thermostat. This is the 12v source, which all electric chokes use. The thermostat is grounded via the carburetor itself. Some electric chokes will have a 2nd wire (ground wire), which is connected back to the carburetor. When the key is on the thermostat is heated up, opening the choke valve.
|Electric Choke Conversion
This is a typical electric choke conversion kit. This is used to convert an integral, or a divorced choke to an electric choke. These choke kits come with a temperature sensor that bolts on to the intake manifold, which provides more accurate choke control than with an electric choke without the gauge. The electric choke conversion kit is not used for a manual choke conversion. The choke housing must be in place in order for it to work.