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Mercarb Marine Carburetor
Float Level Setting - Our carburetor kit includes 2 different types of needle & seats. One is spring loaded and the other is the solid type. The spring loaded type of needle & seat is the preferred type, especially if you are having a flooding problem at idle. The trade off is that you may have a lean out (fuel starving) on sharp turns. Make your decision based on how you use your boat.
2 piece solid needle & seat
10 mm
1 3/32" 27 mm
spring loaded needle & seat
9/16" 14 mm
1 3/32" 27 mm
How to Identify your Mercarb
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 the engine.

There could be a vacuum leak. Since the carburetor was recently removed, I would check the flange gasket to make sure it isfitting as it should. A leak here will, a lot of times result in a high pitch squeal. Any place where vacuum can escape is suspect, but if it idled ok before tackling the carburetor, then you can probably rule that out. Check the gasket between the float bowl and the throttle body. If the kit had more than one choice for a gasket here, then make sure you used the correct gasket. Improperly installed throttle valves can also cause an air leak. Assuming you took the throttle plates off for cleaning, make sure they are closing all of the way when the throttle is closed. You may have to turn the idle screw out to check this. Remember, the idle screw is used to open the throttle plates a little bit.

Check Ball Question
The exploded view of the instructions sheet that came with my MerCarb carburetor kit includes a check ball and screen at the bottomof the accelerator pump well. Mine seems to be missing. Not all Mercarbs have the check ball and screen. This type of Mercarb will not have a hole in the bottom of the well to support a check ball,or the screen. What is the check ball size for the Mercarb?
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 Linkage
Mercarb Choke Thermostat
Mercarb Thermostat
Accelerator Pump Adjustment
MercarbSome Mercarb carburetors will have an accelerator pump lever with 3 holes. This will allow you to change the amount of fuel delivered by the accelerator pump. Start with the center hole which will give you the full accelerator pump stroke. (b) .5 cc less fuel per stroke, (c) 1.0 cc less fuel per stroke.
Mercarb Choke Housing Replacement Video
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