Mercruiser 3.0LX Idling at 1000rpm

After being on here for 3 year, I finally got a problem that I cannot figure out. Here is my boat information:

Mercruiser 3.0LX (1991) with Alpha I Gen II Outdrive
Rochester GC 2 Barrel Carburetor

I just rebuilt my carburetor and for some reason I cannot get it to idle below 1000rpm. Here are ALL the things that I have done:

1. Rebuilt my Carburetor (I double and triple checked everything during this rebuild, everything clean, new float in place, and base gasket)
2. Fresh tank of fuel (non-ethanol)
3. New Fuel/Water Separator
4. New Spark Plugs, Wires, Distributor Cap, and Rotor
5. New filter for fuel pump.
6. New fuel lines
7. Oil Change

When I placed the carburetor on and started her up, she was idling at 2000rpm. I backed out the Idle Speed Screw from the carburetor to the point that is now not even contacting the idle cam and she is still idling at about 950-1000rpm. I also have the accelerator cable disconnected from the carb. I have even tried leaving some pressure on the cable so it is pushing back on the accelerator. Note that this is on the trailer with muffs in place. I realize that final adjustments should and will be made on the water with it in forward gear. I figured though I should be at about 800rpm on trailer and will drop about 150rpm when I hit the water.

I have read a lot of "idles rough under 1000rpm" but I cannot even get her below 1000rpm to see if she will run rough or not.

Thank you to anyone that can help me with this problem. I am sure it is just some "small" thing that I am missing.

Re: Mercruiser 3.0LX Idling at 1000rpm

Disconnect the throttle cable from the carb and see if it idles down.

You may need to adjust the cable to get just a light preload to the idle position.

Re: Mercruiser 3.0LX Idling at 1000rpm

Already done that Mr. Don S.

Right now the cable is off from the carburetor. Also before removing the cable I had some preload on it to push back the accelerator on the carb (Preload)

Re: Mercruiser 3.0LX Idling at 1000rpm

Spray some carb cleaner or WD40 around the base of the carb and see if the idle changes. You may have a vacuum leak

Re: Mercruiser 3.0LX Idling at 1000rpm

.....I do need to double check that. If there is a leak, will my idle raise or lower with spraying WD-40? Also, I set my float level to 16mm and my drop to 1 29/32. Again, note this is a Rochester CG 2 Barrel Carb on a Mercruiser 3.0lx. Do those measurements sound right to you Mr. Don S?

Thanks....I really do apprecitate everything. I am gonig to feel like an idiot if there is a leak at the base gasket

Re: Mercruiser 3.0LX Idling at 1000rpm

.....I do need to double check that. If there is a leak, will my idle raise or lower with spraying WD-40?

Click to expand...

Ayuh,.... Welcome Aboard,... Yer lookin' for a Change in the rpms, more so than up or down...

Re: Mercruiser 3.0LX Idling at 1000rpm

Mr. Bond-o, do you know if I have the correct float level and drop that I have posted before? Mr. Don S never responded (I am sure he is a busy guy).

I just want to be sure that I am doing EVERYTHING correct. I have learned with boats.......Maintenance Now........or Pay Later

Re: Mercruiser 3.0LX Idling at 1000rpm

cptbraine31 said:

Mr. Bond-o, do you know if I have the correct float level and drop that I have posted before? Mr. Don S never responded (I am sure he is a busy guy).

I just want to be sure that I am doing EVERYTHING correct. I have learned with boats.......Maintenance Now........or Pay Later

Click to expand...

Ayuh,.... I ain't had 1 of those carbs apart in Years,.... a Manual oughta tell ya though,...

I don't have a link at my fingertips, but I'm sure somebody'll be along that does....

Re: Mercruiser 3.0LX Idling at 1000rpm

Bond-o said:

Ayuh,.... I ain't had 1 of those carbs apart in Years,.... a Manual oughta tell ya though,...

I don't have a link at my fingertips, but I'm sure somebody'll be along that does....

Click to expand...

Yeah, I have looked all over the place for a manual. I have found some Rochester manuals but NONE of them state anything about the proper float level and drop.

Re: Mercruiser 3.0LX Idling at 1000rpm

Check the papers that came with the rebuild kit. When I did mine the kit had a list of proper measurements and came with a little measuring tool.

Re: Mercruiser 3.0LX Idling at 1000rpm

None of the LX carbs were Rochester, they are all Mercarbs. They look almost identical to a Rochester at first glance, but the Mercarb only has a single idle mixture screw where the Rochester had 2.

What is the serial number of your engine? Is there a carb number as well?

Re: Mercruiser 3.0LX Idling at 1000rpm

Sorry Don S, I am not at home right now and do not have those numbers on me (I think the carb is 7046532). Yes sir, I know the LX did not have the Rochester but the Mercarb, but I promise, mine is a Rochester (2 idle/mixture screws). I think the gentleman that owned this boat before me bought one of those reman carbs online and ordered the wrong one.

Before the rebuild the boat was running fine but it was due for a rebuild.

Re: Mercruiser 3.0LX Idling at 1000rpm

thumpar said:

Check the papers that came with the rebuild kit. When I did mine the kit had a list of proper measurements and came with a little measuring tool.

Click to expand...

Had it all EXCEPT the darn float level and drop.............welcome to my world

Re: Mercruiser 3.0LX Idling at 1000rpm

cptbraine31 said:

Before the rebuild the boat was running fine but it was due for a rebuild.

Click to expand...

Why was it due a rebuild, that is not something that is done like changing the oil or a tuneup.

I'll see what I can find on that carb number.

Re: Mercruiser 3.0LX Idling at 1000rpm

Don S said:

Why was it due a rebuild, that is not something that is done like changing the oil or a tuneup.

I'll see what I can find on that carb number.

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Well sir, at the end of last season seemed like the boat was not idling well. Figured rebuild carb time. Took carb apart……water damage (white hard flaky material in the carb). So I soaked and cleaned the carb until you could perform surgery on it. That is why I installed a water/fuel separator, changed ALL the filters, and replaced ALL of the fuel lines (just to be sure).

I am just a 4th year boater and I really try and keep my maintenance up.

Re: Mercruiser 3.0LX Idling at 1000rpm

Well, that didn't take much. All the float levels for the 2GC are 5/8" Float drop looks like 1 7/16 to 1 7/8' That's easy to check, all the float drop does is keep the float from touching the bottom of the carb and stirring up dirt if there is any in there. Just measure the dept of the bowl and give it an 1/8" clearance.

Re: Mercruiser 3.0LX Idling at 1000rpm

Don S said:

Well, that didn't take much. All the float levels for the 2GC is 5/8" Float drop looks like 1 7/16 to 1 7/8' That's easy to check, all the float drop does is keep the float from touching the bottom of the carb and stirring up dirt if there is any in there. Just measure the dept of the bowl and give it an 1/8" clearance.

Click to expand...

...Thank you so much Mr. Don, I really do appreciate ALL of your help on this matter. I really hated getting on here and asking but I was just out of ideas. I am going to double check the float and also check the base for leaks.

I will let you know the results of the adjustments/checks you advised me on.