Engine won't run under 1500 rpm

[Skip31]

I got a problem with our port 5.0 mercruiser 1995 model 450b11ohu
when first start up it will run at lower rpm but after warm up it won't.. runs find above 2000rpm..the starbore engine runs fine so its not fuel problem.
change the fuel /water filter on the port engine,new plugs and cleanned the fire arrester, Also took the carb apart and it looks clean,but I took out the jets just to be sure...but they were clear..Could not get to the low speed jets as that might be the problem, But with out knowing what carb it is I am not sure ..
The engine number says its a 4 bbl but they are not ! So Im not sure if the carb is a rodchester or a merc 2 bbl carb. so I can get a rebuild kit..
Mercruiser model 450b11ohu of590832 of614063 off of the warraanty reg card..
Got any ideals ?
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[GuyG]

" Im not sure if the carb is a rodchester or a merc 2 bbl carb."

Rochester carb has two idle/mixture screws while Mercarbs have one. Before rebuilding the carb, remove the carb top, siphon out the gas w/a turkey baster then fill the bowl w/SeaFoam and close it up. Run the engine 2 mins. and turn it off. Let it sit o'night and run it the next day. If there is still a problem then rebuild.

[Skip31]

" Im not sure if the carb is a rodchester or a merc 2 bbl carb."

Rochester carb has two idle/mixture screws while Mercarbs have one. Before rebuilding the carb, remove the carb top, siphon out the gas w/a turkey baster then fill the bowl w/SeaFoam and close it up. Run the engine 2 mins. and turn it off. Let it sit o'night and run it the next day. If there is still a problem then rebuild.

It has one idle adj at the bottom of carb. So I quess its a merc.
Looking at a parts diagram its a merc 2 bbl...
Thanks will keep you posted.
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