90' yamaha 150 stuttering at rpms above 1800

I've got a 1990 yamaha 150 with only 300 hrs on it. It ran great before I replaced it and now I'm putting it back on due to a theft. Anyways it has all new plugs wires coils, newly rebuild carbs from top to bottom, new arm that holds it in sync, now oil pump and water pump. I got it on the the boat with all the new parts and had it running great. We went out fishing and ran like a bat out of hell. The next night we went out and got about half way to my fishing spot ( about a mile ) and the thing bogged down and wouldn't exceed 1800 rpms with out shuttering like its bouncing off a rev limiter. Can anyone help? I've seen posts about it but no one tells what fixed it

Sounds suspiciously like rpm limiter related to an overheat or low oil. It is possible that your warning horn is non functional also so you aren't aware of either. Do you have an arrow on your tach indicating either?

No, there isn't an arrow for the rpm. There is one above the oil level but it has always been like that and it was running great with it like that

I suspect that you do not have a functional warning horn. You can verify that by grounding the pink wire on your heat sensor when the key is on. You should hear the horn. Also check to see if your oil tank under the cowl is filling. If the oil level is down to the lower line you will go in to rpm reduction. If the oil transfer filter on the back of the remote tank is restricted you will fill to slowly to keep up with consumption.

PBRMAN said:

I suspect that you do not have a functional warning horn. You can verify that by grounding the pink wire on your heat sensor when the key is on. You should hear the horn. Also check to see if your oil tank under the cowl is filling. If the oil level is down to the lower line you will go in to rpm reduction. If the oil transfer filter on the back of the remote tank is restricted you will fill to slowly to keep up with consumption.

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Yes that is correct my horn is not working. There is plenty of oil in the tank and it is keeping up with consumption. However my oil low level light is on warning me of such thing but it has always been like this even when it was running great. The problem just happened out of the blue while I was on a plane about an hour On my way! To my destination and just suddenly bogged down and would not exceed the 1800 rpm.