I have a 1988 Mercury 35HP motor that I am only getting 3100 rpm full throttle while under load on the water. I can put muffs on the motor and rev to 5000 rpm with the fast idle lever and with the throttle. This is my first boat and would appreciate any help I can get.

Here is a little info on the motor. My father-in-law bought this boat new in 1988 and only had it on the water maybe a dozen time and hadn't had it on the water since 2001, but has put muffs on it every now and then to run it at the house. I recently got the boat from him and after some fresh fuel it fired right up. I took it out to the lake and it ran fine other than the low rpm's. I have put in a larger fuel tank, new fuel line/bulb, spark plugs, plug wires, fuel line & filter and have rebuilt the carb. I have checked to make sure both plugs are getting fire and it seems like the coils output is fine. I have talked to a local shop and they just said they would have to start replacing parts to figure it out and I really don't want to just start replacing parts that may not be the cause. Any help would be very appreciated.

Don't rev to 5grand with no load on the motor

It kind of bothered me while reving it up like this but it was in the repair manual in the tuning procedures so I thought it would be alright. I have only done this twice.

Find a new shop. That kind of answer is not ok. Something is causing your issue. Did you rebuild carb yourself? Have you done a compression test?

Yes I rebuilt it myself. It only has one carb and there wasn't much to it. The compression on the top cylinder is 130 and the bottom is 132.

I know it probably doesn't have anything to do with how it runs but did you replace the water pump? If it hasn't been done since 2001 it desperately needs it. Find a reputable shop and get it looked at before you hurt it too badly.

Yes I replaced the water pump.

Found a shop and taking it in next week.