It hesitates between 3000-4000 rpm, tbh there’s far too much

Dear costumer I am reviewing your query at the moment you are viewing this message, please give me a moment to evaluate your problem in detail, you can send me pictures or videos that better describe your problem, also, it is likely that I should ask some additional questions to improve my final answer. The system will offer you a premium service call which has an additional charge to the initial cost of the consultation, but it is not necessary we can continue through this chat without any problem. Thank you very much for trust in just answer.

Dear customer, do you have power loss or just vibration?

Dear customer, thank you for clarifying this, is your boat petrol or diesel? Or could you tell me your model

Dear customer thank you for clarifying this, in the boats the main cause of loss of power are clogged filters, so my main recommendation is that you should perform a cleaning of them especially the air filter, the constant moisture also generates the spark plugs wear faster, so there may be problems in the spark which produces choking sensation at high rpm.

Dear client, I will leave the consultation for another expert to deal with if you feel more comfortable with it.

Hello, welcome. Who do I have the pleasure of speaking to? My name is***** am here to help. I have been in the marine industry for 25+ years and have been a licensed Marine Engineer since 2009. I like to think outside the box and was part of the team that set the UIM Round The World Speedboat Record. I would like to be your requested tech when you have boat issues. I will be happy to help you.

I know that can be frustrating. Hopefully, we can get you back on the water quickly.

You are back in the outboard section. I saw this question yesterday on the board but did not answer because of the lack of detail. I have never seen that type of response above. That is strange. Kind of like a bot was answering or something. Anyway, you have a human now. Only you were asking for a phone call, I don't normally take phone calls.

So we have a 2006 Mariner 90hp that has a flat spot between 3-4K?

There is a lot of text to read through I am trying to make sense of. If this outboard came into our shop we would first put it on a test tank. That is a spark fuel outboard tank and then we would take the boat out and test. The idea is we want to start narrowing down the possibilities. That test will tell us if this is an off-engine or in-engine issue. That gives us direction in our troubleshooting.

Another test we want to do is start the engine, don't rev up or anything, just start and leave the RPMs as low as possible, then go straight to the spark plugs and pull one spark plug at a time and we should hear the RPMs drop out a bit. You'll get the sound difference. If we find a spark plug pull that is not as strong as the others then we have a weak or dead cylinder to track down. This tells us if we have a single-cylinder issue. That can make a flat spot in the throttle response because a missing cylinder then causes the engine to have a flat spot in power output that is RPM dependent vs prop load and we can get "behind the power" in engineering jargon.

Hello Stuart- It's good to meet you. I am sorry about that bot. I have never seen that before.

Does the engine kick in again after 4k or is that all you can get?

Ok, then we really need to do the two tests I listed. We want to run the engine on a test tank, and we want to do the cylinder spark plug pull test. Both will give us direction. Also, we want to pay particular attention to the fuel bulb when running at full output.

Another test we can try to rig up is a clear piece of fuel hose in the fuel system where you can get it. That will tell us if we have a stream of bubbles entering the fuel system somewhere. That will do the same thing, limit our top RPMs and the engine will just sit there not putting out.

That compression is really good for a two-stroke.

Is the 123 the bottom cylinder? That would be normal. The bottom cylinder normally starts to drop compression first, but those numbers are fine.

So what else could it be? Reed valves? It does not sound like that. One carb that is not putting out the clean fuel-air mix. Maybe. You might pull all three spark plugs and examine them. They should all look chocolate brown. If we have a different one we can think about why that is. It sounds like we are not producing the hp we need at the top end and that is almost always not enough push on a single-cylinder to add to the total hp or a fuel restriction that also might be air getting into the fuel system from something as simple as a bad O ring in one of the quick disconnect ends that is feeding a stream of air bubbles. Happens all the time.

One more thing if you are testing tomorrow is when the engine limits out try gently squeezing the fuel bulb and holding pressure for a while, like a minute, just gentle positive pressure, and if we have an air leak that will force the fuel into the carbs and if the engine changes tone in any way we are onto the issue.