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Yamaha 200HP carb issue????

:( I have a 1999 Yamaha 200HP carb engine.At the end of last season, it began not making full power.It would reach 4700 R's instead of 5400R's WOT.I have checked the compression of the cylinders. All 6 are at 120 psi.I have replaced plugs, fuel filter, water separator, fuel pumps, rebuilt 3 carbs, replaced stator. When at idle, fuel spits out the exhaust and the engine runs rough.No signs of misses or knocking present.All cyclinders are same temperature.I have spoken to my local Yamaha shop and they are a bit puzzled, but if I bring it in to them they will be glad to fix it.My guess is that they will systemically replace parts until it is fixed, which will cost me a fortune. If anyone out there has any suggestions, I would appreciate it. I will be on the boat working on this tomorrow morning.Thank you
 

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It sounds like you have thrown a lot of parts and money at it and not been able to fix the problem. Sometimes when it gets to a problem that is difficult to trouble shoot, it would be cheaper in the long run to have a competent repair center look at it and give you an estimate for the repair. If you think that your dealer is going to just throw parts at it, you need to look for a new facility. Good trouble shooters test parts and verify they are bad before replacement . Here are some ideas for you to take a look at.

I did not read that you actually took a fuel sample ? You need to verify if you have any contamination in your fuel? Spin off your boat filter and dump it in a clear jar. Next you need to look at each cylinder with a timing light and verify the strobe light is flashing the same on each plug wire. It is recommended to perform this under a load (especially where you are having the run ability issues.) If these look good than I would proceed to the carbs. Run the engine at idle and remove the air box, you want to look for any carbs dripping or spewing gas out of them. Also verify that you don't have an issue with sync and link. That engine has a passage in the carbs that can get contamination caught between the inlet and needle seat. It is usually cleaned out best by an ultrasonic cleaner. (material can get suspended in the fuel and limit the fuel that is getting to the float bowl. You mentioned carbs were rebuilt? Was every gasket,needle,seat and float replaced? If not replace them. If you have the carbs off again visually inspect the condition of the reed valves. You could have fixed your problem by replacing one of the components mentioned in your post , but while the engine was running bad it could have lean sneezed or backfired and broken a reed valve or caused a intake or reed box gasket to fail. Good luck , let us know how you make out.
 

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King Marine is correct. The "poke and hope" method of troubleshooting can get expensive.

One thing common with Yamahas is trash and debris that gets lodged between the fuel inlet passage and the float valves, floats around and restricts the small holes in the float valve seats. Less fuel is delivered to that cylinder and you get a loss of power only at high speeds. Keep running that way and you will get to buy a piston and related parts.

A quick check is to remove the air box cover and look inside each carb bore. You will see a completely different fuel flow out of the main nozzle if there is a fuel restriction. Don't run the motor without the cover for long or at high speed for long because the engine may be on borrowed time.
 

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Have Tried Running Under A Load With The Cowling Off? I Had A Motor That Drove Me Crazy. Come To Find Out One Of The Spark Plug Leads Was Shorting Out On The Cowling Lock Assemble. It Ran Great With Cowling Off!!!!!!
 
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