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My Yamaha 150 jet I just bought will run 5,000 rpms for about 30 seconds then it jump down to 4500rpm and stays there no hesitation. Fires right up idles great I don't think the motor has 100 hours on it it looks brand new. All compression is 120 on every cylinder. Had bad gas in it where it sat for years. The guy said he just put new fuel pumps on it. I changed the spark plugs and cleaned the carbs the best I know how took them apart and soaked them then blew them out with air compressor. Fuel bulb seems hard tried pumping it when running no change. It also has a auxiliary fuel pump I changed that as well. I've done everything I know to do. Any help appreciated thanks