I need help!!! I have a 1986 25 mercury xd outboard it idles great and then when i give gas it goes and then dies (almost like its not warmed up). It doesn't want to run at full throttle or in gear for very long. The only way i get it to run for a little bit in gear is when messing with the choke. However, when i put the muff on it with the hose at my house it runs fine and will run at full throttle. I'm guessing that it has something to do with the resistant of the water when running on the lake. Any ideas?

Thanks