I have the same motor on a 20 Skeeter bay boat. Mine does fine on gas if I keep it at 3800-4000 rpms. I get 3.5 to 4 mpg with a decent load, based on logging my miles on the gps and seeing how many gallons it takes to fill it back up versus the miles ran that day. A 150 4 stroke will get you around 5 mpg at cruising speed. The real difference is at idle speed. The 4 strokes get way better fuel mileage at idle speed, but not a whole lot better at cruising speed. You may get a couple thousand for your motor, and spend at least 10K for a 150 4 stroke. 8 grand is a lot of fuel. It would not be a wise move if the intent was to save money. It would take you a long time to see 8 grand in fuel savings, considering you'll be getting around 20% better fuel economy with a 4 stroke. Your motor isn't the problem, the price of fuel is. Go to Yamaha's website and look at the performance bulletins. You'll be able to look at performance bulletins for your exact hull, and look at it the fuel mileage for both motors at different rpm ranges. They also tell you what load the boat had in it at the time of testing. The bulletins on the website are accurate. One more thing, I see a noticeable difference in fuel economy when I treat my fuel with the starbrite fuel treatment in the clear blue bottle. It's enough of a difference that I use it all the time now, and it treats ethanol and is also a fuel stabilizer.

Not hard to burn 120 worth of gas when gas is around 4 dollars. Since its such a reliable motor I say run it till it dies. You have worked out all the kinks on that old motor. Not a very wise decision to invest in a newer motor which may have it is own problems just to save some money on gas.

For the value of the used motor go to www.nadaguides.com.

thanks guys i think im just going to keep it. I went to academy today and bought some fuel additives hopefully it'll boost my gas mileage

It will help some with fuel economy, but the main reason I use it is to treat the ethanol. The ethanol free stations around my house are out of the way and very tight as far as getting in there with a boat behind the truck. Don't expect a real big difference in fuel economy with the additives. One other thing, try to idle as little as possible. Your motor gets around 1.5 mpg while idling, as opposed to 3.5 mpg or so while cruising at 4000 rpms. Get on plane and stay there as much as possible.

how many rpms u turn wide open and how many rpms is the motor suppose to turn wide open??? check that out!! maybe a lil cup on the prop one way or the other will help with fuel economy, if the rpms arent right!! talk to a good prop shop!!! also maybe raise or lower the motor depending on the rpms??? let us know!!!!

Think of it this way. If a new motor cost 10K, and your motor is worth 2k. That is a 8K difference. Gas at $4 a gallon divided into $8k is 2000 gallons of gas. How long can you run on 2000 gallons of gas?

good point!!! just have to make a decision good or bad!!! i would keep it just check the rpms!!!