New xp 200 need help

[wideopen23]

I just bought a 1989 evinrude xp200. I have it on a 1976 18.5 foot southwind. I had a 1976 evinrude 200 on it before but was getting very old and tired. The big diffrence I have noticed besides being extremly faster is that the bow porpuses more now with the new motor than with the old one. When I am running at just a cruising speed it acts like the motor is trim up a bit, but the motor is all the way down. I mounted the motor in the same place as the old one. ANY help would be greatly appreciated.
Thanks,
JC

[snappertapper]

i would guess its because the motor is a little fresher than the other one

[Skaterfast]

Different lower unit?If you mounted the motor in the same place that doesn't mean the prop shaft is in the same place.Same prop??What's the weight difference between the two motors?

[wideopen23]

Iam running the same prop and I have measured the length of the lower units and they are the same. As far as I know the motors should weigh the same but I have no idea. Is there some where I can check?

[wideopen23]

Iam running the same prop and I have measured the length of the lower units and they are the same. As far as I know the motors should weigh the same but I have no idea. Is there some where I can check?

[snappertapper]

they weigh the same, same design

[wideopen23]

Thats what I thought the only diffrence is the cowl on the new motor is a bit bigger,.,,,

[HavasuBarney]

Genrally porpoising is due to a weight distribution problem. What happens is your bow lifts but the prop is unable to maintain the lift, due to to much weight up front, not enough set back or even the wrong type of prop, then the bow falls off, then lifts again.
First thing I would try is moving everything you can either out of the boat or to the rear.
You want all your weight in the back.
Then test it.
Next I'd look at a prop with more bow lift, say a chopper, if your currently running a chopper try one with more cup in the blades.
What type of prop are you running?
If your still having a porpoise problem then it might be time to lower your motor to get more bite with your trim or move your motor back through more setback.
Every tunnel is going to have a range where it will porpose, there's a point just before the boat is packing enough air to carry the boat where it will fall off.
What speed does the problem begin?
What height is your propshaft in relationship to the bottom of your boat?

[wideopen23]

Unfortantly I dont have a tunnel wish I did.
But I am running a 4 blade stainless 23 pitch.
It doesnt purpose so much when running top end speeds it doesnt it more around mid range 30 to 40 miles an hour. I will try moving more weight to the back of the boat and see what happens. I will also measure the distance from the bottom of the boat to the prop. I will have to get to you on this I appreciate the help. I owe you a beer. You might actually know a couple of my friends down in havasu. Richie that owns lakeland and Tony Beck from Walts.
Thanks again,
Justin

[wideopen23]

Unfortantly I dont have a tunnel wish I did.
But I am running a 4 blade stainless 23 pitch.
It doesnt purpose so much when running top end speeds it doesnt it more around mid range 30 to 40 miles an hour. I will try moving more weight to the back of the boat and see what happens. I will also measure the distance from the bottom of the boat to the prop. I will have to get to you on this I appreciate the help. I owe you a beer. You might actually know a couple of my friends down in havasu. Richie that owns lakeland and Tony Beck from Walts.
Thanks again,
Justin