How fast should an old Tyee go?

[SDeadeye]

My girlfriend and I recently brought home a 1985 Tyee 5.5 that has been in her family since it was almost new. This is my first experience with owning a boat, so I'm learning a bit as I go. It's been long enough since anyone in her family used it that most of the info I'm wondering about has been long forgotten.

We've had the boat out a few times now, today was one of the first chances I've had to make a nice long run with it though. The waves were maybe 6-8", pretty calm.

This boat has the 3.0L Mercruiser 140 I/O setup, 1.98 ratio outdrive. What should I be seeing for top end? The best I could do was just barely over 30mph at about 3600-3700rpm. Both numbers seem low to me. I don't have the book in front of me but 4200-4600rpm sticks in my mind as the target range. That was with two of us in the boat plus the trolling motor and 2x group 27 batteries up front that I have added recently. The boat got up on plane pretty quick, and I had to do a bit of messing with the trim to get it just right to break 30mph.

[brown1317]

Originally Posted by SDeadeye

This boat has the 3.0L Mercruiser 140 I/O setup, 1.98 ratio outdrive. What should I be seeing for top end? The best I could do was just barely over 30mph at about 3600-3700rpm. Both numbers seem low to me. I don't have the book in front of me but 4200-4600rpm sticks in my mind as the target range. That was with two of us in the boat plus the trolling motor and 2x group 27 batteries up front that I have added recently. The boat got up on plane pretty quick, and I had to do a bit of messing with the trim to get it just right to break 30mph.

Sounds like you need a good tune up. I have a 98 1850 tyee with the 4.3. Limiter kicks in at 4600 rpm and I can do 50 with 23 inch 3 blade prop, 2 guys, light chop. I would expect the 3.0 to hit about 40-42 if it's running right. Now if you've got a bunch of hours on the motor it might be getting a little tired...

[REW]

Do some prop testing.

Pick up two or three different props with different pitches and try each of them - test upwind and downwind, and also record engine rpm.

Also, double check your throttle setting and the opening of the carb. Be sure that if you have the throttle wide open, that your carb is also running wide open. If not, disconnect the cable at the carb, and verify that the carb will open wide open. Then, with no carb connected, insure that if you advance the throttle that the end of the cable will be where it needs to be to insure that the carb or fuel intake will be wide open.

On this rig, with the right load and prop, you should be running at least 4500.

Best wishes.

p.s.
If you have not checked lately, check the condition of the oil in the lower unit. Be sure that there is no water in the outdrive and that the outdrive is fully filled with oil to the top plug.

p.p.s
You can also take the rig to a shop that has a good dyno and have the hp checked in the rig. If not, have the folks at the shop with the dyno do some checking on the engine to verify any issue with a low hp motor.


Best wishes

[SDeadeye]

Thank you, that is all good info! Fun what I've been told, the engine has somewhere between 20 and 50 hours on it since it was fully rebuilt. But again that was probably late 2000's so exact info is hard to come by. I know it needs some carb work just from having old gas sitting in it if nothing else. That's on my winter project list too.

[SDeadeye]

Update - From the real brief look I had at it, the current prop is marked 19P. It's a 3-blade aluminum, I'll have to take it off to see what other markings are on there.

There was a busted up old prop in the garage that I took a picture of when we were looking for spare parts for the boat. The only markings I could make out on that one were 17P and 130. Not sure what the 130 means, if anything.

[REW]

Buy a new 17 pitch aluminum or stainless of the correct size for your rig and you will be good to go.

Also, over the winter, you could tun the engine and then take the rig to a shop with a marine dynamometer and have the rig tested for power. If down on power the shop can do its thing to verify any problems that might be in the engine.

For your setup it is reasonable to expect the mid to high 30s, maybe the low 40s.

Best wishes.

[REW]

https://forums.iboats.com/threads/ho...r-have.454594/

[Wrktfsh]

You May have waterlogged flotation foam too. That boats been around the block a few times being a 1985

[last chance]

it may need to be trimmed up to raise both speed and rpm. if this doesn't get you to where you want to be you might try a 17p prop which should raise the RPMs about 400 but it may not help your speed but it will help your hole shot a lot.. but before buying anything check to make sure the carb is wide open when the controls are wide open. and be sure to trim it up as far as you can but not far enough to start having problems. just trim it up a little at a time as long as the rpm raises and the speed raises also. if the RPMs goes up but the sp[eed doesn't you've gone a little too far, so trim it back down some.

[SDeadeye]

I did play with the trim a bit the last time we were out. There was a couple mile run back to the ramp and it was nice and calm so I was bumping the trim up a little at a time and watching the tach and GPS speed, trying to find the sweet spot.

Looking down into the carb, it seems like I'm getting to fully open. A good cleaning or carb rebuild is on my winter project list. I'm still working some of the old gas out of the system too I'm sure. I also want to replace the old loose red carpet on the floor, so when I do that I'll take some cores of the foam and check for water. It's been stored inside for a good portion of its life but I'm sure in 37 years is been in the rain more than once.

I did order a 15x17p Black Max prop and got that put on the other night. Hopefully I can give it a try this weekend.