1989 90 HP Johnson Prop Help

[JOSHinIA]

Okay, I just bought this boat and it's my first step into what I would consider "real" boats. I've used a little 12 foot v-bottom fishing boat with a 4 hp Johnson on it for the past five years and just recently found myself a nice 16 foot bass boat (1989 Bass tracker 1600 TF) with a "Tracker" Johnson 90 HP on it. Anyway, today was the first chance I had to take it out and really open it up to see what it would do.

Here's what I found:

1: The boat seems to take a LOOONG time to get up on plane, about a 1/3 of a mile (roughly).
2: As I'm waiting for it to plane, the RPM's (at WOT) run about 3000, but as soon as it planes, it jumps to 5000.
3: Then once it's on plane, it starts to bounce pretty violently (I don't really know what would cause this)

The current prop that's on it is a 13.5 x 20 stainless 3 blade.

I would like to switch to an aluminum prop, which I know throws another variable in the mix, but would switching to something like a 17 or 18 pitch prop fix problems 1 and 2? Or is it something else that's causing those problems?

Also, I have a feeling that problem 3 isn't the prop, so if someone could point me in the right direction to fixing that, it would be great.

If there is any info I missed, let me know and I'll do what I can. Any help is appreciated.

Thanks, Josh.

 

[BonairII]

Re: 1989 90 HP Johnson Prop Help

Probably a good time to weigh your boat....it may be waterlogged.

The boat bouncing is "porpoising" trim the motor down more.

Don't buy another prop until you(we) confirm that your motor is running properly...and that your floatation foam isn't waterlogged(making your motor struggle to get boat up on plane).

 

[JOSHinIA]

Re: 1989 90 HP Johnson Prop Help

Thanks for the quick reply.

What if I find out the boat is waterlogged? Can it be fixed? What would cause it to happen?

If the "porpoising" is fixed by trimming the motor down, then I've got yet another problem, that is with the trim all the way down. Does that now mean I need to unmount the motor and move it down another notch on the transom bracket?

Again, thanks for the help.

Josh

 

[BonairII]

Re: 1989 90 HP Johnson Prop Help

If the boat is waterlogged....you're not going to be happy cause you'd have to strip the boat down to the hull and totally restore the boat.

If your motor has manual trim, just put the thrust rod(pin) in the hole closet to the stern of the boat(the leg of the motor will be hugging the back of the boat).

In regard to motor 'height'....the motor should be mounted so that the anti-ventilation plate is riding on the surface of the water at WOT.
You won't be dealing motor height until we figure out why you can't plane the boat easily.

With the 90hp, you should be able to jump up on plane very quickly.

Does the stern of your boat sit unusually low in the water when you're not moving?

I'm guessing the motor is the main culprit here(but you still may be waterlogged also). A good running 90hp should get even a heavy boat on plane much quicker than it's taking you.

 

[JOSHinIA]

Re: 1989 90 HP Johnson Prop Help

When the boat is in the water, it seems to sit pretty level. It doesn't seem unusually low to me anyway.

The motor does need a new impeller because I found the pee stream is kind of pathetic. Though I know that isn't causing the problem...Could it be as simple as rebuilding the carbs?

Also, the motor is as far down on the bracket as it can go anyway, and the rod is on the lowest setting...

Thanks, Josh.

 

[steelespike]

Re: 1989 90 HP Johnson Prop Help

We need the wot rpm and speed by gps.
Usually the foam under there floor becomes water logged from poor storage.On the trailer letting it sit with snow or water for long periods. Or sitting in the water with water in it for long periods.
If it is water logged you may get a constant trickle of water to the stern with the boat on a trailer with the bow raised.
Are you mechanically inclined?
Check that the throttle opens all the way,do a compression check,Confirm it is running on all cylinders.
Be sure the link and sync is right. (that the carb is opened at the right time as the stator advances).
Be sure the timing is correct and advancing as it should.

 

[JOSHinIA]

Re: 1989 90 HP Johnson Prop Help

I am pretty mechanically inclined, problem is I just don't know a whole lot about outboards. I've worked on smaller 2 strokes before, but nothing with so many other do-dads hanging off of it. I know how to check for compression and spark, that's pretty simple. It's the "link and sync" I don't know how to check, does the motor need to pulled apart to an extent to check it?

Here is a couple pictures of the boat I took today to see what you guys think:





Thanks, Josh.

 

[JOSHinIA]

Re: 1989 90 HP Johnson Prop Help

Went through and checked compression and spark. Both were good, compression of about 112 PSI on all 4 cylinders.

I've been doing a bit of reading and found that if the anti-ventilation plate is too low in the water it can cause too much drag on the boat and cause problems similar to mine. I checked the location of the plate relative to the hull and found it to be nearly 4 inches lower. Does this sound reasonable? I can see where a previous owner lowered the motor down one hole from what appears to be the factory placement. With the current placement, the top of the transom bracket on the motor sits directly on the top of the transom, if I decide to raise the motor back to factory height, do I need to make up a shim to go between the two so I'm not putting the weight of the motor on the 4 mounting bolts alone?

Thanks for the help, hoping someone is willing to help me out.

Josh

 

[BonairII]

Re: 1989 90 HP Johnson Prop Help

Your anti vent plate should be around 1/2"- 1" ABOVE the keel line(on most boats anyway). The plate should barely ride on the surface of the water at WOT. If you're 4" LOWER than the keel then you need to raise the motor alot. Sounds like you have a 20" motor on a 15" transom.

It's perfectly fine if the motor is hanging on only the bolts(unless you have a bad transom). My 75hp hangs a few inches above the transom edge. If it bothers you, just put a wood/aluminum shim in so there's no gap.

 

[JOSHinIA]

Re: 1989 90 HP Johnson Prop Help

Well now's when I get to tell everyone I'm an idiot...:facepalm:

Turns out when this motor is lowering after coming off the trailer, the speed it moves slows way down when it gets to a certain point. Stupid me thought that was as low as it was going to go because I didn't look close enough to see it was still moving. We realized this last night when we were playing with it out of the water. So today we took it out and made sure it was ALL the way down and sure enough, it planes out fine. But I still think I need to change pitch on the prop.

Since I don't have a GPS I can't get you the speed, but it wasn't slow by any means. Once I get it up on plane and raise the trim up a little, I'm running around 4800-5000 RPM at WOT. I'm thinking if I go down to a 18 pitch, that should raise my RPM by 400 meaning it should run 5200-5400 RPM.

Sorry about wasting everyone's time...Wish I knew better when I started.

Thanks, Josh.

 

[steelespike]

Re: 1989 90 HP Johnson Prop Help

Going from ss to al can be unpredictable. It is logical to go to a lower pitch.
While the al may do well it isn't likely to perform like the ss. with less pitch it may have good hole shot
but likely lower top end.I think you'll find you have more choice in an odd number pitch you might consider a 19' or 17" pitch.
You could have the 20 repitched or have some cup removed.

 

[JOSHinIA]

Re: 1989 90 HP Johnson Prop Help

I assume since aluminum can move and deform more under load, I would be best off going to a 19 pitch over a 17? I'm afraid if I try going down to 17 I could start going over 5500 rpm which, from what I've read on this motor, is too high.

 

[steelespike]

Re: 1989 90 HP Johnson Prop Help

Yes there is a good chance it could over rev with a 17.
a 19 is a safe bet to gain a little rpm and maybe better hole shot.
top end will likely be less.
With an rpm range of 4500 to 5500 you are well within range.

 

[JOSHinIA]

Re: 1989 90 HP Johnson Prop Help

Sounds good. It seems I can only find a prop that's either 13 or 14 inches in diameter, does it make a difference if I go one way or the other? Also, what is a good brand to go with for an aluminum prop?

Thanks, Josh.

 

[JOSHinIA]

Re: 1989 90 HP Johnson Prop Help

Anybody willing to help me out with my two questions above? I'm hoping to get a prop ordered soon.

Thanks, Josh.

 

[etracer68]

Re: 1989 90 HP Johnson Prop Help

http://boatpropellers.iboats.com/Jo...-132-19_Propeller/86/18339/?*******=862346975

The above link, is what I would get.

 

[steelespike]

Re: 1989 90 HP Johnson Prop Help

http://boatpropellers.iboats.com/Jo...-132-19_Propeller/86/18339/?*******=862346975

The above link, is what I would get.

I agree the Solas props have a good reputation.

 

[JOSHinIA]

Re: 1989 90 HP Johnson Prop Help

Seems like I looked everywhere for a 13.5" diameter...Oh well, thanks for the help guys. I'm going to get the prop ordered and let you know how it works out.

Josh

 

[JOSHinIA]

Re: 1989 90 HP Johnson Prop Help

The new prop came in today, so we put it on the boat and took it out for a spin. I definitely noticed a difference between the props as far as hole shot and being able to stay on plane at lower rpm's, but I'm sort of confused about my WOT results. I was expecting an aluminum prop with 1 inch less pitch to give me around 2-300 increase in my rpm's, funny thing is it turned out to be about the same. I'm running about 4800-5000 at WOT just like the stainless. I guess if my suggested range is 4500-5500 RPM this prop will work good, but I'm just baffled at the fact this aluminum prop is performing like it is compared to the stainless one I just pull off.

Anyway, thanks to everyone who helped me out.

Josh