1986 johnson 90 hp seahorse..going to 5krpm full throttle ok ?

[johnson426]

Hey guys, my 1986 90hp johnson seahorse outboard is going to 5000 rpm full throttle, is that right ? or should it be going higher ? also can someone tell me exactly which champion plugs to run on my motor ? thanks alot for the help!

[countvlad]

Hey guys, my 1986 90hp johnson seahorse outboard is going to 5000 rpm full throttle, is that right ? or should it be going higher ? also can someone tell me exactly which champion plugs to run on my motor ? thanks alot for the help!

sometimes is tough to get info on certain things because there are so many outboards out there... best place for you to get all this info is in the manual

www.outboardbooks.com

good luck

[Chinewalker]

The general consensus is that your motor will be happier long term if it can peak at 5500-5800. 5000 is borderline lugging, which can result in bad things...

[johnson426]

Yeah, seems like its lugging because I have to hold it at full throttle at 5k to be moving, or else it will just stand up because of the load...how high should I take it up to and be safe ? and what should I do, to raise the rpm ? prop size ? sorry im new into boats..thanks for the help!

[johnson426]

anyone else know the problem ? please helpp

[cougar1985]

anyone else know the problem ? please helpp

what kind of boat?weight?what do you have for prop now?see the boat in my avatar?with my 90 on her and spinning a 21 p prop i will hit almost 48 by gps!now that boat is very light mind you ,500lbs.

[johnson426]

Its an 18ft manatee boat, im not sure exactly how much it weights and the prop size but I will get that when I get home. Should I change the prop to get a higher rpm at full throttle ?

[johnson426]

should I get a different prop ?

[AEROCOOK]

should I get a different prop ?

Too many unanswered questions at this point to answer your question.
First, find out whats on it now.
Not sure what 19' Manatee weighs but to even guess at an appropriate prop, you need to find out. Trim setting can play a big role in engine performance, have you experimented with different trim settings? Is the motor original to the boat? It could be over propped for your boat if it came off of a smaller/lighter vessel.
If you want to get really excellent advice on props, post in the prop forum but be prepared to answer a host of questions about your boat, prop selection is a real science.

[johnson426]

Okk thanks for the help, I will do that!

[ezeke]

All other things being correct, the prop should have a lower pitch to allow you to reach 5800 RPM with your average load.

You may be able to reach that with changes to your set-up, however.

[johnson426]

This is actually my 2nd outboard, I had the same one on my boat but 2 years newer(1988) but it overheated and lost compression so I gave up and bought a 2 year older(1986) but in better condtion. When I first took it out, I noticed it took a while to plain off so I went back and swapped the prop with my old one and it got alot better but I noticed the max rpm im getting to is around 5000rpm and it seems like its lugging a bit

[johnson426]

5800 rpm is safe on a old 2 stoke motor ? sorry im new in boats and I just wanna be safe

[johnson426]

Im gonna try to tilt the motor higher to see if it helps, but how high should I bring it up before its bad ?

[AEROCOOK]

Im gonna try to tilt the motor higher to see if it helps, but how high should I bring it up before its bad ?

Ive been told that to achieve the optimum setting you trim out till the boat begins to porpoise then trim in a little at a time till the boat stops porpoising and leave it there.
Thats the way I do it but others may have differing opinions.
BTW, you have power trim right?

[ezeke]

When the boat is on plane, the A/V plate should be parallel to the water surface and just above it. Under most conditions the A/V plate must be at least even with or slightly higher than the bottom of the boat to do that.

Propping the motor to reach 5800 does not mean that you will run at that RPM a lot, but that you can. If the engine is in good condition, running at that RPM won't hurt it, it's capable of going a lot higher - like 8,000 RPM.

[johnson426]

I have manual tilt on my boat so its a lot harder to adjust since I have to pull the boat out the water everytime to switch the rod to a different positon for differnt trim angle

[johnson426]

Can I hurt the motor from being tilted all the way down and only reving to 5200 max? It takes a lil to plan and feels like its stressing the motor but correct me if im wrong

[kenmyfam]

Can I hurt the motor from being tilted all the way down and only reving to 5200 max? It takes a lil to plan and feels like its stressing the motor but correct me if im wrong

OK, what prop is on it ???
What speed and RPM are you achieving ???
How is it compared to the old motor when it was running well ??
Is the new motor the same shaft length ???
Photos of the motor and cav plate and the bottom of the hull will help.
How many people on the boat ???
Where is the fuel tank ???
Where do you store the rest of the gear you carry ???
You need to know your set up is good before playing with things that cost money.
My 2 cents.

[DJ]

5000 is too LOW, as mentioned. Minimum of 5500 is desired.

How you accomplish that? It can be done several ways.

1. Trim angle.

2. Engine height.

3. Lower pitch prop. One inch in prop. pitch generally relates to 200 RPM, up or down.

[johnson426]

Ok guys I found out my prop size is 13/75x15 and motor is trimmed all the way down(I have manual tilt) I tried 2 people on the boat or 4 people, but the rpm will go to 5200rpm. The only difference I see is with more people it takes longer for it to plain. let me know if anyone can help! thanks

[ezeke]

On most boats, trimming the motor all of the way down will place the A/V plate at a downward angle away from the boat. This will lift the stern and force the bow down, so that the boat plows.

Since you have only manual tilt, it would be preferable to set your thrust rod in such manner that will place the A/V plate on a plane very close to level with the planing surface of the boat. In this manner the motor will push the boat in a straight line, rather than lifting it or forcing it down.

[AEROCOOK]

Ok guys I found out my prop size is 13/75x15 and motor is trimmed all the way down(I have manual tilt) I tried 2 people on the boat or 4 people, but the rpm will go to 5200rpm. The only difference I see is with more people it takes longer for it to plain. let me know if anyone can help! thanks

A 15 pitch prop should allow that 90hp to rev way past 5200 unless the boat is really heavy or there are other issues with the motor it's self. Not sure what an 18 foot Manatee weighs but is it possibly waterlogged? To begin with, I think you should trim it out 1 hole at a time to see if the RPMS come up. Also, have you confirmed that the butterflys on your carbs are perfectly horizontal when the throttle lever it at full?

[johnson426]

When I rev it in neutral, it will go to like 6000 but under load it wount go past 5200. Can someone explain waterlogged ? Im not sure exactly how much it weights either, I tried to look in the paper work but no signs of weight. The motor seems to run strong and I did check the butterfly for the throttle, they open up all the way!

[ezeke]

It's not a good practice to run the motor higher than 1500 RPM with no load - could cause a run-away.

Waterlogged refers to the floatation material in the boat's hull. As the cell break down over time, they are able to hold water which can only be removed by removing the material. The saturated cells add weight to the boat which slows down the boat and disturbs the design balance.