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]

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

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]

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

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]

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

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]

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

anyone else know the problem ? please helpp

 

[cougar1985]

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

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]

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

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]

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

should I get a different prop ?

 

[AEROCOOK]

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

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]

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

Okk thanks for the help, I will do that!

 

[ezeke]

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

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]

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

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]

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

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

 

[johnson426]

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

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]

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

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]

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

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]

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

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]

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

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]

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

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]

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

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.