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Steam out of exaust port

O

oneal

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Any one had problems with 1975

Any one had problems with 1975 25hp johnson picking up water at half to full throttle.

I have new water pump impeller and all new o-rings and seals in lower unit.


Water pickup is at the top of cavatation plate.

Cavatation plate is 2 inches below boat.

I've tried leaving pickup cover off to see if this was restricting water (it wasn't) No trash was pulled in.

Water sprays from exaust port while idleing or
revving up of motor in neutral.

At half throttle to full throttle only steam when in gear.

All info appreciated!!!!
 
"Your water pick-up is in fron

"Your water pick-up is in front of the exhaust out-let behind the propeller, not above the cavitation plate!
If engine is tilted too far out, problems might occur.
If propeller is damaged and cavitating (producing air-bubbles), problems might occur."
 
Thanks!!!

What is the recta

Thanks!!!

What is the rectangular opening( has cover with several little holes) above the plate for?

Isn't water supposed to be spraying from the opening about half way of the exhaust housing all the time?

Thanks again!!!
 
Also the prop #'s are 0120

Also the prop #'s are 012015 MICHIGAN.

A web page calls for a 8.49x11.00 ( I think).

Boat porpoises after it planes out.

Boat is a 14' fiberglass tri-hull.

Thanks!!!
 
"1991 johnson 70hp, above 3700

"1991 johnson 70hp, above 3700 rpm alarms and rpm limiting occurs.engine doesn't seem hot. replaced impeller, same symptoms.what up?"
 
"charles, i would start a new

"charles, i would start a new thread you will get more direct answers.

david, porpoising is usually caused by too much trim.....although i doubt yours has power tilt and trim.

the cavitation plate is a little low............it should be right at the bottom of the boat.

as low as your motor sits you should have no problems picking up water.........unless you have it tilted too far and the water pick-up holes are coming out of the water...............if this is not occurring i would suspect maybe something went wrong during reassembly or you should have replaced the whole water pump......as the housings do wear out."
 
"The 'old' type gear c

"The 'old' type gear cases (without prop-exhaust) should be mounted with the cavitation plate 1"++ BELOW bottom. Too high, You get a terrible exhaust noise and prop slipping problem.
The engine should be trimmed so the cav-plate is parallel to water when running. The plate above is just for water draining."
 
"thanks morton, i didnt know a

"thanks morton, i didnt know about the through hub exhaust thing......well lack there of.

i learn something new everyday."
 
If the rectangular opening wit

If the rectangular opening with a few small holes ( that is even with the top of the cav-plate) is for water drainage then where do i place the ear-muffs for the water supply when testing??

Thanks very much guys!!!
 
"just slide them on the lower

"just slide them on the lower unti below the cav plate,(little round holes/looks like a screen inside)
249876.jpg
"
 
"Charles C. Thompson,

I am

"Charles C. Thompson,

I am new to outboards and I'm a very slow typer on the keyboard. I would post your question and hopefully some of the guys that really know a lot about motors wiil tell you the answers.

A mechanic at a marine parts store told me they didn't know why mine was doing what it was and charged me $75.00 .

I've cleaned the carb., put in a new water pump impeller , Replaced seals and o-rings.

Now I'm goig to set my engine more level and try it out. Wish I knew more.

Hope you get it figured out, mine is driving me nuts. It does the same thing on my other boat."
 
"Charles Harris,

My lower u

"Charles Harris,

My lower unit has a little tube like thing behind the prop, where the little fin that you can turn and adjust is on the lower unit in the picture you posted. except the one in the picture is not on it."
 
"There are specific muffs for

"There are specific muffs for the old gearcase that cover the in-take, but the easiest one is just to use a bucket. Be sure You have water all the way up to the water pump, leave the garden hose running into the bucket.
Bad design or not, it was what was used at that time. Newer casting and machining tools made the through prop exhaust systems possible, and no doubt they are superior in performance in the speeds we are talking about, not racing!"
 
Thanks Morten!!!

Wasn't

Thanks Morten!!!

Wasn't downing the design. Is there any thing I can do to improve water pick-up rate. It takes a few moments to get on plane(quite a few) and I'm thinking this is the reason for my over heating problem.

I really appreciate your help and knowledge!!!
 
I don't think I was the on

I don't think I was the ony one having this problem because there was originally 3 to 4 holes in this cover.
 
Is this area with all the hole

Is this area with all the holes not a water pickup opening?

Do I need to order a new cover with only 3 to 4 holes.
 
"Look at the 'slot' ju

"Look at the 'slot' just behind Your prop - there is the water pic-up. Check that it is not clogged. To renew the insert, take out the screw plug at the bottom and pull out the insert.
The cover plate is no water intake. The more holes You make, the more exhaust and noise You let out. Get a new one from a scrap-engine!"
 
oopps did not read your first

oopps did not read your first post closely enough
i think you have the problem solved
 
oopps did not read your first

oopps did not read your first post closely enough
i think you have the problem solved
that looks like a 1960 era engine
 
"My motor isn't over heati

"My motor isn't over heating now. I dropped it down to first hole (or down close to boat.)

Covered all the holes except for 3 in the cover.

Motor doesn't idle smooth it is really rough ,jerky.

I can get it on plane(motor runs smooth when I back off a little it looses power and falls off plane as if I went to 1/4 trottle. And runs rough again.

I've cleaned carb set low end adjustment (about 1 and 7/8 to 2 turns out.

Plugs are new and gapped @ 30, Points set @ 20 .

Can anyone give me some ideas on what to do to fix?

Thanks!!!"
 
"Back pressure might have chan

"Back pressure might have changed.
Do a de-carb, clean, adjust the carb and re-synch!
Be sure carb does not open more than 99-100% at full throttle.
PS:
Have to go for the next 12 hours, out for an overnight squid fishing contest! (Using my Yamaha 40 Enduro!!)"
 
"Is the ignition plate under t

"Is the ignition plate under the flywheel supposed to have any play or looseness to it?

I can wiggle mine up and down (about 3 to 4 thousandths of an inch. And back and forth in circular motion 1" inch or more.

I've noticed that when it misses or jerks that this plate moves back and forth real quick, also making the little arm with bushing or roller blip the carb throttle a little."
 
"Back again after a night of t

"Back again after a night of thunder storms and little squid!
You might be able to 'wiggle' it up and down as mentioned, due to wear and tear, but it should not be 'spring' loaded for rotation. Plate however rotates when throttle is applied!!
I suspect Your engine might be running lean and back-fires.
If lucky a clean and adjust/synch might do it."
 
"I saw on tv that the squid in

"I saw on tv that the squid in calafornia were eatng all the fish up.
Took flywheel off, coil,points and condensers and cleaned. Reasembeled went fishing had motor trouble.
Are the Seloc manuals accurate?
My motor has 25R75B on the model plate.
But the pictures about the plate under the flywheel doesn't look like mine.
Will take apart clean try new points & cond.
Will break carb down reclean and adj.
What do you suggest on a accurate rebuild manual?"
 
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