1984 35hp Johnson

cleve

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Friend of mine bought his old boat back from the guy he sold it to. Has a 1984 35hp Johnson on it.
The guy told him the motor would start up and idle great, but wouldn't run under a load.
So, my buddy gets it home and cranks it right up, and notices there's no water coming from pee hole, so he shut it off.
He decides to check compression. He said he got 140 psi on both cylinders, but the pressure dropped down to 60-70 psi almost immediately. Does this mean anything? He has it in his mind, that the guy ran it hot and toasted the cylinders, but I wouldn't think it would fire right up and idle like a champ?
 

Joe Reeves

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That's not a engine cylinder problem..... that's a compression gauge problem. The cylinder will drop the pressure due to piston blow by, gaps in the rings,etc. It doesn't stay there forever. The compression gauge on the other hand has a seal (some a set screw seal... others a tire like valve) that retains the pressure in the gauge.
 

cleve

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That makes sense. I don't know what gauge he used of how he did the test. But knowing him, he probably borrowed a junk tester and/or didn't know what he was doing LOL!
I figured it can't be all bad, if it runs/idles like he says.
 

Joe Reeves

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You say that it wouldn't run under a load..... doesn't mean too much to me, however, if you mean that it wants to dies out when the throttle is increased, that's normally due to a clogged high speed jet that located way in back of the carburetor drain screw.... horizontal, bottom center portion of float chamber,

Carefully clean it with a piece of single strand steel wire.
 

cleve

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I'm not sure what he meant by not running under a load, but my thought would be like you described, probably a carb issue. I'm going to help him put the impeller on next weekend and I'll get more details.
 

cleve

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We put a new impeller on today and still no discharge from tell tale. The discharge hose is not clogged.
I've put a few impellers on in my life, so I feel pretty confident the impeller key was in place, the fins were bent clockwise (housing upside down same as old impeller which hasn't been changed in 6-7 years), copper tube was inserted properly when putting lower unit back on.
Ran it maybe 1-2 minutes and revved RPMs and still no water. Some spray out of the exhaust ports, but normal IMO.

By chance, will pump need to be primed, like in a barrel? Would a stuck thermostat cause no discharge? Any thing we're overlooking?
 

F_R

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Are you running it in a barrel? If so, it must be deep enough to submerge the pump before starting. If you are running it on muffs, you cannot test a water pump that way. The pump only allows hose water to pass through.

It should pump and discharge water any time it is running, regardless of thermostat status.

You say it is spraying out the exhaust ports. That makes me think the water is circulating, but the tell-tale is plugged. But be sure, and don't burn it up.
 

cleve

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Are you running it in a barrel? If so, it must be deep enough to submerge the pump before starting. If you are running it on muffs, you cannot test a water pump that way. The pump only allows hose water to pass through.

It should pump and discharge water any time it is running, regardless of thermostat status.

You say it is spraying out the exhaust ports. That makes me think the water is circulating, but the tell-tale is plugged. But be sure, and don't burn it up.

Sorry, forgot to mention we had it on muffs. He called me earlier and said he ran it in a barrel but still not peeing. He said water line was above the AV plate. He also said it would pee on muffs when he owned the 1st time. The tell-tale is 100 % definitely not plugged, we pulled the line off and I ran wire up into whatever its called the line connects to. Even ran without the line.
May have to pull lower again and check the assembly again.
 

Joe Reeves

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I have no idea what a AV plate is... but... if your friend is talking about the cavitation plate just above the propeller... that's not good enough.

The water pump is atop the lower unit... the water pump IS NOT self priming.

The water level MUST be above the water pump... the water must be about 4 to 5 inches above the joint where the lower unit meets the long exhaust housing so that the water pump is submerged in the water..
 

cleve

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I have no idea what a AV plate is... but... if your friend is talking about the cavitation plate just above the propeller... that's not good enough.

The water pump is atop the lower unit... the water pump IS NOT self priming.

The water level MUST be above the water pump... the water must be about 4 to 5 inches above the joint where the lower unit meets the long exhaust housing so that the water pump is submerged in the water..


AV = anti-ventilation plate, or anti-cavitation, or whatever the ridge/plate/platform above the prop is called.

Just curious to why the water level needs to be so high versus just over the intake? Is it head pressure?
 

oldboat1

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As indicated, not self-priming. Bottom line is that the motor may suck in air and water and destroy the impeller or overheat the engine, or both. And the bonus is.....you can't tune the motor without back pressure. Lake is best, but dunking the leg deep enough to get it half full of water can give you a chance -- provided the tub is big enough to let you run in gear at idle or fast idle.

Main thing is operating temp. Over 160F (too hot to touch) is too hot. Consider pulling off the l.u., and stepping down a hose to fit the copper water tube, then run some water up there from the hose (low to med pressure). I wouldn't run the motor that way -- just try to clear any blockages. (Tell tale is a fine place for mud daubers or spiders, or salt build up if you have a salty.)
 

Joe Reeves

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Oh, Okay.... Since 1960, we've always referred to that plate as the cavitation plate. I thought AV might have been an Alien Virus :).

The water pump is atop the lower unit... the water pump IS NOT self priming.

The water level MUST be above the water pump... the water must be about 4 to 5 inches above the joint where the lower unit meets the long exhaust housing so that the water pump is submerged in the water.

Otherwise the pump draws air.... When underway, water is forced to the pump via the forward motion as the engine raises to a higher level.
 

valvebounce

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Sounds like,as said above,you are not deep enough in the water.You could check your stat,it may have blocked with crap,with the stat out you could backflush with a hose or just pour water in and check if it comes out of the pee hole.If the copper pipe inside the leg has no blockage,and the pump and impeller are ok,there could be a blockage in the casting where the stat sits.I have had some success in the past by running the motor in a tub and adding a strong solution of washing up liquid,not conventional I know,but it works.
Sounds like your cutting out problem is a gummed up carb,if the motor has been stood with fuel in the carb,the fuel will have evaporated and left 2 stroke oil in the bowl.This will have got in the jets and probably gummed up.Sounds like you need to clean the carb with carb cleaner.
 
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