1974 6 hp wont pump water at idle. im going nuts.

[2 strokes is all i need]

my neighbour originally had this motor. it has a problem where it wont pump water at idle. he blew the motor because of this. so he had the powerhead professionally rebuilt. total ignition system overhaul, carb rebuild, the works. he also had a new impeller installed. after he got the motor back together with all new parts, it still has the same problem, so he got pissed and threw the motor away. me being a cheap shake i plucked it out his garbage pile one night.

so now i have this great motor, its got top compression,. starts on the first pull, runs like a dream. but it wont pump water and cool the motor at idle. you can run it all day long at half throttle or full throttle and the cylinder head stays at a good temp, but as soon as you go down to idle it overheats. when i say overheat i mean i shut it off at 220F. i measure the temparture with a portable infrared temparture gun so its pretty accurite. besides, if you spit on the head the spit bubbles so it IS overheating.

first thing i thought was maybe its an impeller problem, so i tore the lower end apart and had a look. everything was lined up correctly, including the impeller keyway. i spun the lower unit with my electric drill and it will pump water higher than my head so i KNOW the lower section is good. also the rubber boot which connects the cooling tube from the imeller housing to the powerhead is in good condition.

so next i pull out the thermostat. it looks new. i put it in a coffee cup with water and heat it and sure enough when the water gets warm it pops right open. if i let it sit and cool the thermpstat closes back up. so its not a thermostat problem.

so finally i thought maybe theres a blockage somewhere in the powerhead, but i pulled the cylinder head off and everything looks clean. if i hook up a low pressure pump to the cooling tube which extends down from the powerhead it flows water through the motor just fine.

so whats going on? im freaking out now. im not a newbie to outboards. and 2 strokes are a passion of mine. but this problem is licking my butt. ive been wrenching on motors for a decade now so i almost feel embarrassed to ask for help.


p.s the motors water pickup port is WELL below the water line at idle or when at speed, or when testing it in a bucket.

 

[ezeke]

Re: 1974 6 hp wont pump water at idle. im going nuts.

Are you having this problem with the boat on the water or are you running the motor in a bucket?

 

[ezeke]

Re: 1974 6 hp wont pump water at idle. im going nuts.

Be sure that the water in your bucket is as high as the top of the water pump.

The primary entry for your cooling water is the small screen above the propeller, so when the propeller is turning, it pushes water into the pump. You do not have that advantage with a bucket, so you need to keep the pump itself under water. The pump is not self-priming.

BTW, a lot of the 6 HP motors had upgrades adding the new style water pump kits. It made a lot of difference in my 6HP Johnson. If you still have the cast metal impeller housing, I would recommend the upgrade to a new pump, BRP part 763758.

 

[Vic.S]

Re: 1974 6 hp wont pump water at idle. im going nuts.

Random thoughts:

I have a recurring problem with the grommet at the top of the water tube on a later model but is not the same and the symptoms are not either but could the water be leaking up there?

Could the water tube be leaking?

Re the pump and its depth, the pump is up around the joint at the top of the gear-case so it must be immersed above that joint. That'll put the cavitation plate well under water.

 

[bearkatbrandon]

Re: 1974 6 hp wont pump water at idle. im going nuts.

I had that same problem with an old 15hp johnson, had to use it for a long ride back to shore and it stopped peeing at the end. I tore it all apart, heads and everything to look for some kind of clog. Ended up being a swollen grommet where the motor block meets the lower unit. I was told this can happen when the motor heats up. Hope that helps.

 

[2 strokes is all i need]

Re: 1974 6 hp wont pump water at idle. im going nuts.

when i test the motor on the boat or in a bucket i make sure the impeller housing is below the water level. actually well below the water level.

today i tried removing the thermostat and running without one. it made no difference. it still gets above 220 and i shut it off.

i even ran under power and got about 300 yards out before it overheated and i let the wind bring me back to the ramp.

im starting to think about selling it. its a great motor. just wont pump water. a new tohatsu is nearly the same cost as a mechanic would charge for parts and labour to fix this 35 year old motor. the rubber grommet under the motor idea is interesting, but that seems like a lot of work. it might be more than i am willing to do. im getting frustrated taking the same parts off again and again.

thing is, it runs soooo good. it sits there and idles all nice and smooth. it has good power, starts good. i guess its that whole rock and a hard place thing.

 

[CATransplant]

Re: 1974 6 hp wont pump water at idle. im going nuts.

Hows the intake screen? It's in the little snout right over the prop. If it's pretty clogged, it might not be admitting enough water at idle. It can be replaced with a new one, or cleaned.

Everything else checks out, so that's a likely spot for a restriction on water flow at low RPMs. When the engine's running faster, it can suck up enough water. When it's slow, a clogged screen can block water flow and cause overheating. Take a close look.

 

[2 strokes is all i need]

Re: 1974 6 hp wont pump water at idle. im going nuts.

ok i got angry and pulled the powerhead and the lower end off the motor housing.. nothing looks wrong anywhere. all the cooling ports are clean. i checked the metal tube that connects the impeller housing to the powerhead and it held 60psi of air for 6 minutes so it doesnt leak. i blew 10 psi of air through the motor cooling ports and they all flow freely and dont seem to leak. they are complicated looking so i cant tell if water is suppose to come out of certain holes or not. but water does flow freely through the powerheads cooling system.


if i put the lower end in a bucket of water and spin the main shaft with a drill the impeller housing it will pump water over my head. it actually can pump up to the roof of my house because i put a hose on the impeller output hole and rested the other end on the gutter of my house just for curiosity's sake. i was kind of impressed that it had that much lift. it made me laugh. the pump seems to have a lot of lift, but low volume. although i have nothing to compare it against so that is just a guess. the rubber coupler that connects the impeller housing to the engine coolant tube is in top shape. so i dont think anything is wrong there.

i looked at the intake screen and it is spotless. i even flushed water through the lower end and there are no restrictions. i even want so far as to clean all the ports with a nylon bristled brush that you use for cleaning gun barrels. but its all clean in the lower end, the top end, everywhere.

maybe ill try that updated impeller housing someone mentioned. if that doesnt work, im thinking about taking the aluminum motor to the scrap yard. they are getting 65 cents per pound for aluminum. i might make enough to buy a 12 pack and call it a weekend.


someone please help me. but i have a passion for 2 strokes, espically older ones. i would LOVE to have this motor be reliable and good running. these sort of things tweak my fancy.

 

[locallawoff]

Re: 1974 6 hp wont pump water at idle. im going nuts.

ok i got angry and pulled the powerhead and the lower end off the motor housing.. nothing looks wrong anywhere. all the cooling ports are clean. i checked the metal tube that connects the impeller housing to the powerhead and it held 60psi of air for 6 minutes so it doesnt leak. i blew 10 psi of air through the motor cooling ports and they all flow freely and dont seem to leak. they are complicated looking so i cant tell if water is suppose to come out of certain holes or not. but water does flow freely through the powerheads cooling system.


if i put the lower end in a bucket of water and spin the main shaft with a drill the impeller housing it will pump water over my head. it actually can pump up to the roof of my house because i put a hose on the impeller output hole and rested the other end on the gutter of my house just for curiosity's sake. i was kind of impressed that it had that much lift. it made me laugh. the pump seems to have a lot of lift, but low volume. although i have nothing to compare it against so that is just a guess. the rubber coupler that connects the impeller housing to the engine coolant tube is in top shape. so i dont think anything is wrong there.

i looked at the intake screen and it is spotless. i even flushed water through the lower end and there are no restrictions. i even want so far as to clean all the ports with a nylon bristled brush that you use for cleaning gun barrels. but its all clean in the lower end, the top end, everywhere.

maybe ill try that updated impeller housing someone mentioned. if that doesnt work, im thinking about taking the aluminum motor to the scrap yard. they are getting 65 cents per pound for aluminum. i might make enough to buy a 12 pack and call it a weekend.


someone please help me. but i have a passion for 2 strokes, espically older ones. i would LOVE to have this motor be reliable and good running. these sort of things tweak my fancy.

Gidday,If I understand correctly you put air pressure up the water tube from the water pump to the lower part of the power head and it held pressure.If that is the case that tube is blocked.I would remove that tube and start looking from there.Impellers have been known to disintergrate and the bits blockup that or where it goes into the powerhead.I have put over70lbs thru this to blow out the rubber pieces.Hope this helps from downunder.Locallawoff

 

[F_R]

Re: 1974 6 hp wont pump water at idle. im going nuts.

Sierra made some 6hp impellers that were too thick. Could you have one of those? The fact that it pumps on the drill contradicts that thought but it's still something to think about.

Are you saying that it actually stops pumping at slow speed (no discharge out the back?) Or does it overheat even though it's pumping?

The fact that it cools at high speed says that it is not plugged up anywhere. However, as I remember it, there are two routes the water takes through the powerhead. I'm thinking out loud, wondering if the rebuilder drilled out some passages, upsetting the flow direction.

Also, I'm thinking out loud again, wondering about the head temp. Is the whole head getting that hot, or just hot spots?

If it actually stops pumping at slow speeds, I suggest you put in a new style complete kit and make sure the plate is sealed to the gearcase.

If you want to junk it, drive by and throw it in my front yard.