Outboard water pumps

Submitted: Saturday, Sep 05, 2015 at 21:08
ThreadID: 130194 Views:2246 Replies:5 FollowUps:4
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I've just acquired a 8 hp Yamaha and have been using it for the last 2 days. The motor ran very well and water pump telltale ranged from slow stream to fast stream when at full throttle. On returning home yesterday, I ran the motor in a drum of water up to the usual mark and found the motor not pumping water from the telltale. I bought a new impeller and installed today as old one was pretty ordinary but still in one piece with no bits missing. I still have the problem of no telltale, though when I put my finger on the end of it, air was being pushed out of the telltale. With the motor off, I have ran water and compressed air from the telltale and it comes out at the water intake near the propellor. Has anyone experienced this problem before? I have been googling furiously but haven't really come up with much.

Your help appreciated.

regards Kevin
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Reply By: mack c - Sunday, Sep 06, 2015 at 02:09

Sunday, Sep 06, 2015 at 02:09
Hi Kev.

DOn't know where u live but up here the mud wasps love building nests in small places, we mostly carry a length of light wire in tool; kit to poke it out.
Run the motor for a minute or so.
Is the water that comes out round the prop getting hot (not warm)? If hot you have problem.
If just warm/warm. it could be a blockage is working like a 1 way valve.
Run some wire up the hole while running motor. Wiggle it round if you feel anything.
should blow it out.

The tell tale is only to let you know water is flushing system.
If system running warm it'll be no bug deal.
Is impellor on shaft solid or can it rotate by hand?. You got a problem. did you replace stainless sleeve? with impellor. Some do, some don't.
If no obvious blockage and running hot or impellor spinning on/with shaft.
Take it to mech. Don't ask blokes like us "users" on here. We could cost you with our advice.
Have fun
AnswerID: 590024

Follow Up By: mack c - Sunday, Sep 06, 2015 at 02:11

Sunday, Sep 06, 2015 at 02:11
If cover plate over intake. remove and make sure nothing in there.
FollowupID: 858032

Reply By: glids - Sunday, Sep 06, 2015 at 09:49

Sunday, Sep 06, 2015 at 09:49
I keep a short length of 2mm dia whipper snipper cord in the boat to clean out the telltale - stiff enough to poke, flexible enough to go around corners, plastic so it won't corrode or do damage.

As to your exact problem... no, can't be sure. As suggested, take it to a pro. I have a local service guy that doesn't charge for quick advice on the assumption that I am likely to go back for a more major job.

Good luck,
AnswerID: 590030

Reply By: Keith H7 - Sunday, Sep 06, 2015 at 10:16

Sunday, Sep 06, 2015 at 10:16
There is a Thermostat ,this may be the problem.... you can get away with not replacing it depending on different factors.... Google up the manual http://www.yamaha-motor.com/assets/service/manuals/1/lit-18626-06-91_1392.pdf

AnswerID: 590032

Reply By: Iza B - Sunday, Sep 06, 2015 at 14:23

Sunday, Sep 06, 2015 at 14:23
Did you run it long enough in the drum of water for the thermostat to open? At idle, my 15HP needs nearly a minute before the tell tale shows.

AnswerID: 590039

Follow Up By: mack c - Sunday, Sep 06, 2015 at 21:05

Sunday, Sep 06, 2015 at 21:05
My 15hp on rooftopper.
I use a flushing device over intake holes.
Telltale starts flow withing 2 or three seconds of starting motor.
Most do that I've had over the last 50+ yrs or so.
You have a garden hose to ffill drum. Put flusher on end and do motor that way. Much more efficient.
just don't walk away while it running in case flusher slides/shakes of intake and cooks motor.
FollowupID: 858045

Reply By: kcandco - Sunday, Sep 06, 2015 at 18:42

Sunday, Sep 06, 2015 at 18:42
Well I have finally got this problem sorted. On the up side I'm quite good at taking the bottom end off the motor now and even putting it back on, including connecting up the gear selector rod.

Thankyou to everyone for your help. I think the problem was a combination of 2 factors. Firstly when assembling the pump housing, I managed to put an extra gasket in. I think this may have altered the action of the pump. Secondly I experimented with the depth the motor was dropped into water. I found that over the intake up to the first fin on the leg did not work. However if I dropped the leg lower into the water, water started to pump. Looking at how the outboard sits on the boat, I have come to the conclusion I had it too far up in the water. 50mm makes all the difference. I assumed that if the intake was below water level all would be fine, but it appears this is not the case. I now have a really good stream of water coming out the telltale. I am going to get a proper drum to run the outboard in and do some more testing. Incidentally I was worried I may have damaged the new impeller, but when I assembled it I smeared it with rubber grease. The impellor looks perfect despite much info telling me the impeller should be damaged from running dry, even though for a short period of time.


regards Kevin
AnswerID: 590048

Follow Up By: V8 Troopie - Sunday, Sep 06, 2015 at 20:03

Sunday, Sep 06, 2015 at 20:03
Why bother messing about with a drum? Surely an outboard flushing attachment would be much easier. And, you can use this at some ramps to flush the outboard there.
FollowupID: 858042

Follow Up By: mack c - Sunday, Sep 06, 2015 at 21:17

Sunday, Sep 06, 2015 at 21:17
Hmm Gasket wouldn't do much good. But Cav plate should be about an inch or so BELOW bottom of tinny in most cases. Sometimes more.
Normal 15in transom cutout suits motor clamp depth. Drop motor to sit on aluminium and tighten clamps. Mine a 20 in. Does same thing.
Only some bigger motors when you racing etc do you play around with wedges.

Flush motor after EVERY trip if in salt. and replace impellor EVERY season. Regardless. (cheap insurance).
Carrying the old one or new one as spare. along with spare plugs and a file for when you scrape/snap off the bottom plate on gearbox. We all do at some time or other.
I popped a gearbox of a 30hp yrs ago in Coorong, coral bar, shallow water 25+ knots.
Thank god for Johnno 3 1\2 hp reserve.
we about 25miles from ramp at 3 in morning.

Some impellors come as a single item some come as a kit. or choice of. every coupla yrs if kit avail. Buy one. the salt corrodes everything and stainlesss sleeve makes it work better.
FollowupID: 858046

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