15hp exhaust & water leak…why?

[fleetwin]

Did you replace the upper water tube grommet when you had the powerhead off?

[johnyrude200]

The upper water tube grommet was OK, intact. I ended up taking the motor out on my test boat and running it. It ran totally fine and did not overheat. I couldn’t help but notice that these ’74-76 models throw almost no water at idle through the blubber hole (Pre overboard water indicator models), but at mid to high throttle you’ll see it gushing out like a hose. I guess the newer models behave in a similar manner though, >just thought of that<.

For whatever reason, it seems that some motors have a hard time pulling water into them in my 275 gallon test tank, particularly the motors with the thru-hub exhaust. I think they are throwing so much air into the water that it is creating an air pocket and a churned up soup of water and air bubbles.

However, I did have a 3hp JW a fews weeks ago that had the same problem. I had the motor aimed dead center of the pool, and it kept overheating erratically. Then I turned it about 70° to the left and allowed the water to start swirling around and it ran totally fine (cold, if anything). This was, of course, after I had torn it apart 3 times, replaced gaskets, impeller, etc.

There doesn’t seem to be any rhyme or reason for when this situation occurs in the test tank. I haven’t observed any trends yet across generations, model types, or HP ratings.

School of hard knocks as Frank Robb would say…and by the way, I haven’t seen him on here in some time. Anyone know if he’s OK? 😯

[fleetwin]

So the cooling system is OK then? And yes, the early 9.9/15s don’t show a lot of water coming from that relief hole, especially at idle, more of a fine spray. They do seem to expel more water out of there at higher speeds like you mentioned though. I’m guessing this is because the exhaust housing fills with water due to more volume/pressure from the water pump at higher speeds, the excess blows out of that relief hole.

[johnyrude200]

Turns out it was A-OK, but the motor couldn’t pull enough water through at idle or low RPM in a test tank. On the boat, totally fine. In the test tank, at mid to high range, the cooling system worked fine.

I’m still wondering why this was going on because I tore the whole motor apart looking for the smoking gun, but I didn’t find anything. I double and triple checked all water passages, and what made me question things is because I had just worked on another motor of the same model year a week previous and it pumped water at idle like a water hose.

I’m writing this off to the inconsistent quality of the ’74-76 models. Not sure how a motor can run under load on my boat at WOT for 5 mins straight and run cold by all accounts (120° at the top of the cylinders, cylinder head 115-125°), but overheat progressively in my barrel at idle. And it pumped like a hose when underway at mid to high range, but basically just the ‘mist’ you mentioned at idle or in neutral.

Recently had a customer bring in a ’74 evinrude, and it is obvious it has some of the ‘upgrade/recall’ kits installed (different cylinder head that is primer red). Motor starts on 3 pulls dry/cold, but it’s dying off with anything over idle.

[fleetwin]

I am confused also because you are reporting test tank cooling issues that are opposite from the normal woes. Engines usually cool OK at lower speeds in the test tank, cooling gets messed up at higher speeds in test tanks due to aerated water. At this point, I wouldn’t worry about the cooling if everything is OK while running on the boat. In actuality, the early 9.9/15s had fewer cooling woes than the later models, there were no grommet issues on these early engines (unless/until someone replaced the original style grommet with the flawed newer design). The only thing I remember happening was with the original aluminum/SS impeller housings. The salt water would work its way between the aluminum and SS and actually crush the SS liner inwards which usually led to impeller damage/spun hubs and loss of cooling. Needless to say, this problem is solved when the water pump is serviced and the newer plastic/SS housing is used. These engine don’t have a cooling telltale which can lead to confusion though. There is very little cooling water escape from the upper exhaust/cooling relief hole when you first start the engine. You will see a fine spray as the level of water rises inside the exhaust housing or when the thermostat opens.
Jeez, these old beasts are seeking you out! The latest 74 model that found you may just have a partially plugged/dirty high speed jet causing it to falter/die out at higher speeds. Please don’t assume the worst and rip into the ignition until you have run the engine and confirmed there is an actual ignition fault. What spark plugs are you using in these engines? I believe the latest champions are the UL-81J, or UL81C. Some guys report better performance/plug life with NGK plugs, but I don’t know the number/style they use.

[johnyrude200]

All good points. And I agree, these 74-76 models are haunting me right now (I should be THROUGH with them for the near future by the end of this week though…thank god…worked on about 7 of these 9/9/15’s the last 3 weeks and am ready for a simple 6, 9.5, or the good ‘ol 18-20-25’s).

I actually just had a motor with the exact impeller housing/SST cup issue you said. Salt had built up so much between the housing and the cup that the SST cup was bent inward. I just swapped out the entire housing with another gearcase I had lying around.

I’ll double check that high speed orifice for the motor the customer returned today. That’s just the brass vertical piece in the center of the carb on these models, isn’t it? I’ll figure it out one way or another…it’s usually something simple.

The only oddball thing I can think of beyond what we’ve discussed is that this motor was a 15hp motor that was downgraded to a 9.9 carb. Not sure if this would cause this loss of power at mid and high range (and I’m not talking about just less power, I mean it’s not hitting the RPM’s it should even for a 9.9 configuration).

[fleetwin]

The high speed jet simply screws out of the bottom of the carb’s main nozzle, no special tools needed! Be very careful cleaning it, no drills or other sharp tools, solvent only. I found some very small pipe cleaners the other day at AC Moore (arts/crafts store) which are great for cleaning even the finest coating of varnish from these jets.

[Author]

Posts