Intermittent Full Throttle-'73 65hp Johnson

[little mfg]

Thanks for the info, Bosun!

 

[little mfg]

Hey Jimmbo, good question about the boat cover. In some mysterious way, yes.

 

[jimmbo]

If it runs better with the cowl/cover off, it could be that the Air Inlets are restricted, or you have an Exhaust Leak and that Exhaust Gas Recirculation is causing a Power Drop.
You say the Fuel Economy is poor, even for a boat. Well. a restricted Air Inlet is like a choke

 

[racerone]

Pistons were known to break pieces off the skirt.----Any cracks / holes visible on the outside of the crankcase ?

 

[Tim Frank]

Is this motor new to you?....i.e. has it ever run well for you?

Did you remove the high speed orifices and ensure that they are clean....and corrct ones for that motor?

 

[little mfg]

Hi folks. Thanks again for all the input! Before I got this boat, it sat in a garage for about 10 years. I was told it ran before storage. The previous owner at least had the sense of running the gas out before letting it sit. Externally, it looks great--no cracks or anything on the crankcase. It almost appears that no-one did maintenance on it because the fasteners are for the most part untouched.

Most currently,

• When I pulled the bottom carb, I was not able to pull the high-speed orifice for lack of the proper screwdriver. However, I could clearly see the hole was unrestricted. I cleaned every orifice with carb cleaner and blew out with air. I have to assume the high speed orifices are the correct type since the boat was sold in and never left this general area. I do not like that there is no clip on the original fuel needle to keep it from hanging up when the float drops. This appears to be the OEM design, looking at the manual.

• ---

  The flooded fuel in the carb throats was milky. Could this be simply from aspiration or is it a sign of water entering?

• ---

  The flooding caused sticky goo enough on the electric choke to make it stick. I did not have the silencer cover mounted so that I could work on it while on the lake.

---

• As far as gaskets go, is there any other way of checking them short of pulling the motor apart?

Next, I will try the drop test. Can I do this with the hose hooked up or should I take it on the lake? My burning question is what would cause these brief moments of power/success if the problem were bad gaskets/water intake? I personally have to wonder if I'm having fuel delivery issues, but the upper two carbs seem to be operating normally.

Thanks again for all your input!

 

[Bosunsmate]

milky fuel sounds like water in your fuel source, take off a hose to a carb and pump some fuel into a jar and have a look
many faults on a boat motor are intermittent
you can do a drop test at home

 

[little mfg]

Great advice. I'll be doing that in a bit along with the drop test and will report back. Thanks

 

[little mfg]

I didn't have time to pull fuel from a carb because it started raining. I did get the drop test done though. Cylinders 1 and 2 changed when the wires were pulled. Number 3 cylinder showed little or no change. Uh Oh. If you recall, spark is good, compression is good. Cloudy fuel in flooded carb throats--not verified yet. Any ideas on what I'm in for next? As always, thanks.

 

[little mfg]

Also, please remember that the boat was in dry storage for 10 years. Thanks

 

[Tim Frank]

Hi Tim, Thanks for your help! I have healthy spark on all three, although I have not checked air gap. I do not have a tester to check air gap at the moment, plus the plugs for it don't have the standard electrode because they're the anti-fouling type. I will scrounge an old standard plug and do that! I haven't checked the compression yet, only because it runs so smoothly and doesn't foul the plugs putting through the long no-wake zone to the lake. Maybe a poor assumption on my part. I will do that, too! Thanks for the suggestions.

OK....so if you do not have testers, the answer to MY question is :
"No. I have not checked spark or compression."

The answer to your question:....

Any ideas on what I'm in for next? As always, thanks.

.....is, check spark and compression.....properly.

 

[little mfg]

I bought a spark gap tester and tested all three at 7/16". They all looked healthy to me. I also checked the compression dry. 125, 130, 125 on 1,2,3 respectively. Inspecting the spark plugs was a bit troubling. 1 and 2 were fouled, which for my no-wake river traveling to and from the lake seems normal, BUT the bottom plug was not fouled at all. I'm puzzled!

Hi Tim, I posted this a couple down from the one you referenced. Thanks!

 

[F_R]

I don't know if this is what's wrong with your motor or not.. But here's a history lesson for whatever it is worth. Those motors have a terrible habit of getting water into the cylinders. OMC had to replace a bunch of powerheads under warranty because of it. My father-in-law went through three of them before he gave up and put a Yamaha on the transom.

It is a design problem. The inner exhaust cover plate is poorly (not) supported in the area surrounding the exhaust ports. At even a slight hint of overheating, the plate warps and the gasket leaks, squirting water into the exhaust port. The result is total destruction of the powerhead if allowed to continue.

Now is this what's going on with yours? I don't know. But #3 plug certainly looks like it is washed clean. Also #2 but not as bad.

I advise you to check for signs of water on the plugs after a very brief run before it warms up. I'm not going to tell you how I test for it because it is dangerous.

Good luck and hopefully this is an incorrect guess.

 

[little mfg]

Hey F_R, at this point I have to agree with you. I found this in my manual last night. I didn't know water could wash a plug clean:

Water Leakage in Cylinder

The fastest and easiest way to check for waterleakage in a cylinder is to check the spark plugs.Water will clean a spark plug. If one of the plugson a multi-cylinder engine is clean and the othersis dirty, there is most likely a water leak in the cylinder with the clean plug.

To remove all doubt, install a dirty plug in all cylinders. Run the engine in a test tank or on theboat in water for 5-10 minutes. Shut the engine off and remove the plugs. If one plug is clean and the other(s) dirty (or if all plugs are clean) ,a water leak in the cylinder(s) is the problem.

So, good eye F_R and I see as a retired pro mechanic you ought to know! I have to laugh. I went from working on an Eska to this. Thought it would be a step up, ha ha! You're pic is worth a thousand words. So off come the exhaust plates. I'll post a new thread when I have it back together and tested.

Thanks a bunch for your help. I really appreciate it!!