Exhaust fumes are starving my '64 5.5 Evinrude.

[Kismet]

We are not amused.

Especially since I just got it back from the local (only--and that's a 50 mile round trip) motor repair shop, which quoted one price on a carb rebuilt and billed me three times that. He did nothing more than his first quote called for, but...what can you do? There's the bill. Pay it.

Took it to the lake and ran it for the first time in more than a month. Sure seemed weak...if that makes sense. Fiddled with connections, hoses, fuel tank...like that. Ran it for an hour or so, dropping a hook here and there. Started and ran, but not happy. Took the cowl off and it was like the motor I remembered! I zipped around (well, zipping for a 5.5 ) for 45 minutes like a kid, waiting to see if anything else was a problem. Put the cowl back on and...anemic power, once again.

But if it were an old motorcycle, I would have said it was being suffocated. Came back, took off the little sponge filter and cleaned it, but that thing is an inch or more from the carb throat, so even if it were solid, the carb would still be able to breath.

Dutifully did my web search and found the carb is probably suffering from carbon monoxide poisoning. One very well detailed site showed four possible causes of exhaust filling the cowl and starving the engine of oxygen.

So, I find myself not trusting the engine guy, not really up to tearing down lower units to see if I can fix it, and currently having more invested in the engine than it is worth on the market.

Eventually, I'll find someone I might trust, but in the meantime, has anyone vented their cowl on a small OMC engine? As reluctant as I am to modify the cowl, perhaps a couple of well-placed, discreet openings might "clear the air."

A small scoop on either side? A ram scoop on top, with a vent hole at the back? Need to keep the attachments in place to make sure the pull rope will still fit through its opening.

Near as I can figure, the CO isn't going to damage the engine, nor poison the driver. I just need to get it vented.

Anyone? Something?


(Or, if I'm way off base, please let me know.)

Thank you.

 

[sixgun86]

We'll if it didn't need to be vented before than it shouldn't need to be now in order to run correctly. Sounds like the high speed jet needs to be adjusted for WOT. Been awhile, but I believe it is turned all the way to the right until closed, then back 1.5 turns left. Then adjust will running at WOT, when you start losing power or bogs back it off. Since yours has been adjusted slightly already you could try minor correction while under throttle.

Someone here might be able to confirm this for me.. You should call your local shop and tell them. What did your bill say? 3hrs for carb rebuild?

 

[Andrew04]

Exhaust shouldn't be any different than before with only a carb rebuild. Mechanic owes you, especially at that price. Have him finish tuning the needle valves.

 

[Kismet]

Exhaust shouldn't be any different than before with only a carb rebuild. Mechanic owes you, especially at that price. Have him finish tuning the needle valves.

Six? This only has a low-speed adjustment knob.

And mechanic will never see me again, unless he's looking up as he crosses the street. :twisted:

Doesn't explain the astonishing difference with cowl off.

I'm almost positive it is an accumulation of carbon monoxide in the cowl, starving the engine for oxygen. From what I browsed, I'm not unique in this.

Thank you, though.

others?

 

[Charger25]

I don't think that a little exhaust will starve the engine as bad as what you're saying. If the exhaust gasket is leaking you should see some smoke around the block when pulling the cover off. What I'm getting at is one of my 25's needs a new exhaust gasket and when the cowl is removed when running there is oil smoke under the cover,but it will still run fairly well for an abused motor. The only time I had to put louvers on a cowling was on a 200 merc when I had to swap power heads.
If all the mechanic did was work on the carb, then maybe he didn't hook up the linkage correctly and the cover is some how keeping you from achieving WOT. Try marking throttle position on the tiller handle at WOT with cover on and then off and see if there is a difference.

 

[bbstacker1]

Why did you have the carb rebuilt, was the engine not running right before that was done? If it wasn't running properly before the rebuild is it doing the same only worse now? We know the engine was designed to run with the cowling on and if it was running properly before the rebuild but not now then you need to look for something that has been changed since the rebuild, such as a missing seal or misaligned linkage.

 

[Kismet]

Carb was rebuilt as part of the engine not running right. Worked fine in the barrel at the shop.
On the water: with cowl in place--anemic; with cowl off, spritely. Cowl is NOT crimping, shorting, touching any engine parts.


Here's one mention of exhaust issue, this one from a Johnson 9:

Exhaust Housing : There is a rubber boot that connects the exhaust housing to the outer middle cowling exhaust water outlet. This boot is notorious for becoming cracked & when this happens, you can again get exhaust gasses inside the engine cowling creating the same problem stated above. One way to test for this situation is to remove the cowling & see if the idling improves. You may still get some contaminated air into the carburetor, but at least you have increased the odds of it getting better clean air. Your best option is to take it the lake or pond, & adjust it on the boat under a load, or if you must adjust it in a barrel, get a fan to blow the exhaust away from the motor and barrel because in a barrel you do not have as much a chance to dissipate any exhaust gas that the engine may be re-breathing.

So, no body else? I guess everyone else would track down and replace the leak. :?


Here's the article on the four possible exhaust leak spots:

There are four known exhaust leak issue with the 9.5hp Johnson/Evinrude series motor from 1964 to 1973.

Here is a digital parts diagram of your motor and for ordering parts.

https://www.marineengine.com/parts/vinta ... 600001.htm


1. Is the exhaust housing seal. (Trash or debris could be lodged under between the rubber seal and the wall of the motor exhaust house cover. With a flashlight you can look under the motor or put the motor on its side and visualize the exhaust housing seal.) Worst case you will have to drop the lower unit to inspect the seal.

*** It could be damaged or miss-shaped over the years.

2. Is the exhaust hose. Could be dried and cracking or torn but not visually seen. With the motor cover off and the motor running, take a bit of soapy water and pour it over the hose to see if bubbling occurs, kind of like checking for a leak on a bike or auto tire.

3. Is the shift rod boot. (bad news is this part is NLA (no longer available)

** Some have tried to repair it using hardening high tempered gasket sealer. (Make sure it is fuel/oil proof and high temp resistant. I have been told they apply the sealant around the boot to seal up the tear or breakdown. *** I have not tried this so I can not attest to its success, but have heard from experience tinkers that this sometimes works. No guarantees....but if that is the source then you don't have much to loose except running the motor without the cover.

4. Impeller housing and drive shaft (washer and seal) The washer and seal together help prevent exhaust gases from ascending above the exhausting boot in the motor cover area. These are parts are often missing or worn, because people don't realized there purpose.

 

[bbstacker1]

Kismet, the 9.5 is a completely different animal and yes is was/is known to have problems sucking in it's own exhaust. Not to say it can't be happening but I would look for something else as your problem. Do you have any kind of insulation in the cowl that is maybe getting sucked over the carb opening, your linkage is opening all the way with the hood on correct?

 

[Charger25]

If you have a barrel, put it in there and start it up.Put a little extra oil in fuel to make good smoke. after its up to temp put it in gear and rev it up some but not too much. You should be able to see where its leaking from. The only other thing is to pull it apart and replace every exhaust gasket there is .

 

[Kismet]

I'll keep looking before I do anything.

I was so happy to have found what I thought was "effect---cause" relationship.