61 evinrude 40 runs very rich with hood on

verno

Seaman Apprentice
Joined
Sep 4, 2003
Messages
41
When I have the hood off it runs great, Idles great, good acceleration, steady under load, in test tank. high and low speed carb adjustments very responsive. When I put the hood on it it starts loading up at idle, and gets really rich at higher speeds. I can get it to lean out with the hood on and adjusting the high speed mixture but only if the screw is nearly shut. Then when I pull the hood back off it goes to extreme lean condition and dies. I have to quickly open high and low speed screws a bunch to keep it going. Put the hood back on and it gets really rich again, not just a little bit but close to flooding. It has great and steady spark. I have cleaned the carb, twice, inspected the air intake port in the bottom cowl and it is not obstructed or nothing mis-aligned, I compared the air intake to other known good running engines I have of the same design.

What might be the problem? I suspect I am missing something simple but have no clue what it might be.
 
Last edited:

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
Re: 61 evinrude 40 runs very rich with hood on

Normally when this happens its the base gasket, its at the bottom of the power head, if it leaks exhaust it gets drawn back into the motor and causes it to run poorly with the cowl on, and normal when its taken off.
 

samo_ott

Vice Admiral
Joined
Jun 18, 2006
Messages
5,125
Re: 61 evinrude 40 runs very rich with hood on

I was going to say air intake but if it's ok then it's usually an exhaust leak. Check the exhaust housing gasket or the base gasket as mentioned.
 

F_R

Supreme Mariner
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Jul 7, 2006
Messages
28,226
Re: 61 evinrude 40 runs very rich with hood on

The answer is obvious. You are running it in a tank. They suck smoke from the tank if you try to run it with the hood on. Get that thing on a boat, on the lake, and see how it does.

Now, if it smothers when running where it is designed to run (on a boat), there are a couple of possibilities.

1. If it smothers at idle or tied to the dock, but is ok under way, it could be the rubber donut between the outer shell and the midsection housing inside. If that is the problem, it should run ok under way because the smoke is buried in the wake, far behind the boat.

2. Otherwise, if it smothers on a boat at any speed, most likely is the o-ring is missing off the top of the water pump housing. OR--if it is a long shaft model there are two more o-rings on the extension tube around the drive shaft. Or, the extension tube itself might be missing. Any of those conditions will blow smoke up under the hood, big time.
 

verno

Seaman Apprentice
Joined
Sep 4, 2003
Messages
41
Re: 61 evinrude 40 runs very rich with hood on

I ran it in the test tank again this morning, (I'm in Oregon) and pulled the hood off when it loaded up. Sure enough there was a shroud of smoke under the hood.

Thanks for the suggestions. Now I go back and start digging. It's been worked on quite a bit and the last thing the previous owner did was convert it to longshaft.

Oh boy, more adventures in old outboard tinkering. Yahoo!
 
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