Re: 71 evinrude lark runs great,runs better with hood off
Your motor is a hydro-electric shift model. There are a pair of wires that run from the inside of the lower cowl, on the port side, down into the exhaust housing (midsection). You will see a pair of connectors with rubber boots on them, right next to the point where the wire runs down into the housing.
Exhaust leaks at this point are very common. The wiring section that runs through the housing is encased in rubber and has a bulb just below the adapter plate, which is an aluminum block that is installed between the top of the exhaust housing and the bottom of the powerhead.
To determine if you have an exhaust leak, remove the engine cover, run the motor and watch for "smoke" coming from access port that the wire runs down into. You may also see soot marks in that area.
If you do have a leak, it needs to be stopped, because motors usually don't run well when breathing exhaust gases. To do this, you will have to gain access to the adapter plate, by removing the exhaust housing covers. These covers look like a "ring cowl" and consist of a front and rear piece. They are held in place by four screws that run from inside of the lower cowl, down into the pieces, and by four screws that hold the front and rear sections together.
Once you gain free access to the port in the adapter, you will need to seal the wires. Lack of a seal is usually the result of the bulb in the rubber casing not being pulled up into the adapter plate, but I don't like to pull on the wires to reset it. These wiring sections are no longer available and they sometimes become brittle. For this reason, I prefer to simply seal the port by injecting temperature resistant silicon into the hole, around the wires. I apply the silicon liberally, so that a plug forms around the wires.
Take a look at your motor to see if this might be your problem. If not, let us know and will try to offer further guidance.
