How does manual primer system work on 1985 Evinrude 25hp

[stevenvalerie]

I have a 25hp Evinrude (E25RCOS) with a manual primer system. I am very confused as to how it works. I know that when you pull out the handle there is gas squirted into the carb. Atleast I think.... There is a hose that goes to the intake and one that goes to the carb. I assumed that the one going to the intake was to provide vacuum but after a closer look, it is hooked in a tee with the carb hose. So the intake hose gets fuel also.

I began troubleshooting this because my motor was running only on the bottom cylinder. After some trial and error I found that unhooking the intake hose going to the primer makes the motor run perfect. Turns out, there is fuel getting pumped into the top cylinder through this hose and causes a flood condition. I took off the intake and reed plate to inspect. There is a part below the top cylinder's reeds that is a called a valve drain. Its only on the top cylinder. Just a flat small piece of metal with a screw. That metal is rusted and almost completely rotted away. What does this do? I feel like it is responsible for the flooding of the cylinder from the primer system.

As of right now, I have to have the hose hooked up to prime the motor and get it to start, once started, I have to unhook it for it to run on both cylinders.

Any help with understanding how this primer system works would be great. If I could figure out how it works, I would know what I need to replace. I have a feeling that valve drain will need to be replaced, I just don't know what it does.

 

[F_R]

Re: How does manual primer system work on 1985 Evinrude 25hp

As a 2-stroke engine runs at slow idle, it tends to puddle fuel in the crankcase. The drain valve does just that---drains it off.

 

[stevenvalerie]

Re: How does manual primer system work on 1985 Evinrude 25hp

Okay, that seems to make sense. But it raises some questions. Where does it drain to? Why is there only 1? Why would is there only a drain for the top cylinder and not the bottom. Also, valve drain (flat piece of metal) is located directly behind the nipple coming off of the intake that hooks to the primer system. I am not sure if that valve drain is causing issues or if the primer system is messed up. Fuel is getting to that nipple even with the primer closed.

To help everyone understand here is a link to the valve drain part:
OEM Parts

It is part# 9. There is a single screw holding it in place. The metal is very rusted and only about half of it is there.

Also, any help on understanding how the primer system works would be appreciated. I have a feeling gas is not supposed to get to the intake when the primer is closed, but then I dont know if its supposed to go there at all. Why have a line feeding the intake AND the carb?

 

[F_R]

Re: How does manual primer system work on 1985 Evinrude 25hp

I believe #9 drains the bottom cylinder, letting excess fuel out but not in (because of the reed). Bottom cylinder because that is where gravity accumulates a puddle. Older motors drained both cylinders and unceremoniously dumped it overboard. Can't do that anymore.

Beyond that, I confess I'm not all that familiar with that silly primer system. Somebody else can take over on that. My experience centers around older motors, with a good old choke system.