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Inspecting Outboard Motor Reed Valves

In this video I take the reed valves out of the Yamaha 20HP 2-stroke to see if they are damaged and causing a lean running condition.

Inspecting Outboard Motor Reed Valves – Video Transcript

Hey there, Dangar Stu here. Today's video is about reed valves and is proudly sponsored by MarineEngine.com.

This video is likely to be about more than just reed valves because what we're looking at is why we've got this lean sneeze condition on the Yamaha we did the timing on last week. I'll have a look at the reed valves first so we can rule that out as a problem or fix it if it is a problem. And then we'll go from there. Sorry about the background noise the constructions still going on down the \road. What I'll do though, the very first thing I want to do is just fire it up so we can have a listen to it again. I'm going to wheel it in the shop now. We'll take the carburetors and the Reed valves off and we'll take a look. Just gonna start by taking the airbox off to get to the mounting bolts for the carburetors. Reed valves sit between the carburetors and the crankcase and they're essentially just another form of one-way valve. You see a lot of one-way valves with fuel like in a primer bulb, but in this case it's a one-way valve for stopping gas flowing backwards. Once I've got the airbox off I can just take these ten mil fasteners that hold the carburetors on. Once the carburetor is unbolted there's a few things you may need to disconnect. One of them is always going to be a fuel line. Fuel has to get into them somehow.

These ones also have a choke connector and sometimes there's a throttle linkage. Sometimes they're free. They just run on a cam so they're not actually physically connected. It just touches up against it. In this case, the throttle linkage is just a cam so I don't have to do it. There is a fuel line and there is a choke, though. This cover is a little bit wedged in there so I'm just going to take the pull start off to make them easier to get out. Okay there we go. Two carburetors one for each cylinder and then just a front face plate. There's six bolts here that hold this plate on and that's the plate that the reed valves attach to. So six ten mil fasteners and we can just pull that out. There they are. It's nice and easy. It's not a hard job to get these out. Carburetors off, a few bolts and it pops out easy like this.

So we'll take those over to the bench and I'll show you what they're like. So here's what they look like. One for each cylinder or one set for each cylinder. And the valves themselves are these little metal plates like this. If you see here they can open from the inside like this and there's a metal barrier here that stops them over extending and opening too far. So they'll come open until they hit that metal stopper. So air comes in through the carburetor. Then, as it comes in, it opens the valves but the valve can't open the other way. As the air pressure rises here it actually forces them closed. So it only allows air & fuel mixture to come in this way not to escape back out. If these valves aren't working properly, air and fuel can get back out. So if they're broken if you see here they're not sealing. So theoretically when you look through it you shouldn't be able to see any light. So to me that's one of the biggest tests. If I can see light through it, it's not sealing properly.

If they're cracked chipped, bent, anything like that they're not going to seal properly. If you ever see fuel spitting back out of a carburetor, quite often it can be because the reed valves aren't working correctly. I can't see any obvious fault with these. None of them are broken, none of them are bent. You can't see light through them when you're looking inside. So I actually think they're pretty good. I think we give them a clean bill of health. The only thing I will say is the gasket behind here looks a little bit funny. And here's another set off a different outboard, which doesn't have that on it at all. So I'm tempted actually to throw these ones on just to rule one thing out. But, having said that, I think they would still seal and I can't see any real problem with it. If it didn't seal there, you would have what's called a vacuum leak where you're getting fresh air sucked in making the mixture leaner than it should be.

But that's something I'll go over in a separate video again one day. Reed valves are found exclusively on two-stroke motors. You don't have them on four-stroke motors at all. So I'll just quickly show you on the board what they do and how to strip most of the works. I'm not sure if my lame diagram is going to help our hinder, but here's the idea. This is the carburetor here, which is at the front of the outboard. And air comes in. And then this carburetor bowls got hold of fuel. And then the two get mixed up and they come through these reed valves. So the reed valves open and they get sucked in. Now this happens, because as the piston is traveling up it creates this sort of vacuum or a partial vacuum here in the crankcase. And that's what draws this air fuel mixture in into this crankcase. It's sealed in here behind or below the Piston. This is compressing fuel and air mixture from a previous life at the top. The spark plug fires it, then the piston heads back Down. As the piston heads back down there's a port here in the side, the top of the piston and eventually it gets uncovered. At the moment sort of covered by the piston. And as it gets uncovered all this gases under pressure, that has been pushing the piston down, eventually escape out here which is the exhaust port.

As the piston comes down it actually compresses this air fuel mixture that got drawn in in here in the crankcase. If these reed valves are closing properly, it can't compress that mixture here. It's just going to push them back out to the carburetor again. So presuming these are working properly; it compresses this mixture. And eventually the piston gets far enough that this port here opens up. And then this air fuel mixture can come in here and come up to the top of piston and the whole thing sort of happens again. So the whole idea of these reed valves is to allow air fuel in, but to seal off and allow that air & fuel mixture to be compressed by the piston heading back down. So hopefully from that you can see why it's really critical that these work. If they're not working what's going to happen is its going to end up with this lean mixture because the fuels just being spat back out the carburetor. Then, eventually, a very weak mixture is going to come into the piston. The top of the piston. It's going to have some old exhaust gases in there too and nothing's really going to happen. You're going to end up with these sort of symptoms similar to what we've got now. A really common symptom of bad reed valves is a motor that's just really hard to start.

Because these reed valves checked out okay, I'm going to take a look at the carburetors. To be honest with you, one of the most common causes of a motor running lean is blocked carburetors. When people come in with an outboard that's not running well, I would say 80% of the time a carburetor clean solves the problem. Because I've already got another video on cleaning carburetors, I won't bore you with the whole process again. But I will show you what we find with these ones. Just out of interest now you've heard the motor. The only real trick to taking carburetors apart is when you take the mixture screw out just count how many turns you need to wind it all the way in before you take it out. That way you can put it back to the same place. It's probably a little bit hard to see on the camera, but this idle jet is completely blocked. So it's looking like this is just a dirty carburetor problem. Hopefully you can see with that one now you can start to see through it.

That's just a little bit of carburetor cleaner and compressed air. One thing I should mention, while I think about it, relates to last week's video on doing the timing for this outboard. Using the timing light. And I'm surprised no one chipped me about it. But what it was is I adjusted the original linkage and I couldn't get enough travel to get it within spec. So I then sort of adjusted something else and adjusted something else. And that's fine because it gave me the reading I was after and showed you the idea of how to use a timing light. Which was the point of the video. But I don't like to adjust linkages like that to their full travel. What I would like to have done and what I will do with this outboard afterwards, to the final point, is actually adjust that top linkage even further. Which allows me to bring other linkages back into the mid-range. This is good for two things. It means I can fine-tune it later, backwards or forwards, because that linkage that adjustable linkage or stop though isn't at the end of its range and unlike having anything at its limit. It also means that I've got a bit of scope to find that balance between the correct idle timing and the correct total timing at wide open throttle on the water. If you don't have things sort of sitting in the middle of their range you're really limited where you can go. So that's just a bit of a finer point about that timing video I probably should have mentioned the other day.

Carburetors are a clean. They're put back together now. So let's pop them on the motor and start it up. It's now night obviously so it's a bit dark here sorry. I'll put the water on. We'll prime the bowls because we cleaned the carburetors. The bowls will be empty. So we'll prime it up put the water on and see what we see. So as you can see there it's almost 100% not better.

I've got to confess. During this series of videos they've more just sort of been videos I've wanted to do rather than the order I would diagnose this problem. It was definitely leaking from the head gasket and I thought time to do a head gasket video. So I did that. Wanted to do a timing light video. So that needed changing anyway because it was definitely out. So I'm glad that's done. Wanted to do a video on reed valves so now you've seen what they are and what they're about. I've got the point now we're pretty much done all the videos I wanted to do with this motor. So now we'll actually get into just genuinely diagnosing what's wrong with this thing. So we'll check the ignition next week. Maybe this will be a slightly more practical video. I did the video on CDI ignition in the past. I think maybe that's a bit technical and a bit theoretical. So we'll get to the bottom of just testing this one and then see if it's problem see if we get sort it out. Somebody said this outboard was going to turn into the new Evinrude 150 and it looks like their prophecy is coming true. So we'll see it again next week and hopefully I'll see you again next week.