Annoying Throttle Cam - 15Hp Evinrude '76

[OptsyEagle]

My new motor is working well, but the throttle operation is annoying. When I open it up to higher speeds I have to hold onto the tiller grip tightly or it will back off quickly and the boat will slow down rapidly. I also have a 1975 9.9Hp Evinrude that doesn't do this.

When inspecting the differences, I noticed a big difference in their throttle control cams. My 9.9Hp, shown in the 1st picture below has a nice rounded edge that allows the throttle to open and close at a nice consistent rate. The 15 Hp shown in pictures 2 and 3 has a more inverted curve with a nastly little indent at the end. When at WOT, the throttle roller sits on that indent and then it takes a little force to move it off and at that time the roller rapidly moves down the inverted curve of the cam, rapidly slowing down the motor. Also, if I remove my hand anywhere during this inverted curve, the roller immediately moves to the more rounded area, changing my speed immediately.

Anyone know why OMC would put such an annoying cam on this motor. I am thinking about changing it to the type from my 9.9Hp, but thought I should ask if it will do any harm and also if it should be expected to fit.

The throttle cam on the 15Hp is OMC #320819 and the 9.9Hp is #320434. I was told many times that the only difference between the 9.9Hp and 15Hp of this series (1974-1976) was the carburetor, but I have already found another difference.

 

[Rick.]

Re: Anmoying Throttle Cam - 15Hp Evinrude '76

Re: Anmoying Throttle Cam - 15Hp Evinrude '76

So........... if I take the cam from a 15HP and put it on my 9.9 will I then have a 15 HP.???( provided of course my compression is above 183) LOL Of course I'm kidding but you may have started a new wave of questions.

Mine is an 82 15 HP and I have to hold it pretty hard as well. If I release it she quickly moves toward idle. You have made a good observation there. First time I've heard mention of it. Rick.

 

[OptsyEagle]

Re: Annoying Throttle Cam - 15Hp Evinrude '76

I guess it is because I have had the 9.9Hp with the rounded cam for so long. It is really nice and pleasant to drive. The 15Hp is quite new to me. I am getting use to it, but the throttle is quite annoying compared to the 9.9Hp. I noticed that when I looked up the diagrams for the 1976 9.9Hp they used the 15Hp cam (320819) for H suffix but used the 9.9Hp cam (320434) for R & G suffix models. I imagine the suffix change is just a different model run. They do use a different part number for retainer rings between the '76 9.9Hp and the 15Hp and between suffix changes of the 9.9Hp's. So I am wondering if a different cam would even fit on the retainer ring. Perhaps I can do some measurements.

My other question is "WHY" did OMC use this cam. Maybe they really don't want me to let go of the tiller when it is at WOT. It does have a lot of power and if the boat turned quickly, I can see a person being thrown overboard, but the 9.9Hp has a pretty good surge at WOT as well. The real issue is the force it takes to hold the WOT in that position as compared to my 9.9Hp. Also, when backing off the throttle, I don't see why they would want the throttle to close so quickly with such a little amount of twist grip movement (this is pretty much what this design accomplishes).

If anyone has looked at this issue or has some thoughts on it, I would appreciate it.

 

[OptsyEagle]

Re: Annoying Throttle Cam - 15Hp Evinrude '76

Well I guess no one has come across these different throttle cams so I suppose I may have to play around with them a little and see if I can make it work a little better ... or just get use to the way it is. Thanks anyways.

I do have another theoretical question about synchronizing timing and carburetion. My manuals talks about this and from what I can see they simply want me to make sure that my roller touches my cam at the "arrow" mark. They say that this will adjust the carburetor's throttle opening to the ignition timing. My question is " how does this work". From what I can see, this should synchronize the throttle opening with the markings on the tiller grip and that is about all. I can't see how this processwould effect the ignition timing. Maybe I am reading it wrong or misunderstanding the process completely.

If anyone has some thoughts on this, I would appreciate it.

 

[oldcatamount]

Re: Annoying Throttle Cam - 15Hp Evinrude '76

the idea is to coordinate the ignition advance with the fuel delivery. Those two things have to happen at the same time.

 

[OptsyEagle]

Re: Annoying Throttle Cam - 15Hp Evinrude '76

What does it mean by "ignition advance" and is all this done by ensure the roller hits the cam at the point of the arrow.

 

[AlTn]

Re: Annoying Throttle Cam - 15Hp Evinrude '76

the timing cam is attached to the armature plate which is linked <mechanically> to the throttle handle...as you twist the handle the entire armature plate moves which advances the timing as the carb plate is opened within the carb throat...if you'll look under the fly wheel as you twist the throttle, you'll see this...or if you have the fw off and twist the handle, you'll see it

 

[bktheking]

Re: Annoying Throttle Cam - 15Hp Evinrude '76

The timing cam is actually on the crankshaft, the carb cam is on the plate, 2 different things.

 

[OptsyEagle]

Re: Annoying Throttle Cam - 15Hp Evinrude '76

The timing cam is actually on the crankshaft, the carb cam is on the plate, 2 different things.

I think this is where I get confused. From what I can see it would seem that the ignition timing is determined by the crankshaft cam and perhaps the point gap. So I get confused with this throttle timing.

Are we saying that the point at which the plugs spark (usually close to TDC) will change when the throttle is advanced?

 

[bktheking]

Re: Annoying Throttle Cam - 15Hp Evinrude '76

The point gap is totally about timing (but the gap is static) , as the plate rotates the timing is advanced to compensate for RPM, as the rpm increases so does your fuel/air requirements hence the opening of the carb butterfly, it's all relative. On a car I believe this lack of rotation as the distributer doesn't rotate you have weights and vacuum advance. Once gap is set the timing is "set" so to speak, the only other timing on these motors is the cam relation to the throttle, there is no "timing" setup so to speak.

 

[ChrisAG]

Friction block in throttle grip

Friction block in throttle grip

My new motor is working well, but the throttle operation is annoying. When I open it up to higher speeds I have to hold onto the tiller grip tightly or it will back off quickly and the boat will slow down rapidly. I also have a 1975 9.9Hp Evinrude that doesn't do this.

You shouldn't need to grip the throttle to maintain speed. If the inside of the grip is missing a part called a "Friction block," the speed will decrease rapidly as you describe when you let go of the twist grip.

I know this because when I was a kid I rigged my Johnson 15 with the OMC remote controls for my sea flea, and you were required to remove the friction block for the remote throttle to function smoothly. Once I sold the sea flea (and remote control kit) and put the 15 on an aluminum fishing boat, I was annoyed that the tiller throttle was now so sensitive it required care to maintain a constant speed. Reinstalling the friction block into the handle cured that.

 

[OptsyEagle]

Re: Friction block in throttle grip

Re: Friction block in throttle grip

You shouldn't need to grip the throttle to maintain speed. If the inside of the grip is missing a part called a "Friction block," the speed will decrease rapidly as you describe when you let go of the twist grip.

I know this because when I was a kid I rigged my Johnson 15 with the OMC remote controls for my sea flea, and you were required to remove the friction block for the remote throttle to function smoothly. Once I sold the sea flea (and remote control kit) and put the 15 on an aluminum fishing boat, I was annoyed that the tiller throttle was now so sensitive it required care to maintain a constant speed. Reinstalling the friction block into the handle cured that.

Thanks Chris. Where does this friction block go and what does it look like? This 15Hp did have remote controls at one point in time, so perhaps what you are saying is what I am experiencing. The reason for my follow up question about timing is because I thought perhaps it was the different design of the throttle cams, but certainly did not want to affect my ignition timing by changing the cam.

 

[Daviet]

Re: Annoying Throttle Cam - 15Hp Evinrude '76

Maybe this will help, look at #60.http://www.ishopmarine.com/ishop/jsp/AsplIsmCcatViewBase.jsp?reqFor=29&lvlCode=5&path=BRP%7EA0000003%7EM0004653%7EM0004704%7EM0004705%7EC0074830&isForSupStore=false&cCatFilter=&eCatSupFldr=&hideLinkOnPath=false&docId=&docName=&isFromCMS=false&hideAdd2CartButton=&isStandAlone=&is4CmsShop=&reqln=Unknown&reqem=Unknown&reqph=Unknown&isFrPG=false&forItemCode=&pCode=C0074831

 

[OptsyEagle]

Re: Annoying Throttle Cam - 15Hp Evinrude '76

Thanks Daviet. That's probably it. Do you think that I should be able to get at that part by removing the screw #62 on the twist grip or would I need to remove the entire tiller handle?

 

[Daviet]

Re: Annoying Throttle Cam - 15Hp Evinrude '76

I think you are correct, remove #62 and it should come apart.

 

[ChrisAG]

Friction block & spring

Friction block & spring

Exactly. Ensure you also have the spring.

 

[OptsyEagle]

Re: Annoying Throttle Cam - 15Hp Evinrude '76

That's great. Thanks a lot guys. I hate to be a winer but it was really annoying. Even when you just wanted to slow down a little, the throttle will spring back on you so quick, bringing the boat into a quick decelerating lunge into the water and then you twist it back a little and you can take off like a gazelle and back again. Over time you can kind of get use to it and make it work better but it reminded me of the 1st few minutes learning how to drive a car with stick-shift transmission. The only difference I could say about the outboard was that at least it didn't stall on you like the car did.

Thanks again.

 

[Rick.]

Re: Annoying Throttle Cam - 15Hp Evinrude '76

So was your friction block missing then? I know mine is in place as is the spring. Rick.

 

[ChrisAG]

Friction block & spring in throttle grip

Friction block & spring in throttle grip

Rick, are you SURE your friction block is in place? Along with the spring, it creates a lot of tension with the twist grip, so it shouldn't move at all when you let go.

 

[jmendoza]

Re: Annoying Throttle Cam - 15Hp Evinrude '76

You have the cam for the remote throttle control, change it to the one that is like the earlier 1975.

About timing: The points gap sets the dwell, or time the points stay open. As you open the throttle, it moves the magneto plate and advances the ignition timing. At some point it touched the throttle arm on the carb and opens it until it is wide open, and after that it continues to advance the ignition timing a little more, even though the carb is still wide open.

The purpose or advancing and retarding the timing with throttle is because if you did not, the engine would have to have the timing fixed, and this would have to be a compromise of not too much ignition advance in degrees before top dead center(BTDC) so it would not kick back when starting, or at trolling speeds. But then it would not rev out and have as much top end. If you had full advance, it would be a bear to start, and possibly backfire at low speed, shearing the flywheel key, and or stalling when you suddenly closed the throttle. Therefore, the ignition advances and retards with throttle settings so the engine has smooth idle and trolling, easy starting, and good top end power.