Evinrude 25 hp rev out

[pikelucius]

This is not really a problem as much as it is confusing to me. For as long as I remember our 1981 Evinrude 25 hp will rev out with the choke pulled. It seems backwards to me. Its not my motor, and I have never had the carb off. Is the "choke" a priming circuit, rather than an actual butterfly choke? There are no vacuum leaks, and its not running terribly lean. It will do it first start, or fully warmed up. It will rev over 5k rpm even with the throttle fully closed, but I have no idea how long it will go for. Probably until it blows up. My dad says its always done it since he bought it in the the early 90's. He just opens the choke the moment it fires, and its been running strong. Its just now starting to wear out, and he estimates it has well over 1000 hours on it. I may rebuild the top end as a fathers day present next year, so If there is anything abnormal with the carb, I would like to know.

 

[jasper60103]

It has a butterfly choke. I have the same motor and starts the way you described. If it's running good, just leave it be and enjoy.

Edit: Electric start can added fairly easy if it doesn't have it and would make the old man happy for sure.

 

[F_R]

Pulling the choke knob closes the choke butterfly, plus at the same time kicks the throttle butterfly open somewhat. That all is normal. But 5000 RPM seems awfully much. You might want to check the interlock that limits spark advance in neutral gear to see that it isn't going beyond the correct start position.

 

[pikelucius]

I'll think about adding a starter. He isn't that old yet, and it pulls easy. Maybe another year. The reason I want to rebuild is its just plain worn out. It starts easy, and runs fine, but it's getting down in compression, and has had some piston slap for a few years. It's definitely not rod knock.

He has talked about wanting a little more power, so I might have it bored out a little. He could use a new prop as well.

Anyway, yes it will rev very high with just the choke. Since it seems typical, I won't worry about it. Thanks for the replies.

 

[oldboat1]

In the way of a wet blanket post -- I don't think what you describe is normal. Before rebuilding your Dad's motor, I would clean and rebuild the carb, then do the link and sync. It's a 50:1 ratio for the mix.

Sounds like the motor doesn't owe anybody anything, but think it probably still has some life left before a full rebuild. Should idle in the lake in gear at about 750 rpms -- high idle would be maybe 1000 rpms. Use of choke for cold starting is standard, maybe half choke while warm up -- maybe adjusting carb needle 1/8 or 1/4 turn richer for starting, then resetting. But routinely 5000 rpms with a cold engine? That can't be good.

also think your intuition about choke operation is right -- when warmed up, choking the engine should cause it to stumble and probably stall, not rev up. Need to fix that.

 

[pikelucius]

Well it probably just needs a top end rebuild (I'll make sure the bottom end is solid first). I haven't personally compression tested the motor, but have been told its getting low by my dad who owns it. If that's 100 psi, or 125 I don't know. What I do know is the motor now has a lot of piston slap, and that is a good reason to rebuild it. Even if we could milk it out a few more years, its not worth the risk. This motor has given decades of absolutely trouble free service. If only I could say that about my own 84 Johnson 40 hp. I'm doing good if I get a month without trouble with it.

I just looked at the evinrude today, and one thing I noticed is when you pull the choke, there is a rod that slightly opens the throttle as well. The timing seemed to move freely. I'm sure I could just make it richer on the low end until it doesn't do it, but that isn't the proper way to do it.