1974 40hp Evinrude 40455s engine not reaching WOT

[racerone]

Have you checked the reed valves.------One may be broken or held open by debris.

 

[pn]

ditto on the fuel pump diaphram, hold it up to light.

 

[buddhapi]

thank you for the replies. the Yamaha dealer did mention to the last owner about the reed valves, so that was the first thing I checked last fall. they were all good. it is funny you mention the fuel pump. it's not running out of fuel. the primer ball stays firm with the motor running or not. I ran a 9.8 Merc, 90hp Merc and a 150hp Merc on this fuel tank already this summer, so I know the hose and tank are good. what dynamics would a fuel pump diaphram change if the carburetor bowl is being kept full? I do appreciate the help guys.

 

[Otte]

Do you have any adjustable jets on the carbs? I struggled with many of your same issues on my outboard. Turned out to be many different problems on my 1989 50hp that caused rough running, but the last thing to get idle up was a 1.5 turn of a screw on an idle adjustment jet. Just a thought from a shade tree hack mechanic.

 

[fireman57]

It sounds like you are running on one cylinder. Take a timing light and test when running or get a spark gap tester. It should jump 7/16ths of an inch and the spark has to be bright blue not orange. I suspect a bad coil. You are not burning fuel in one cylinder and that is causing your excessive fuel issue. If you want get a new coil and replace one of them, run it and if it makes no difference then swap it with the other one. I'm betting this solves your problem. Also, do not use ngk plugs only champion. These engines were built around champion plugs.

 

[racerone]

Brand of sparkplug does not have that much bearing on how a motor runs !--Just too many " old tall tales " about this.

 

[Otte]

Do you have any adjustable jets on the carbs? I struggled with many of your same issues on my outboard. Turned out to be many different problems on my 1989 50hp that caused rough running, but the last thing to get idle up was a 1.5 turn of a screw on an idle adjustment jet. Just a thought from a shade tree hack mechanic.

 

[buddhapi]

thanks guys. the only adjustment is the idle screw, and I have that set good at the nicest idle spot. I will check my spark one more time, but it seemed to jump far enough and have a nice blue color. I haven't had time to play with it for a few days since the demo derby transmission customers come first, but I do plan on taking it out again Saturday for a calm fishing day. I will update then.

 

[buddhapi]

figured I'd update tonight. I played with it in a barrel today, and it seems to be running better. no more fuel spitting out of the two tiny hoses. I checked the pump diaphram since it was mentioned.I hooked a vacuum pump and rubber nipple to back of pump and pumped up to 15 vacuum and it held. no leak down. I never realized that the pump was vacuum operated off the top cylinder! I assumed it just ran off manifold vacuum through the carb, like an old snowmobile. thanks Racerone and PN. if the wind dies down, I'll test run on the lake tomorrow. hopefully it stays burning clean...spark plugs look sweet!!

 

[Otte]

How did she go?

 

[buddhapi]

Sorry guy's, but I still haven't had a chance to run it again. my old fishing buddy found out he had acute leukemia mid June and passed away last evening. doctors couldn't figure out what was wrong until it was too late. his immune system has been getting weaker the last couple years, but there were no signs in the blood work. he turned 75 on July 1st. best friend one could ever have. I will post more on the boat motor if I get out this weekend.

 

[buddhapi]

I finally got this 40hp Evinrude on the water, on this 15 foot Pipestone fiberglass runabout. I'm about 240 and my hired help is about 180. that, plus the boat must weigh a good 800 pounds. we were able to get the boat on plane and I'd guess about 20-25 mph. motor sounded healthy at 3600 RPM. what I can figure guys.....the excess unburned fuel trapped in those tiny hoses was flooding and bogging the motor down. a few weeks back, I ran it with those tiny hoses disconnected and gas was shooting out of them. reconnected and now I'm happy. rebuilt lower unit, strong top end. now she's ready

 

[UConnMRB]

I cant offer any advice on the motor as that is way above my pay grade, but I am so sorry for your loss.

 

[Otte]

Sorry to hear about your buddy. Glad to hear about the joy the running engine must bring you.