Evinrude Big Twin 40hp issues

[liliysdad]

I just purchased a 15ft Thunderbird with a 40hp Big Twin on it that has been sitting for at least a year, more than likely two. I brought it home, and cleaned the carb, and she fired right up, and seems to be pumping water just fine. The compression is good on both cylinders, and has wonderful spark.<br /><br />Now for the question. I can start the engine on the first crank, and it idles all day long, but when I go to advance the throttle to anything over a fast idle, it falls flat on its face, and tries to die. However, if i leave the engine choked, it will rev all the way to WOT with no problems. Running Lean, right? I screwed with the needle adjustment to no avail, any ideas??<br /><br />Oh yeah------Model Number 40852C<br /> Serial Number E01870

 

[Fouled Plug]

Re: Evinrude Big Twin 40hp issues

Did you remove and disassemble the carb to clean? If so, check the primer bulb on the fuel line to make sure it stays firm under load. Could be a fuel pump or tank venting issue. And replace that impeller!

 

[liliysdad]

Re: Evinrude Big Twin 40hp issues

I was gona replace the impeller, but it pumps hella water, so I called the PO, and he said it had been replaced about a year ago.<br /><br />I didint pull the carb off, ijust ran some B12 through the lines, and filled the bowl up, and then drained it. <br /><br />The Bulb stays firm during operation, and it seems to be getting plenty of fuel to the carb, just unsure of what the carb is doing with it.

 

[rolmops]

Re: Evinrude Big Twin 40hp issues

Hello.<br />If your engine is from between 1960 and 1963 you have a high speed and a low speed adjustment needle valve and you will have to adjust both.<br />Forties from 1964 on have a fixed high speed orifice.<br />Oh never mind ,I saw that you have a '68

 

[rickdb1boat]

Re: Evinrude Big Twin 40hp issues

More than likely your carb is still fouled up. Remove it again, clean and rebuild it using a kit and carb cleaner. Running on a lean condition will destroy the engine.

 

[Lark40]

Re: Evinrude Big Twin 40hp issues

Rolmops,<br /><br />They went to fixed-high-speed jets on the 1960 40hp models.

 

[Joe Reeves]

Re: Evinrude Big Twin 40hp issues

liliysdad..... The carburetor is clogged/fouled, gummed up. Remove the carb, clean, and rebuild it properly. Be sure to clean the brass fixed high speed jet that's located in the center bottom portion of the float chamber. Attempted short cuts are a waste of time. When you're finished with the rebuild, adjust the carb as follows.<br /><br />(Carburetor Adjustment - Single S/S Adjustable Needle Valve)<br /><br />Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.<br /><br />Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running. Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting. <br /><br />When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

 

[liliysdad]

Re: Evinrude Big Twin 40hp issues

Thank you very much. The only reason I have not pulled and rebuilt the carb is that I was still in the "do I want his boat or not" phase, and it all hinged on whether the outboard would run or not. Now that I know it does, I will do a full carb rebuild. Thanks for the info.