Evinrude 40 Big Twin power loss

BookMan

Cadet
Joined
Jan 31, 2003
Messages
6
Hello All,<br /><br />This is my first boat and I'm not very technically-minded anyway, but here goes ...<br /><br />I am still trying to identify the year of this motor, but I think it's 1970 (model number 40052A).<br /><br />After a few minutes' running on three-quarters power, engine starts to die as if running out of fuel. Easing back on the throttle brings the engine back to life.<br /><br />So it's possible to run on about half-power, but no more. I checked that both cylinders are firing and the plugs both look the same colour so I assume they are.<br /><br />I imagine that this is a fuel problem and have checked all the lines and connectors up to the carb, plus I've cleaned and blown out both the filters.<br /><br />This only leaves the carb which looks a bit tricky to get off as the starter motor is in the way. Before I wade in there (and do some damage), I have a spare carb which I've been looking at. It has the number 379486 stamped on the side, and the number 307777 stamped on the bottom of the float bowl.<br /><br />Inside the float bowl, there is a small needle with a rubber tip which is pushed up as the float rises, stopping the fuel flow. As the level drops in the bowl, the needle is released and allows fuel to enter again.<br /><br />If this needle is sticking, might it be possible that this is causing the problem? As the power is increased, the float drops but the needle does not (or not as much) and so the engine is starved of fuel.<br /><br />So the question is, (a) does this sound likely, and (b) what is the best way to get at the carb (or get the float bowl off at least)?<br /><br />If anybody has any ideas, I'd be very grateful. If I can identify the motor, I see that I can get a manual through this site, which I really should do, but until I can afford it (sigh) any help would be greatly appreciated.<br /><br />Mal
 

BookMan

Cadet
Joined
Jan 31, 2003
Messages
6
Re: Evinrude 40 Big Twin power loss

Hi alcan,<br /><br />Wow - thanks for your really quick response!<br /><br />It looks like I'll have to get in there and take things to bits.<br /><br />Um, about the primer pump - there is a bulb to squeeze to refill the system, but no knob (I think). Is this important?<br /><br />Thanks again,<br /><br />Mal
 

alcan

Commander
Joined
Dec 14, 2001
Messages
2,505
Re: Evinrude 40 Big Twin power loss

Sorry Bookman, must have been some type of snafu. That response was for another post. I'll think about your problem for a minute and get back. In the mean time you think about going to the libaray for a free book (manual). You really can't afford not to have one.
 

Bear

Lieutenant Commander
Joined
Mar 1, 2001
Messages
1,627
Re: Evinrude 40 Big Twin power loss

Alcan's reply is for another question. I read that Q too but now it's gone. Very strange but it happens from time to time. :( :confused: <br />----------------------------------------------<br />BookMan<br />40052 <br />Evinrude 1970 <br />40 hp @ 4500 rpm<br />43.9 cu.in. = 719.4 ccm <br />2 cylinder <br />So you are right about the year, 1970.<br /><br />Before you start tearing it down, try pumping the bulb when it starts to die. If it picks up, get a fuel pump kit.
 

BookMan

Cadet
Joined
Jan 31, 2003
Messages
6
Re: Evinrude 40 Big Twin power loss

Hi Bear,<br /><br />That's a good idea about the squeezing the bulb; it might just force the needle out again.<br /><br />Thanks also for the technical information about the motor. I've copied it into a safe place for future reference.<br /><br />Mal
 

alcan

Commander
Joined
Dec 14, 2001
Messages
2,505
Re: Evinrude 40 Big Twin power loss

Hi Bookman<br /> Float valve sticking could be a cause, also the float level it's self. Do the test Bear suggested. Check to see that the throtle plate is full open. Check the vent on the tank, be sure it's open. As far as removing the carb goes, you may have to remove the starter. I have taken some less expencive wrenches, heated them up and bent them to fit. This helps me save time on some models. I would suggest that on your first time, to take the long way and enjoy the journey.
 

Bear

Lieutenant Commander
Joined
Mar 1, 2001
Messages
1,627
Re: Evinrude 40 Big Twin power loss

Hi BookMan!<br /><br />The squeeze the bulb is more for troubleshooting a faulty fuel pump.<br /> http://marinemechanic.com/2000/images/ob_fuelpump.htm <br />Even if that isn't your problem, it can be a good idea to replace the fuel pump diaphragm anyway.<br /><br />You can try taping the float bowl with a screwdriwer to lose a stuck float valve. But I don't think that is your problem - yet. <br />If this is the problem, get a carb kit and clean the carb.<br /><br />Do you have a library in the neighborhood? Check it out for a manual. Use your $$$ for parts and fuel :)
 

BookMan

Cadet
Joined
Jan 31, 2003
Messages
6
Re: Evinrude 40 Big Twin power loss

Thanks Alcan and Bear for your suggestions, and thanks Bear for the useful link. I have bookmarked it and will browse in detail later.<br /><br />I will go the library today and see if I can find a manual.<br /><br />Unfortunately, the only way to test the motor is to take the boat out. I don't seem to be able to reproduce the problem at home, mainly because running the engine at high revs for an extended time with the water intake in a dustbin full of water is just a little too scary!<br /><br />Thanks again,<br /><br />Mal
 

Lark40

Senior Chief Petty Officer
Joined
Oct 29, 2001
Messages
793
Re: Evinrude 40 Big Twin power loss

If you are going to work on this engine, you need a proper manual. I would suggest the Clymer Evinrude/Johnson 1956-1972 Repair Manual, which is available at all boat stores here in the US, and surely is also available in NZ.
 

BookMan

Cadet
Joined
Jan 31, 2003
Messages
6
Re: Evinrude 40 Big Twin power loss

Hi Lark,<br /><br />Thanks for specifics about the manual. The libraries don't carry it, but I'll see if I can buy a copy.<br /><br />Mal
 

BookMan

Cadet
Joined
Jan 31, 2003
Messages
6
Re: Evinrude 40 Big Twin power loss

Problem solved - it was some damage to the ignition leads, high up under the flywheel where I couldn't see. Apparently it's been arcing out and causing a weak spark.<br /><br />Replaced the faulty leads and now everything is cool. Ran sweetly when I went out yesterday (didn't catch any snapper tho!)<br /><br />Thanks everyone for your input.<br /><br />Mal
 
Top