1966 Evinrude 40HP Big Twin stalls when throttled

[emerson281]

Evinrude 40HP big Twin Model # 40652B
6 Gallon Attwood gas tank

I got this motor professionally tuned about 2 years ago. I can't find the receipt, so I'm not sure exactly what all was does, but I seem to recall some carburetor work (probably a rebuild) and possibly a fuel pump. Both the carb and the pump look brand new. For what it's worth, they (carb and pump) are spotless...they look extremely clean on the exterior. It ran excellent after that tuneup for about 1-1/2 years, then it started acting up.

Problem: It dies when you give it throttle. It starts fine. It idles O.K (both in and out of gear), but as soon as you give it gas, it stalls...even in neutral. Again: It stalls when giving it gas both in gear and out of gear.

History: On a trip a couple of months ago, the motor started fine, idled really nice, putt-putted nicely out of the marina and accelerated fine. It ran at full throttle for about a mile and then began to slow down (lose power) as if I were backing off the throttle. I checked gas tank fuel lines and fiddled with the gas cap...the relief valve on the gas cap was screwed on tight. I loosened it, pumped the bulb and got underway for a full afternoon of stop an go fishing all up and down the river.

Next trip: I made sure the gas cap relief valve was loose (as it should be). Same thing happened (starts, idles, putt-putts, runs for a short period wide open, then loses power). I pumped the bulb, removed and reinstalled the gas tank fuel lines (at the tank and at the engine). This time, I loosened the whole gas cap (not just the relief valve). I started it back up and all was fine for the rest of the day. In fact...the motor sounded and ran great.

Next trip: Before I went, I bought and installed a new gas cap. Same problem. Went through the bulb pumping, fuel line routine again, making sure the relief valve was open (it was), loosening the gas cap, and soon we were are on our way again for another full day of normal usage. The motor sounded and ran great

Next trip: Bought a new tank. Same thing happened again...except this time I could tell at idle that something was wrong as soon as I drove it off the trailer. I cleared the marina, accelerated...and stalled. Went through the whole bulb pump/fuel line routine and got nowhere with it. I had my brother pump the bulb while I tried to accelerate and it just kept stalling out. I ran home, grabbed the old gas tank, put it back in...no joy there either. Ran to the store, bought a whole new hose/bulb assembly...no joy. Got it back home, hooked the water hose up to it , started it and shot some carb cleaner into the carb...same thing...stalls when giving it gas.

When it stalls out after giving it throttle, it definately doens't sound, smell, or look like it is flooding...it seems the opposite..like it's starving for gas.

I can't afford another couple of hundred in labor for this motor. I'm going to have to take a shot at rebuilding the carb and possibly the fuel pump. I'm a little apprehensive about doing so because I've only installed a carb kit a couple of times before: a lawn mower and a generator. I can't seem to find a definitive answer on which fuel pump goes on this motor and if a rebuild kit is available for that fuel pump. I'm concerned as to whether or not the last tune-up I got for it included a new pump, and whether or not it was the right pump.

Does anyone have anything else that I should check prior to tearing down this carb? Is there some other little trick that somebody knows that can help me diagnose this issue. I really want to make sure that I've covered all my bases before I tear into that carb.

Thanks,

Shane

 

[geoffwga1]

Re: 1966 Evinrude 40HP Big Twin stalls when throttled

Hi Emerson.your problem could be carb related in which case easy to fix,plenty of "How to" on here,on the other hand it could be a coil that is breaking down .It often happens that they will work fine when cool but when they warm up they begin to fail.Also an easy fix but you have to figure out which one first.One way is to run the motor normally until the problem kicks in,then remove each plug lead in turn to see if she's only running on one cylinder.Coils are relatively cheap and available right here on iboats,and pretty easy to install. If it still runs on either we're back to the fuel system.Could be a pinhole in the pump diaphragm.
Good luck.Geoff69a1

 

[emerson281]

Re: 1966 Evinrude 40HP Big Twin stalls when throttled

Hi Emerson.your problem could be carb related in which case easy to fix,plenty of "How to" on here,on the other hand it could be a coil that is breaking down .It often happens that they will work fine when cool but when they warm up they begin to fail.Also an easy fix but you have to figure out which one first.One way is to run the motor normally until the problem kicks in,then remove each plug lead in turn to see if she's only running on one cylinder.Coils are relatively cheap and available right here on iboats,and pretty easy to install. If it still runs on either we're back to the fuel system.Could be a pinhole in the pump diaphragm.
Good luck.Geoff69a1

Thanks for your time...I will check the coils using this method you describe. I will not have to wait till it warms up for the problem to kick in...it now does it right away. I pulled the boat home and let it sit on the driveway for a hour or so before I put the muff on it. It started right up , but it wouldn't take any throttle right away...didn't have to wait till it heated up before the stalling began.

I found the how to on checking the fuel system and I'm gonna go though all that too before I tear this carb down.

 

[F_R]

Re: 1966 Evinrude 40HP Big Twin stalls when throttled

More than likely, the high speed jet (orifice plug) is dirty. Remove the hex head plug from the bottom of the carburetor and look at the end of it. Does it have a coating of gum or varnish on it? If it does, the jet down in the hole probably does too, and that is your problem. A special screwdriver is required to remove the jet. You can also clean it in place by submerging the carburetor bowl in carb cleaner.

 

[gm280]

Re: 1966 Evinrude 40HP Big Twin stalls when throttled

After reading your post, it could very well be what F_R alluded to. Also check your fuel pump as well. Does your fuel bulb go flat or can you squeeze it and change the condition? If you are having this problem in every gear including neutral I'd look at the carb first. Seems your transition from idle to high speed is the problem area in the carb. And that IS the high speed jet or orifice exactly like F_R stated. The fact that you stated that you can’t smell gas points even further to the carb high speed circuit. It sounds like it is bogging for lack of gas and could be a plugged jet/orifice. I’d start there...

 

[emerson281]

Re: 1966 Evinrude 40HP Big Twin stalls when throttled

I got some time today with the motor. Checked the coils and they seem fine...the motor didn't like it much when I removed either plug wire, but it kept running.

As per F_R's suggestion:

Remove the hex head plug from the bottom of the carburetor and look at the end of it.

I removed the Plug Screw and the end of the screw had a thin coat of varnish on it.

Also check your fuel pump as well. Does your fuel bulb go flat or can you squeeze it and change the condition?

No, the bulb does not go flat and squeezing it doesn't help. The fuel pump is not original (at least it looks nothing like the one in the parts catalog that I got in the mail yesterday). I see a number on the fuel pump cap: 329972, but can't track down anymore information about it, so I really don't know what model fuel pump it is or if a rebuild kit is available for it. Any suggestion?...Need a picture?

You can also clean it in place by submerging the carburetor bowl in carb cleaner.

Do you mean that I can remove the Plug Screw, fill a container with carb cleaner and hold the container up to the carburetor's bowl so as to submerge the part of the carb's bowl that has the Plug Screw/Orifice Plug on it (without removing the carburetor)?

A special screwdriver is required to remove the jet.

What kind of screwdriver?...I bet I can get my hands on one. If I "clean it in place" would I need to remove the jet?...or are you saying that I don't need to remove it if I clean it place? Edit: found the screwdriver (how to make one anyway)

Could this potentially be a temporary fix? Should I assume that if the Plug Screw and Orifice Plug are gummed up, other parts in the carb are too? I'm not opposed to rebuilding the carb, if I should, but I will have to ask for a little guidence in terms of the correct kit to buy. I found these here on iBoats: FAQs - iboats. I read a little about the available kits and it seems these kits do not have the float and possibly some other parts? Is the OMC 0439075 kit with the float the correct kit for my '66 and do you guys think it's necessary to go with a kit that has a float?...or should I "clean it in place" and get back on the water.

 

[stephenw]

I had pretty much the exact same thing happen to me as described in the original post. slow power loss while wide open then it started running like garbage. Motor is a 1962 big twin 40 hp.

Compression is right at 110 on both cylinders.

I have cleaned the carb twice (fixed main jet carb). No issues found.

Replaced both coils and condensers for good measure, points looked fine and were still at .020

Fuel pump is good no pin holes.

Runs rough at idle now and needs more throttle than normal then all of a sudden revs up and smooths right out like normal, then all of a sudden starts running rough again requiring a little more throttle to keep it going.

Sent a PM to the OP to see what fixed his issue but no response yet. Scratching my head and looking for suggestions for next steps.

 

[pro-crastinator]

Please - Do not laugh at this post.
Check that spark plugs are tight. (not loose)
Yeah, yeah, it happened to me.......... similar symptoms.

 

[GA_Boater]

I had pretty much the exact same thing happen to me as described in the original post. slow power loss while wide open then it started running like garbage. Motor is a 1962 big twin 40 hp.

Compression is right at 110 on both cylinders.

I have cleaned the carb twice (fixed main jet carb). No issues found.

Replaced both coils and condensers for good measure, points looked fine and were still at .020

Fuel pump is good no pin holes.

Runs rough at idle now and needs more throttle than normal then all of a sudden revs up and smooths right out like normal, then all of a sudden starts running rough again requiring a little more throttle to keep it going.

Sent a PM to the OP to see what fixed his issue but no response yet. Scratching my head and looking for suggestions for next steps.

Start a topic of your own. Don't expect an answer on the PM, emerson hasn't been here in over a year and a half. Read the Help Tip on top of the page.