1991 Evinrude 40 HP having trouble at low speed

Motor runs fine at high speed

Motor runs fine at high speeds but at idle or lower speeds seems to cut out or miss a stroke in other words runs rough. Have used Mercury gas additive helps some but still runs rough at low speeds. Replaced plugs today and runs better but still runs rough at low speeds. Have 13 Gal tank. Have though of draining and refill and then use additive. What do you think?

" Bill,

First you should tr

" Bill,

First you should try adjusting the idle mixture. The screw on the starboard side, at the top, toward the rear of the carb is the idle mixture screw. You will notice a spring around the screw which keeps it from moving around.

Start by seating the screw lightly and then backing it out 1 1/2 turns. You might be able to lean it from there a bit to obtain the best idle by adjusting about 1/8 turn at a time and noting the diffference.

If this does not help you probably have to take the carb apart and clean all the components of the idle system.

image{tonyob} "

There is no screw with a spri

There is no screw with a spring around it on this carb. This is a 40 HP Evinrude with oil enjectiom.There are two carb's on this motor. I don't believe adjusting the idling would help because because it runs rough at medium speeds. It backfires or misses ever few strokes. I don't want to have the carbs worked on right now because it is the height of the fishing season right now and it would take several weeks to get the boat back! Can't you thank of anything I could do until I can have the engine worked on? It runs good enough for me to fish but it is a pain to load and unload from the trailer. Thanks for any help you can give me!

"Bill.... OMC made two 40hp mo

"Bill.... OMC made two 40hp models in 1991, a regular outboard and a commerical engine. Both of these engines have carburetors with slow speed adjusting valves located at the top starboard side of the engine as Tony has stated. OMC did however maufacturer a 45hp engine of which the carburetors had all fixed jets with no adjustments. Come back to us with the model number of your engine. The number will be on a plate/tag on the swivel bracket between the transom brackets, and also on a quarter size core plug on the powerhead. From what you've had to say, I'd strongly suspect that the engine has been sitting for awhile which has resulted in fouled carburetors. This makes the engine run lean. If this is indeed the case, the only cure, I'm sorry to say, is to clean those carburetors.

Joe "

" The number on the core plug

" The number on the core plug is G2998776. The boat set up a while during the winter but I hooked it up to a hose a ran it several times during this time. After it wormed up some a couple of months ago, I filled it with AMOCO high test gas and added the mercury additive my dealer said I should use tho help clean the carb. I ran the boat mostly at high speed through about two 13 Gal tanks of gas. I got better and runs good at high speeds but at medium amd low speeds it runs rough ether mixing a stroke or back firing I don't know which. At low speeds like trolling speed in just a minute or two it quits because of this miss firing or whatever is happening. There is a screw on each carb but it does not have a spring but has a brass sleeve around it. this may be the idle screw but I haven't messed with it yet because I didn't want to mess something up. If there is anything I can do to smooth the motor until I can take it to the shop I sure would appreciate your help! "

"The screw with the brass slee

"The screw with the brass sleeve around it is the one that Tony is speaking of. The spring is within the sleeve. Make a note of the exact position of each screw, then with the engine running, back out the top screw somewhat in 1/8 turn segments, waiting for a change of performance between each movement. When the top screw is at its best setting, move to the bottom carb and repeat the adjustment. Hopefully this will give you an improvement. If not, you're most likely faced with cleaning/rebuilding the carb(s).

The number that you quoted is a Serial Number. What is needed to pin point the year is the Model Number. It will no doubt look something like E40xxEIx where the small x's will be various letters, and the EI would stand for 91. There should be a plate/sticker on the center portion of the engine (swivel bracket) just under the lower hood pan.

Joe"

The model number is TE40ELEIA

The model number is TE40ELEIA. I haven't had time to try to adjust the idle speed yet.

I was able to adjust the idle

I was able to adjust the idle speed screws on the motor this morning and it did wonders. Just a slight adjustment it smoothed out the motor a hold lot. It isn't perfect yet but it will idle without quitting and skipping.

Thanks
Bill