Low speed needle settings

[nyer]

I have a 96 or 97 Evinrude 50 horse 3 cylinder. It runs kind of rough from idle up to about 2000 RPM's. The motor shakes. It runs great at wide open. I checked the low speed screws and they are all set at 2 1/2 turns out. Is that close? I need to order a manual and carb kits, I have never rebuilt them in the 9 years I have owned it. It has always run like it does, I thought it was normal. I was hoping maybe the screws were messed with by the previous owner and maybe it's a simple adjustment to fix it.

 

[Daviet]

Re: Low speed needle settings

I think the static setting is about 11/4 turns out and then fine tune with the engine in gear while tied to the dock. Have you tried turning them in 1/8 turn at a time, make sure you give the engine time to adjust for changes.

 

[nyer]

Re: Low speed needle settings

The only thing I did with them is pull them and clean them off. I didn't want to mess with them if they were at the factory setting. I have no problem playing with car carbs but the boat carbs on an outboard intimidate me a little. Do you know what affect having the screws turned out would have on perfermance?

 

[Daviet]

Re: Low speed needle settings

The same as on a car, the further out the screw is turned, the richer the mixture. A rich fuel mixture will cause bad idleing and foul the plugs if run for long periods of time at low speeds.

 

[Monte1961]

Re: Low speed needle settings

Turning them out will cause it to richen up at idle. If at all possible, Find a inductive timing light that has a rpm meter on it. Usually digital, Adjust low idle screws to get the maximum lowest idle possible working between mixture and idle screw. After you find that, turn idle screw to recommended rpm in gear! Just another way.

 

[nyer]

Re: Low speed needle settings

What RPM range do the low speed screws affect? When I hit a certain RPM, around 2500, the motor runs great with no shaking.

 

[Daviet]

Re: Low speed needle settings

You carb has different circuts, low, intermediate and high.
The low speed jets control the low speed circut, when you reach a certain RPM the high speed circut takes over.
So to ansewer your question, it is possiable for one circut to be defective and not affect the other.
It can go both ways, you can have an engine that will not run at high speed but idle perfectly.

 

[nyer]

Re: Low speed needle settings

Ok, just like a snowmobile carb. I will try adjusting the screws in and see if it makes a difference. I have never fouled a plug on this thing even after hours of trolling at idle. I'm sure the carbs could use a rebuild, I do have a little oil seeping out of the bottom one.