1995 Force 40 HP - trouble shooting idle issues

I bought a boat which came with a 1995 Force 40hp that had been sitting for several years. I'm going to outline everything I have done up to this point so anyone who can help will know everything I've done.

Repaired/Replaced:

spark plugs
cleaned the carburetor and replaced gaskets
discovered one of the bolt tabs on the carb adapter was broken and had no bolt present. have not repaired/replaced yet.
replaced the water pump impeller
drained/replaced lower unit oil
replaced fuel lines and cleaned the choke solenoid

After all this work I started squeezing the prime bulb and right as it started to firm up gas shot out the over flow port. I proceeded to start the motor, and to my surprise it ran but was shooting gas out the over flow. Figured out the float needle wasn't seating very well. I adjusted the tab on the float and was able to get the needle to seat better. No over flow and motor ran.

On to my problem:

I'm not sure what the ideal RPM is for idle but any RPM under 1000 is rough. The motor will continue to run but it shudders pretty hard.

I ran it for about 1 to 1.5 hours up and down the river and had no issues while running. The idle continued being rough even after the motor had warmed up and had ran for a while. I pulled the plugs and noticed the top cylinder's plug was wet compared to the lower. The lower actually had some sediment on it. I checked compression on both cylinders and both were the same. I can't recall but I want to say it was somewhere between 125 and 130 psi.

I haven't made any adjustments on the carburetor idle mix screw. I have made a couple of adjustments in the shifter linkage to help with some of the slop/tension but none of it has made any impact on the rough idle.

I have a few suspicions as to the problem but wanted to hear other's suggestions before I start part swapping.

Any suggestions?

Thanks in advance.

The broken tab on the carb mount??How about a pic? Pics of the plugs.Could be sucking air at that point?Water in the fuel?
When you cleaned the carb did you reset the air screw?In (gently)till it bottoms out.Then out 1 and 1/4 turns.
Once the motor is warm and in gear,turn the screw back in till the motor buck/coughs/misses,then back out 1/2 turn.
Idle should be 750-800.
Rebuild the fuel pump. Post the pics and try what I suggested.Then post your results.Profile??Jerry

Jerryjerry05 said:

The broken tab on the carb mount??How about a pic? Pics of the plugs.Could be sucking air at that point?Water in the fuel?
When you cleaned the carb did you reset the air screw?In (gently)till it bottoms out.Then out 1 and 1/4 turns.
Once the motor is warm and in gear,turn the screw back in till the motor buck/coughs/misses,then back out 1/2 turn.
Idle should be 750-800.
Rebuild the fuel pump. Post the pics and try what I suggested.Then post your results.Profile??Jerry

Click to expand...

Thanks for taking the time to respond Jerry. Here is a stock photo of what I'm referring to. I have also circled and edited the picture in the area I'm referring to. It's the carburetor adapter.



I located the bolt at the bottom of the cowl so I have used it plus a washer and bolted it back on. Just a temporary repair to see if this helps.

Before I saw your message this morning I rebuilt the fuel pump and reset the fuel/air mix screw last night. When I rebuilt the fuel pump I did not notice any unusual wear or tear. But now it has fresh gaskets and diaphragms so it should be good to go. I did notice that there was a very slow leak from the bottom of the fuel pump.

I also decided to reset the fuel/air mix screw. According to my manual I am supposed to back out 1 full turn from a soft seat. When I turned it in it was approximately 1 and 3/4 turns before it seated. I backed off 1 and 1/4 turn. I'll try and run it on the cups sometime between today and friday and let you know my results.

Thanks again!

Can't set the air screw on muffs.Needs to be in the water and warm and in gear.
Start the motor,spray some starting fluid in the area of the missing bolt.
If it changes anything on the idle.It's sucking air.J

Jerryjerry05 said:

Can't set the air screw on muffs.Needs to be in the water and warm and in gear.
Start the motor,spray some starting fluid in the area of the missing bolt.
If it changes anything on the idle.It's sucking air.J

Click to expand...

Ran the motor on the cups and found I was chasing the idle and air/fuel mixture screw too much. I'll just have to set it to the default setting and adjust it when I go out on the water this weekend.

I was able to bring the idle down to about 800 - 900 and adjust the air/fuel mixture as such and the rough idle stopped. So I think I'm on the right path.

I sprayed both carb cleaner and wd-40 around the carburetor adapter and did not experience any change in the idle so it would seem I do not have a vacuum leak.

Thanks for the suggestions.