1985 force 85 running rich on cylinder 3

[Badeeba]

My Force 85 appears to be running extremely rich on cylinder 3 at low RPM, there is excesive smoke and the smell of unburnt fuel until I get to about half throttle. It also runs really rough at lower speed. Compression is 123-125 all 3 cyl. Fuel pump has been rebuilt with new diaphragm and check valves. Fuel supply holds pressure. Float valves seem to be seating. Did linc and sync. Spark plugs are new. Idle screws are all at 1 turn out. Just did a decarb. It sometimes backfires through carb at start. All of these maintenance items have had no impact. It runs great at WOT. Any ideas?

 

[pnwboat]

Re: 1985 force 85 running rich on cylinder 3

Fuel recirculation check valves would be the first thing I would look at. Item 35, 37, 38 and 44 in the diagram below. Especially the screen #35 gets plugged up.

Mercury, Mercruiser, Force, etc. - POWERHEAD - FORCE 85 H.P.

 

[Badeeba]

Re: 1985 force 85 running rich on cylinder 3

Will I need both of those gaskets 34 and 41?

 

[pnwboat]

Re: 1985 force 85 running rich on cylinder 3

Yes, it would be a good idea to have those just in case.

 

[Badeeba]

Re: 1985 force 85 running rich on cylinder 3

I've got it apart and there is a small dam of debris behind the screens. Can these be removed and cleaned? If so how do I get them out? Also what should the reeds behind it look like if they are problematic?

 

[jerryjerry05]

Re: 1985 force 85 running rich on cylinder 3

Usually the screens need to be replaced or removed completly.The screen is NLA from most parts places.
The newer model motors have the screen too.F429811 you'll need 3 This might fit??
The reeds need to fit flat against the body.They removed them in later models.

 

[tater76]

Re: 1985 force 85 running rich on cylinder 3

Sounds like timing to me. You have covered the bases on the other critical areas. If I set my timing to far advance or retarded it will pop through the carbs. Also, the screw on the front of the carb is not the idle screw, it is the air screw. Idle is set on the timing tower. I will never understand why all the parts breakdown sheets refer to this screw as the idle screw? Anyway, check your timing i bet its out a little.

 

[Badeeba]

Re: 1985 force 85 running rich on cylinder 3

Sounds like timing to me. You have covered the bases on the other critical areas. If I set my timing to far advance or retarded it will pop through the carbs. Also, the screw on the front of the carb is not the idle screw, it is the air screw. Idle is set on the timing tower. I will never understand why all the parts breakdown sheets refer to this screw as the idle screw? Anyway, check your timing i bet its out a little.

Timing is set at 28deg at WOT while cranking.

 

[jerryjerry05]

Re: 1985 force 85 running rich on cylinder 3

The screw is called the idle needle. It's for the low speed air/fuel mix.
Idle screw is on the towershaft like tater said.

 

[Badeeba]

Re: 1985 force 85 running rich on cylinder 3

Here is a video of it running. Notice the rough running and smoke at fast idle. This is after cleaning of the recirc. no change in perfomance. Any other ideas? Carbs? Fuel lines? Vacuum leak? Ignition?

 

[jerryjerry05]

Re: 1985 force 85 running rich on cylinder 3

Won't play.
Plugs burning ok?
Clean carbs. While they are off,check the reed valves.
Bent,broken, missing or open too far?
Excess smoke at idle is a thing all pre-mix motors do.They need to be run and burn up the excess oil.

 

[Badeeba]

Re: 1985 force 85 running rich on cylinder 3

Fixed the video, let me know if this looks normal. Cylinder 3 plug is darker than 1 & 2 also. Smoke smells like unburnt fuel and burns eyes.

 

[foodfisher]

Re: 1985 force 85 running rich on cylinder 3

Looks and sounds about right. Maybe a little rich on the fuel/oil mix. Just one backfire can damage the fuel pump diaphram. Won't hurt to recheck it.

 

[Badeeba]

Re: 1985 force 85 running rich on cylinder 3

Looks and sounds about right. Maybe a little rich on the fuel/oil mix. Just one backfire can damage the fuel pump diaphram. Won't hurt to recheck it.

Running 50:1 Quicksilver oil. I will recheck the diaphragm.

 

[tater76]

Re: 1985 force 85 running rich on cylinder 3

Stupid question, but did you perform a spark check? It will run on two cylinders, and that would explain a rough idle.

 

[Badeeba]

Re: 1985 force 85 running rich on cylinder 3

I have spark on all 3

 

[tater76]

Re: 1985 force 85 running rich on cylinder 3

Just watched the vid, sounds just like my 85hp. Mine also smokes like that after start up, at least for a little while. Is it running rough when in gear idling? or just idling at the dock warming up?

 

[Badeeba]

Re: 1985 force 85 running rich on cylinder 3

It runs rough until about 1/3 throttle

 

[jerryjerry05]

Re: 1985 force 85 running rich on cylinder 3

What are the rpm's at idle? Should be about 1100-1200 800 in gear.
The first 1/3 is operated by the low speed side.Needs to be done in the water. The air screws set at 1 1/8 turn out.Then after it's warm.Turn top screw in 1/8 of a turn.Wait 10 seconds for the motor to use the fuel from the old setting.Then in 1/8 again again wait 10 seconds.Do this untill it cough.stutters or dies.REMEMBER THAT SPOT!!! Then back the screw out (again 1/8th turns)until it rolls or gallops.Then turn the screw back 1/2 way to the other spot.
Do this on all three.
Needs to be done in the water.Motor warmed up.
But before that,clean the carbs,and make sure the jets are clear.Check the reeds while the carbs are off.

 

[Badeeba]

Re: 1985 force 85 running rich on cylinder 3

I have gasket kits coming for the carbs next week. Are you suggesting I adjust the idle mix in gear in the water, or just in the water?