1990 Force 120 Lean Misfire

[bigmatt14]

Got a 1990 Force 120 that's running lean and popping. Prior to this, I pulled the carbs, replaced carb gaskets, checked reeds, checked spark, and compression. I basically I did all the preliminary diagnostics before I arrived at this conclusion, with the help of an automotive mechanic friend.

It smooths out and runs great when carb cleaner is fed through the bottom carb. There has to be a leak somewhere behind the carbs causing this lean condition, right?

Anybody have any idea what's going on? Is this a common occurrence with these motors?

Thanks

 

[pnwboat]

Re: 1990 Force 120 Lean Misfire

What about a bad fuel pump diaphragm, or sticking one way check valve in the fuel pump? Sometimes you can squeeze the primer bulb while the engine is running which pumps more gas into the fuel bowls which will "fix" a pump that is not working well.

 

[bigmatt14]

Re: 1990 Force 120 Lean Misfire

Haven't looked into the fuel pump yet. I'll do that tomorrow and post back.

Thanks

 

[jerryjerry05]

Re: 1990 Force 120 Lean Misfire

How did you set the air screw? 1 turn out.You have good gaskets? Try spraying ether around the intake,see if it changes anything.
You check the reeds.How about a compression test.J

 

[roscoe]

Re: 1990 Force 120 Lean Misfire

Perhaps it is just running lean because the idle mixture screw is set too lean; or a small speck of debris is clogging it.

Give the mixture screw 1.5 turns out, then turn it back in 1 turn.

 

[bigmatt14]

Re: 1990 Force 120 Lean Misfire

Perhaps it is just running lean because the idle mixture screw is set too lean; or a small speck of debris is clogging it.

Give the mixture screw 1.5 turns out, then turn it back in 1 turn.

Unfortunately, it isn't the mixture screw. Played around with that three different times with no results. I'm going to check the fuel pump and post back later today.

Thanks guys.

 

[bigmatt14]

Re: 1990 Force 120 Lean Misfire

Fuel pump checked out fine, as did the idle mixture screws. Any other ideas?