89 125 Idle Issue

[OldNBold51]

this issue has plagued me for years now and I just learned to live with it.

Problem: at 800 rpm idle in gear, the motor will chug along nicely and out of nowhere backfire/cough and die. I'm guessing the backfire is out exhaust as it's muffled and not that loud. Engine immediately starts up and runs and will do this again just about every time at this idle speed and mostly at the worst time when your needing to reverse/brake coming into the dock.

Jetting: I've got a small tach and I adjusted jetting to gain max rpm's at idle. This setting is leaner than factory spec's.

Timing: I've set timing based on the WOT static method.

Compression: all 4 cylinders are even and high (140 psi).

Any suggestions? This is annoying, especially when docking.

 

[moparman]

Re: 89 125 Idle Issue

usually a lean mixture at idle on a FORCE is a melted piston on the top end .These motors just don't run great at idle ,they are set up for higher rpm and do have a tendency to foul plugs with a lot of idling around. Overall these are super motors and are very reliable with the proper service,but just don't like to idle a bunch. If you have it to where it idles good ,it's usually[that being the key word here] too lean at the upper rpm's and it will burn the piston some what, at least this has been my experience with them. Better to carry some spare plugs and run it rich at idle,just my opinion.

 

[john from md]

Re: 89 125 Idle Issue

The Force carbs idle circuit is used in midrange and WOT. You cannot have this engine run perfect at idle and not have problems at top end. The fact that it is backfiring through the carbs (you can't hear it because of the intake and cowl) tells me it is too lean a mixture.

This can come from mixture screws in too far or from float levels adjusted too low. In any case, you shouldn't make the idle mixture screw setting less than 1 turn out. I recommend 11/4 turns out to be on the safe side.

When you set up your idle, the boat must be tied to the dock and in forward gear. The idle speed setting needs to be set at 700 to 750 rpm, then adjust the mixture and then adjust the idle speed again.

Try it and see what happens.

John

 

[foodfisher]

Re: 89 125 Idle Issue

Coughing/backfiring will damage the fuelpump diaphram.