91 Force 40 runs rough

[jcb11257]

Force 40 pulled reeds they look great, rebuilt carb, New Plugs, Compression 125 on both cylinders. Runs out at 5000 but acts like a intermittent
View attachment VID_20201013_131436603.mp4
miss. when idle it shakes and spits like a burnt valve in a four stroke. getting exhaust in cowling. I am at a loss ?? been working on this for a long time. Please help.

 

[jerryjerry05]

Missing at idle usually means the low speed air screw needs adjusting or
it's sucking air somewhere???
Do the starter fluid test: spray sf around the intake side of the motor, base of the carbs and under the coils and packs and around the fuel pump.
If this makes any difference?? then it's got an air leak.
Where's the low speed air screw set at?

Exhaust in the cowl, the gasket at the spacer plate or the mid section is bad.

 

[jcb11257]

Missing at idle usually means the low speed air screw needs adjusting or
it's sucking air somewhere???
Do the starter fluid test: spray sf around the intake side of the motor, base of the carbs and under the coils and packs and around the fuel pump.
If this makes any difference?? then it's got an air leak.
Where's the low speed air screw set at?

Exhaust in the cowl, the gasket at the spacer plate or the mid section is bad.

Low speed air screw ?? all I have is a mixture screw. I ran it in till it seated and backed it out 1 1/4 turn it was a little rich so I turned it in 1/4 turn. Spraying starter fluid around the reeds and carb base was Ok, around the coil packs slowed the engine down almost causing it to die. Im guessing I will have to pull the power head to replace exhaust gasket

 

[jerryjerry05]

They didn't make a 40hp in 91??
They were made in 92 Then 95-99
If it made a difference when sprayed under the pack/coils?? Then the port cover gaskets are probably bad.
One little cough, backfire or stutter can blow the gasket
I'd pull the covers and check the gaskets.
I doubt you need to pull the block
The mix screw is the low speed screw.
Not for rpm's. It makes the operation at low speed smooth out.

 

[jerryjerry05]

A few pics can tell what year your motor is?
You have the sticker on the transom clamp?