Logo
FULL SITE MENU

Idle adjustments

fastjeff

fastjeff

Gold Medal Contributor
1986 Mercruiser 305 with a Q-Jet. Trying to adjust the idle mixture. I see a tiny hex ?? where the idle screw should be. Is that the idle mixture screw, or a plug with a non-adjustable 'hole' behind it? (And, if it actually is the adjusting screw, what size is the little bugger?)

Thanks,

Jeff

PS: Boat steers fairly well with the power steering pump temporarily disabled (due to a leaking hose).
 
fastjeff said:
1986 Mercruiser 305 with a Q-Jet. Trying to adjust the idle mixture. I see a tiny hex ?? where the idle screw should be. Is that the idle mixture screw, or a plug with a non-adjustable 'hole' behind it? (And, if it actually is the adjusting screw, what size is the little bugger?)
Click to expand...

That would be your low speed fuel/air mixture adjustment screws!
If it is a Marine Q-jet, both sides will be adjustable.

Keep in mind that any adjustment to these will not affect High Speed fuel metering..... only low speed.
 
the idle mixture screws should be "double d". The Tool in the link may help but use a different vendor.

finally, don't be surprised if you can use the flex adapter.....too much stuff in front of the carb on a boat....most of the time the adapter on the end can be used by itself.
 
I have the tool shown and it has all the needed extensions for almost every carb I have needed to adjust.

Works very well on boats that I have used it on, 4, 6, and 8 cylinders.
 
In a pinch, you can push a short length of automotive vacuum tubing ( Approximately 1/8" ) over the screws. The hose will fit tightly enough over the idle screws to allow you to turn the tubing with your fingers to make the adjustment. The tubing can be cut to any length and bent to any angle to allow you to make an adjustment while avoiding the fan belt or other moving parts.
 
Back
Top