can't find idle mixture screw

[swarf99]

hi, I have a 1990 mariner fifty serial no. C258934, the engine smells rich on tickover and hunts as though its on choke, I want to turn down the idle mixture but can't pinpoint the screw, can someone tell me where it is please.

 

[CharlieB]

Re: can't find idle mixture screw

It is unlikely that the idle mixture screws have turned themselves out making the mixture too rich.

Instead, it is far more likely that one or more carbs are flooding, or the fuel pump diaphragm has worn a hole in it allowing raw fuel to dump into a crankcase.

With the motor OFF, adjust the trim level, remove the airbox cover, open the throttle WOT. LOOK down each carb throat while you pump and hold the primer bulb to see if ANY fuel is leaking anywhere. If so, you found your problem.

If not then remove the fuel pump from the motor but leave the fuel hoses connected, again pump and hold the primer bulb while watching the vacuum port of the pump for fuel leaking indicating it is time for a fuel pump rebuild kit.

If both the above check out, check for adequate spark on each spark plug wire, a dead cyl will leave unburned fuel and cause fuel smells.

 

[swarf99]

Re: can't find idle mixture screw

i'm only thinking its the idle mixture screw because someone unscrewed it for me telling me it was in to far, I thought this person knew what they were doing but have now realised that they don't know what they're talking about, I think he said it had to be out 2 turns but i've now read on here how to set it and do it properly and want to do so, i'll check the above while i'm at it but still need to know where the screw is.

 

[oldman570]

Re: can't find idle mixture screw

Idle jet screw should be on the upper right front face of the carb body where the air box is mounted to the carb. A setting of 1 1/2 turns out from lightly seated should get the motor running and it should be adjusted with the motor warmed up and in forward gear in a barrel of water or on the water. Screw the idle screw in 1/8 and let the motor settle out before anymore adjustment is done. Do this till the motor loses RPM or stalls then turn the screw out untill the motor dose the same. The best setting will be half way between when the motor wants to stall in both directions. On motors with more than one carb, I always start my adjustments with the bottom carb first and move up from there. JMO
Oldman570