1992 Mercury 150 Idle problems

[bassinT]

I have a 1992 Mercury Black Max 150. When I crank it up it will idle in neutral as long as I keep it throttled up to about 1500 RPMs. However, when I let off the throttle and it reaches the normal idle speed it will run for about a minute and then it starts to sputter like it’s starving for gas and it will eventually cut off. If I have been running at full throttle and then stop it will idle in neutral for about 3-5 minutes before it starts to sputter and cut off. When it’s idling in gear it does fine as long as it stay’s a little above 1000 RPMs.

My first thought was that my primer bulb was bad and I have replaced it and the gas line. However, it still has the same behavior. I checked the idle speed with the engine in gear as recommended in the Mercury repair manual. It is idling around 750 RPMs as the manual recommends. Does anyone have an idea of what else I could check?

 

[gss036]

Re: 1992 Mercury 150 Idle problems

Rebuild the fuel pump and maybe clean the carbs. You did not say whether it is carbed or efi.

 

[bassinT]

Re: 1992 Mercury 150 Idle problems

Rebuild the fuel pump and maybe clean the carbs. You did not say whether it is carbed or efi.

It's a carbeurated motor. I recently decarbed the motor and ran deep creep through the carbs... but it probably didn't clean the carbs thorougly. I'll try renuilding the fuel pump and see if that helps before I go into the carbs.

Thanks for the reply!

 

[studlymandingo]

Re: 1992 Mercury 150 Idle problems

Is it loading up with fuel? Could be a sticky float. Also, have you checked your spark at idle?

 

[andy6374]

Re: 1992 Mercury 150 Idle problems

If it is sputtering then it is likely running lean. This in general is caused by 3 things, 2 of them already mentioned (dirty carbs and ailing fuel pump). The 3rd is the throttle shutters in the carb throats nut completely shutting when the engine in neutral. Take off the air box, put the engine in nuetral and verify they are fully closed.

The fuel pump is easy to check. Pump the primer bulb at idle and if the saves the engine...it's your fuel pump.

If using the enricher (the 'choke') saves the engine then your carbs are likely dirty. BTW: Deep Creep doesn't clean your carbs!

 

[bassinT]

Re: 1992 Mercury 150 Idle problems

Is it loading up with fuel? Could be a sticky float. Also, have you checked your spark at idle?

It seems to be starving for gas so I don't think it's loading up with fuel. I haven't checked the spark but it seems like it would continuously have a hard time idling if that's what it was. It wil idle fine for several miutes in neutral after I've been running at WOT...Could the spark cause it to behave that way?

 

[bassinT]

Re: 1992 Mercury 150 Idle problems

If it is sputtering then it is likely running lean. This in general is caused by 3 things, 2 of them already mentioned (dirty carbs and ailing fuel pump). The 3rd is the throttle shutters in the carb throats nut completely shutting when the engine in neutral. Take off the air box, put the engine in nuetral and verify they are fully closed.

The fuel pump is easy to check. Pump the primer bulb at idle and if the saves the engine...it's your fuel pump.

If using the enricher (the 'choke') saves the engine then your carbs are likely dirty. BTW: Deep Creep doesn't clean your carbs!

Thanks for the advice on the shutters...I didn't think about checking them more closely. I've had the airbox off and they appear to be shut but I will double check to make sure that they are completely shut at idle. BTW...On the Deep Creep can they claim it will help clean your carbeurateurs, which I'm not so sure about, but it seemed to do a wonderful job of getting the carbon build up out of the cylinders.