hkeiner
Lieutenant Junior Grade
- Joined
- Oct 17, 2006
- Messages
- 1,055
I have a 1996 Mercury 150hp V6 carbed outboard. It has a thermal air valve on the starboard cylinder head with a hose running from the valve to the carbs. This valve is part of the low idle system. When the engine temp is below 100 F, the valve should be closed in order to restrict air to the idle circuit so that there is a richer fuel mixture when the engine is cold. When the engine warms up, the valve should open to allow more air to the carbs during idle. The Mercury shop manual explains the operation of this valve very well but it does not explain how to test it for proper operation.
Is there a good way to test the proper operation of this valve without removing it from the motor? I am particularly interested in confirming that the valve is properly opening when the engine is warm. I am trying to identify or eliminate this valve as a possible cause of excess smoke when my motor is re-started when warm. I figure that if this valve is stuck closed, then I would be getting too rich of a mixture when the motor is idleing warm and thus causing excess smoke. (note: I plan to also troubleshoot the oil injection system and carbs as possible causes of excess smoke, but want to troubleshoot as many potential culprits as possible. Particularly those that are easy to check out).
My best guesses as to how to test the thermal air valve are as follows:
Plan 1 - Blow air thru valve
1) Start with cold motor.
2) Disconnect existing hose from valve and connect a second short piece of hose in its place.
3) Blow by mouth into the newly connected short hose and confirm that air CANNOT be blown through the valve.
4) Reconnect original hose from carb to the valve.
5) Start motor (on muffs) and warm up engine.
6) Turn off engine
7) Again disconnect existing hose from valve and connect the second short piece of hose in its place.
8 ) Again blown into the newly connected short hose and confirm that air CAN be easily blown through the valve.
9) If results of steps 3) and 8 ) are positive, then valve is working OK.
I am not sure how much air can be blown by mouth through the valve when it is warm and whether one can discern a difference when the motor is cold or warm. If blowing by mouth is not accurate enough, is there a way to test using other equipment, such as a pressure gauge and/or tire pump setup?
Plan 2 - Temporarily disconnect hose from valve
1) Warm up the motor (with muffs) and observe level of smoke at idle.
2) With motor running, disconnect hose from valve and observe any change in level of smoke at idle.
3) With motor running, cover end of hose going to carb with thumb and observe any change in level of smoke at idle.
If there IS a noticable decrease in smoke after the hose is disconnected from the valve (step 2), the valve is NOT opening and is defective. If there is NO noticable difference in smoke when the hose is disconnected (step 2) and there is NO noticable difference in smoke with a thumb covering the end of hose going to carb (step 3), the valve may be OK but the air passage to the carb barrel or idle air bleed jets in the carb may be plugged.
Thanks for any input
Is there a good way to test the proper operation of this valve without removing it from the motor? I am particularly interested in confirming that the valve is properly opening when the engine is warm. I am trying to identify or eliminate this valve as a possible cause of excess smoke when my motor is re-started when warm. I figure that if this valve is stuck closed, then I would be getting too rich of a mixture when the motor is idleing warm and thus causing excess smoke. (note: I plan to also troubleshoot the oil injection system and carbs as possible causes of excess smoke, but want to troubleshoot as many potential culprits as possible. Particularly those that are easy to check out).
My best guesses as to how to test the thermal air valve are as follows:
Plan 1 - Blow air thru valve
1) Start with cold motor.
2) Disconnect existing hose from valve and connect a second short piece of hose in its place.
3) Blow by mouth into the newly connected short hose and confirm that air CANNOT be blown through the valve.
4) Reconnect original hose from carb to the valve.
5) Start motor (on muffs) and warm up engine.
6) Turn off engine
7) Again disconnect existing hose from valve and connect the second short piece of hose in its place.
8 ) Again blown into the newly connected short hose and confirm that air CAN be easily blown through the valve.
9) If results of steps 3) and 8 ) are positive, then valve is working OK.
I am not sure how much air can be blown by mouth through the valve when it is warm and whether one can discern a difference when the motor is cold or warm. If blowing by mouth is not accurate enough, is there a way to test using other equipment, such as a pressure gauge and/or tire pump setup?
Plan 2 - Temporarily disconnect hose from valve
1) Warm up the motor (with muffs) and observe level of smoke at idle.
2) With motor running, disconnect hose from valve and observe any change in level of smoke at idle.
3) With motor running, cover end of hose going to carb with thumb and observe any change in level of smoke at idle.
If there IS a noticable decrease in smoke after the hose is disconnected from the valve (step 2), the valve is NOT opening and is defective. If there is NO noticable difference in smoke when the hose is disconnected (step 2) and there is NO noticable difference in smoke with a thumb covering the end of hose going to carb (step 3), the valve may be OK but the air passage to the carb barrel or idle air bleed jets in the carb may be plugged.
Thanks for any input