Thermal air valve is it needed?

[wow]

hi,
Whilst looking over my outboard yesterday a 1991 mercury 2.5 200hp i noticed the thermal air valve had a broken where the pipe attaches to it. Just wondering if it is needed should i replace it or can i cap off the pipe.

thanks

[wow]

I think its something to do with cold start .

[Techteam]

So if you are refering to a fuel enrichment valve it could lead to a couple of problems. If it the fuel supply pipe to the valve it could drain one of the carbs spilling fuel into the cowl with the risk of fire as well as poor running. If it's the supply pipe to the middle carb that maybe could drag in extra air and lean off extra cylinders with a chance of seizure but it would be fairly remote.

[wow]

hi thanks for reply no its neither of them its a vacume pipe that runs from this valve and its linked to all 3 carbs the valve is screwed in to the top of the starboard side head and has a spring in it like a thermostat

[Techteam]

There should only be 1 pipe connected at the top of the valve the other port is open. All the valve does is restrict air to the idle circuit when the engine is cold allowing a richer mixture. So if the pipe to the carbs has broken off the mixture will be slightly lean at idle which could cause poor idling when the engine is cold. If you blank it off when the engine gets warm it will be slightly rich which if you idle for long periods could lead to fouling. Your call.

[wow]

excellent thanks very much for your help. exactly what i wanted to know.

cheers