Mercury xr6 -Thermal Relief Valve Questiont

[Iron Horse]

Ok... Before I get bombarded, it’s a carbed ‘92 XR6 I know she is going to smoke. Engine was smoking excessively at idle. Carbs rebuilt, new plugs, plug wires, link and sink, bleed lines inspected for cracks new thermostats and poppet valve. Engine idles about 800 rpm (on the hose) with about a 75 rpm fluctuation either side of 800. I believe she is still smokin too much. Starting hot or cold, all you have to do it look at the key and she fires. The thermal air valve has one line running to the carbs. The other port was capped. When I removed the cap the idle did smooth out but still has slight shutter during rpm fluctuations and smoke did decrease. OK .... the question is should the lower port of the thermal air valve be capped?? I attempted to
post video of the engine idling....that didn’t work. Any help would be appreciated.

[rock]

The air valve opens to atmosphere once engine gets to temp leaning mixture. Should NOT be capped.

Rock

[Iron Horse]

Thanks Rock!!
Do you happen to know if the valve can partially fail and just restrict leaning out the mixture or is it all or nothing? Am considering pulling the valve and cleaning it ultrasonically using Simple Green or Purple Power and water over 100 degrees. Would this be worth the effort?

[tlwjkw]

is oiler deleted?.. make sure tha motor is at least neutral or a tad positive trim when its at idle for any period of time...

[rock]

I know very little about the valve other than it's purpose. Could maybe put it in hot water and blow on hose once it hits temp to see if it is functioning properly but if removing cap help issue my guess is it is working fine. As far as smoke goes, the more the better in my opinion. Means it's lubricating plus it pisses off tree huggers. Win win.

Rock

[j_martin]

Pre-mixed fuel or variable oil system?

[Iron Horse]

VRO removed and fuel is premixed at 50:1. Don’t know the history of the engine so I have been going through it system by system before I cut her loose on the water.

[j_martin]

VRO normally mixes much leaner than that at idle, so some smoke is expected.

[Iron Horse]

I think we can put this thread to bed. I pulled the TRV and it was closed. Put iit in a solution of Purple power and 140 degree water in my ultrasonic cleaner. After 30 min. There was a small amount of debris in the solution and the valve was open. Dried the valve out and let it cool. Reinstalled and ran motor. Valve operated as per on the motor. Bumped the tilt up slightly past neutral. Smoke it at an acceptable. Thanks to all that offered advice. Rock don’t worry as I will still be lubed up and pissing the tree huggers off for you.

On to the ignition system.

Just a side note on what I learned about the valve operation.
The valve uses radiant heat from the cylinder head to open and close. As air is drawn through the valve by the carbs from the atmosphere of the open port it is only heated as it passes through the valve which is a very short travel. The air from the valve does not enter the cylinder head. The bottom of the valve is sealed. For what it is worth; hope it helps.