912UL CV carbs without airbox-what is the fix for the lean running ?

I've also wondered how effective the spraying of wd-40 would be with the prop blast. Being a liquid, likely it would still stay there long enough to get sucked in.  

I would expect that throttle shaft seal to be more of a problem at idle, where the vacuum is greatest.  Of course you did say that had your idle mixtures opened a little farther than the standard 1.5 turns, so maybe you are pulling some extra air in and compensating for it with fuel at idle.  At high cruise, I'd be surprised if it made much difference even if there was a small leak. 

Those seals are kind of a pain to change, so I wonder how often it gets done.  I'm changing them on the 30 year old carbs I've got apart downstairs, but honestly even those looked like they probably weren't leaking. 

Rusty

You are right. They are float bowl vent lines and should not change anything for the slide.  Thanks. Anyway I thought it made a difference but I am doubting that too now. 

I guess I'm getting old. LOL 

What are you spraying WD40 on or in and for what?

Trond Reinertsen wrote:

You are right. They are float bowl vent lines and should not change anything for the slide.  Thanks. Anyway I thought it made a difference but I am doubting that too now. 

The air pressure on the top of the fuel helps push it into the carburetor. If the pressure above the bowl is lower than the pressure at the intake, the engine will run leaner. What I did by putting the vent lines into the air cleaners was to eliminate the varying pressure they were exposed to with the random airflow inside the cowl.

This device controls the air pressure at the vent lines. With it you can richen and lean the carburetors.

https://www.greenskyadventures.com/mixture-controls.html#:~:text=The%20HACman%20is%20a%20device,all%20of%20the%20aluminum%20parts.

Roger Lee wrote:

I guess I'm getting old. LOL 

What are you spraying WD40 on or in and for what?

Bing support suggested to spray WD40 on carburettor and inlet manifolds to look for vacuum/air leaks. Hard to do behind a prop but effective elsewhere. If engine reacts to what you spray on then you have found a leak.