Originally Posted by
1967brutus
Like the others have stated, it is NOT possible (at least not without great effort) to modify an existing Walbro carb for use with the solenoid.
What you need, is an equivalent to your current carb Stihl M-tronic carb, or one at least compatible to your engine.
Since Stihl uses a different bolt pattern from Walbro, you will need to do some modding here and there.
But once fitted, indeed the electronics as discussed in this thread and the RCGroups thread, should be fully able to do the job for an engine in airplane configuration.
Mind you, you still need a TX with good curve programming functions, and you still need to determine those curves yourself.
It's been a while since I've done anymore work on the wt walbro, been side tracked with a couple projects.
[In reply to the bold]
It's definitely not easy to modify the wt to accept the solenoid valve. I've screwed up two carb bodies in the process of figuring out where all the fuel passages are.
I have one bored out to the correct depth to fit the solinoid, and the fuel passages at the bottom of where the hi/lo needle seats are, once you bore down to the seat tappers, the fuel passages that feed the main jet, and idle / intermediate jets are large enough for the solenoid to modulate fuel delivery correctly, just like the m-carb does.
The issue is plugging the original fuel passages under the welch plug in the metering chamber that feed both needles, and then drilling a new passage from the welch chamber to feed the solenoid valve chamber. Once that is done the carb will operate just as the m-carbs do.
The other thing I would like to achieve, is to relocate the hi/lo needles to the side of the carb body to intersect the main and idle/ intermediate fuel passages to fine/trim the fuel delivery from the solenoid as needed (if needed?). After ruining one carb body, I know where those passages are, so relocating the needles is not as difficult as milling the solenoid chamber and relocating the fuel feed passages.
It's not easy to do for sure, and you need an endmill, or a decent drill press and a solid means to hold the carb body to the mill table. It's not something anyone can do.
Fitting an original m-carb to the engine would be the way to go, but for me, the m-carb is too big to fit in the location inside the cowl without having to move the engine forward, and that's not something I really want to do. So for now, I'm going to just persist and try to finish modifying the walbro.