Choke is back on the carb!
Wasn't the easiest thing to put back together, but wasn't insanely hard, either. I'm glad I had 2 other complete carbs to reference though.
It seems Honda hammers down on the back end of the little screws that attach the choke plate to the choke rod, probably to make sure they don't back out and fall down the carb throat. Removing them wasn't easy, and tore up the threads pretty badly. Fortunately I had a tap and a die that were the right sizes (M3x0.5, my very smallest ones) to clean up the threads on the screws and in the choke rod. They're now locked down with blue threadlock instead.
Here's the back of the choke controller. The notched piece in the lower left is the fast idle cam. When the choke is closed, it acts as a throttle stop, keeping it open more than usual. As the choke opens, the cam moves, pulling different notches against the throttle stop, which slowly lowers the idle until it's disengaged and resting against the main idle control stop. On an emissions car, the black plastic fast idle diaphragm slowly pulls on the cam to lower the idle as the car warms up automatically, but on a devacced car, the diaphragm is disconnected. The cam still works, but you need to tap the throttle to get it to change. Since the fast idle diaphragm was useless now, I removed it.
In the picture above, just behind the fast idle cam, you can see the arm that the fast idle diaphragm arm normally connects to. It's supposed to be rotated about 90 degrees, but without the diaphragm arm in place it hangs loosely and interferes with the cam.
Here's the offending piece:
The arm also acts as a spacer for the rest of the linkage, so I couldn't just remove it. A few seconds with a dremel fixed it though:
Of course there's really no reason that you need to remove the diaphragm in the first place, in fact I'm starting to wish I hadn't because I have an idea to get it working even with a devac (more on that later). Good thing I've got spares!
Here's the choke and the controller reinstalled, minus the fast idle diaphragm. I actually originally removed the diapgragm to rebuild it, but one of the screws wouldn't budge and snapped off. I drilled it out and retapped the hole, but I was a tiny bit off center and the new hole didn't quite line up. Some slotting of the black plastic housing made it sort of work, but I wasn't happy with it. Once again I'm glad I've got spares.
When I reconnected the bimetallic coil to the choke, I aligned it so the choke's a bit open at 'fully closed'. I figured since I only needed to cover the chokeless carb with my hand about halfway to get it to start, a completely closed choke at startup wasn't necessary:
When I tested it, it worked pretty much as intended except that the choke opened way too quickly... It was fully open within about 60 seconds... Not nearly enough time for the carb to warm up. To stick with this method, I'll need to put a resistor inline with the bimetallic coil, to drop the current that reaches it in order to open it more slowly. I've got one other idea as well...
I've been trying to figure out a way to put the 'automatic' back into the fast idle controller, the black plastic part normally controlled by vacuum that yanks the fast idle cam out when the car reaches temperature. I thought about connecting the bimetallic spring right to the arm that the diaphragm normally controls (the piece I cut out), which would have meant that as soon as the choke opens, the idle would drop mechanically (similar to the secondary mod). The coil is too weak for that though. While it can adjust the position of the fast idle cam when it's not pressed against the throttle, it's not strong enough to move it under the weight of the throttle spring (which is why you need to tap the throttle to drop the idle on a devacced car... once you lift the weight of the throttle stop off of the fast idle cam, the bimetallic spring can act).
What could work though is to connect the fast idle controller 'drop idle' port to a vacuum source... through one of the thermovalves on the intake manifold. Once the car reaches the right temperature, the thermovalve would open, applying vacuum to the fast idle port, which drops the idle without having to tap the gas. Pretty much the way it was designed to work, but without the complication of the whole emissions system. No fiddling with different value resistors, either. This would eliminate the coil instead of the fast idle diaphragm. The tricky part would be figuring out which thermovalve opens at what temperature, and which temperature is optimal for the carb.
That's where I'm at so far!
While I was taking pictures I took a shot of my 'massive' one-car garage in its current state for good measure. It's getting cramped down there!!!
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