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So, I have searched google and forums as well and am still not fully grasping it. Maybe a noob question, but what all goes into setting up a decent DCOE side draft setup? If anyone here has done it, what did you do for ignition timing and the afm? Any info will be appreciated. Thanks!
almost too much work for nothing.
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OK here's what's up with that AFM. I got most of this info from Norm Garrett's book. It's a good source of Miata info straight from one of the engineers.
There is a supply voltage of 5 volts to the AFM. The output to the ECU is 5 volts at idle and it drops to 1.5 volts at WOT. It's basically a potentiometer connected to the air flap inside the thing that does this voltage drop.
The ECU sees this voltage and adjust the maps for ignition advance and injector pulse width. The speed of the motor also factors in so if you go WOT and watch the timing with a light, it travels to full advance on a curve. I would assume that the injector pulse width does a similar calculated curve.
So, if you connect the linkage of the throttle to a potentiometer and wire it up to the AFM harness, you can duplicate the action of the AFM as the throttle moves the potentiometer through it's sweep. Right now I have adapted an 86 BMW TPS to the carbs. It works pretty good but the advance curve is pretty agressive. I may wire in a trim pot and mount it on the dashboard! Nice cheap way to be able to change timing on the fly.
There's a fuel pump switch in the AFM that needs to be bypassed by connecting the two wires together. This causes the fuel pump to run whenever the key is in the run position, enging running or not!! The intake air temp sensor needs to be connected because it's output also gets factored in by the ECU. You can use a sensor from another AFM. Just take the cover off, remove the circut board and pull out the sensor. Connect the two wires and place it in the air flow near the intake.
I'm hoping that traffic will be a bit mellower today so I can go test & tune. The tourists and Christmas shopper have made the roads slow to near parade speeds
Looks like you have a 1990-93 1.6L B6P motor car, which is good, because I don't think you'll have as much luck on a '94+ BP motor car without aftermarket ignition system or standalone, at which point you're more than 1/2 way towards ITBs which are much better than carbs under almost all circumstances.
To start, you'll need an intake manifold adapter, good carbs (OER, Weber, Mikuni, Keihin, etc.), a plethora of jets and needles and emulsion tubes and accelerator pumps and gaskets and whatever else is needed to tune whichever carbs you choose. You'll also need to adapt the stock throttle cable or make a new one. You'll need to trick the AFM like horribleR said so the stock ECU will do an okay job of managing spark or you'll need an aftermarket ignition system like MSD. You'll also need a test pipe because you will absolutely destroy your catalytic converter in the process. Optional things that are nice to have are secondary air injection to help with idle droop, a cockpit choke lever, lambda sensor and output gauge. I would also recommend a Halon fire extinguisher and a lot of patience. It can be a fun project so long as you don't have lofty expectations. SCCA EP racers used to run carbs, but the rules changed and so has the level of preparation.
Additional reading
40mm Mikuni CV carbs on a 1.6
Weber Sidedraft Kit-Complete!
You can source manifolds from Harada Shokai or OER in Japan or Jenvey in UK. It would be very rare for you to find a used BOIG or Pierce intake manifold.
About what I was thinking. In all reality ITBs would be a better set up and much easier. I just like the old school factor of carbs. It may happen, it may not. We'll see.
good luck!
My carb conversion is going very slow...but it'll be fun when finished.
Ya, I'm torn between doing a DCOE setup and just going with the Jenvey ITBs. Either way it'll be cool.