Project Miata Update

Made some more progress over the weekend.

– All new clutch hydraulic system filled and bled
– Throttle cable shortened
– Vacuum manifold installed on fuse box bracket where windshield washer bottle used to be
– Vacuum line for MAP sensor routed through firewall to ECU
– Vacuum caps and constant tension spring clamps fit to the hose barbs above each intake runner on the ITBs
– Flexible fuel hoses made

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^^ Picture shows the splayed cable ends after soldering. It is the splayed ends that give the cable end strength. The solder just keeps the ends frozen in that splayed arrangement. I ground the cable end smooth after this shot. I also resused the OEM plastic barrel end bushing and the rubber cable wiper/seal. It’s important to remember to install those items on your cable in the correct orientation before you solder the new cable end fitting on.

I discovered that it wasn’t a good idea to keep the OEM threaded fitting on the end of the throttle cable. Doing so means adjusting the throttle cable requires removing the ITBs, unbolting the threaded block from the linkage plate and turning it one complete revolution and bolting it back on the linkage plate. So next time I work on the car I will cut the cable end off, carefully remove the OEM threaded adjuster that’s been swaged onto the cable conduit, fit a ferrule to the end of the cable conduit and solder a new barrel end on. This will allow me to use a standard hex head threaded adjuster, either the one that TWM/Borla supplied with the kit or a slightly longer one that I have from Flanders.

I also discovered that my aftermarket OMP accelerator pedal cover was too low on the OEM pedal and it was actually limiting my accelerator pedal travel. All these years I’ve only been getting 85% throttle opening! So I removed the pedal cover and will reposition it higher and the right distance from the brake pedal for optimal heel-toe downshifting.

I messed around with the accelerator pedal adjuster and the throttle cable tension to ensure I can easily get WOT without having to bury my foot through the floorboard. I played with the throttle cable routing (clipped into firewall vs. not) to see if there was too much friction between the cable and conduit due to the number of bends. However, the stock setup did just fine with the cable routed this way. I think the double throttle return springs are just way too stiff for this application. Maybe the springs work okay with the TWM/Borla recommended throttle cable routing (straight out the firewall in a big loop around the front of the engine and then 180° back towards the firewall on the intake side) but in my application it’s not good. So I plan to remove them, measure their free length and spring rate, and get something a little bit lighter. Double springs in parallel, of course, for safety and redundancy in case one breaks.

I’m not really sure where to set the idle stop screw on the ITBs for a decent idle since I’m not using ICV at the moment. On my motorcycle carbs I used a piece of piano wire to ensure the each slide lift was the same distance but it’s different with butterfly valves. Will have to wait until I can start the car and see what happens.

The Aeroquip Startlite fuel lines went together easily but I marred some of the fittings because I only had a pair of size 6 AN wrenches that only fit the portion of the fitting that threads onto the fuel rail and fuel pressure regulator return. I was trying to save money by not buying the complete set of AN wrenches. That was a mistake. I also thought I had bought some swivel 45° fittings but they were all non-swivel. In my experience, it’s best for one end of the fuel hose to have a swivel end and the other end to be a non-swivel end. This way you get good fuel hose routing and positioning without having to resort to P-clamps. So I’ll be buying some more AN wrenches and some new fittings to replace the ones that got messed up.

As for capping the vacuum hose barbs above each intake runner, I think they’re only used when TWM/Borla balance the throttle linkage at the factory. The internally balanced vacuum supply with the large hose barb on intake runner #1 should be sufficient to supply all my vacuum needs. It will be routed to my Golden Eagle vacuum manifold. From there vacuum will go to the brake booster and the MAP sensor.

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