I recently pulled my throttle bodies to fix a stuck front idle air needle screw and ended up rebuilding
the throttle bodies. If your bike has more than 50K miles I highly recommend this service as your shaft seals are almost certainly starting to leak and a rebuild/resync will breathe new life into the engine
. Here are four mods that I did to my throttle bodies while I had them out.
Mod1: Front TB Idle Needle Extension:
As anyone who has done the idle air throttle body sync procedure knows, accessing that front needle is a pain in the butt. After my TB rebuild and a plan to replace my rear valve seals soon, I figured I'd need to do a couple of syncs in the next 1000 miles as things settle in. To make my life easier I bought a 24 inch "Z50 MONKEY BIKE SPEEDOMETER CABLE" off of ebay for $12 shipped and modified it to connect to the front needle and make it easier to adjust the front idle air needle. Here is a photo of the end of the cable that mates with the needle screw.
The picture is a bit blurry but I cut off a key crimped on to the end of the cable that would mate with the speedometer. Using my dremel tool, I ground the remaining crimp piece into a slot bit to mate with the slot in the needle and added that spring. That plastic gray piece was rev 1.0 which was later replaced with a simple washer in my final version. Here is how I eventually mounted the speedo cable to the front idle air inlet to hold the speedo-bit against the needle.
I shrink wrapped the metal end of the speedo cable and put a dollop of dielectric grease between the cable and the idle air hose to minimize abrasive wear. The cable routes over the top of the radiator shroud, loops in front of the radiator and I made a bracket out of romex to hold the end of the speedo cable away from the hot parts just below the radiator and to the right of the front cylinder.
The opposite end of the cable has a square key that mates with the speedo gear. To adjust the front needle I used a small crimp/locking hemostat and used its orientation to balance the throttle bodies at idle. After adjustment I wedged the key with a splinter of wood to keep it from moving and then added the rubber cap to keep water out. The hemostat worked fine for the adjustment process but the cable is a bit springy so it takes a bit of feel when doing the sync. I am looking for a removable knob with a set screw for the next time I do an adjustment as I think that would work better than a hemostat for a more accurate sync.
Mod2: Symmetric IAP Vacuum Hoses:
While I had my throttle bodies off I replaced all the vacuum hoses with fresh 5/32" windshield washer tubing. Normally the IAP sensors are tapped to only one of the vacuum ports in the throttle bodies and the remaining port is capped but available for the TB air needle sync procedure (many riders add an extension hose to the side of the bike to make doing the sync easier). I had a different plan for measuring the pressure during the TB sync and decided to use both taps to drive the IAP sensors. Here's how it looked from the engine side of the TBs;
This should give the ECU a better measure of the intake air pressures in each TB and I like the symmetry of it. The bike runs great with this mod but I have no idea if this has any effect whatsoever. Once the TBs are installed the hoses are an indistiguishable black blob so be sure to double check that you get the correct TB plugged into the appropriate IAP sensors mounted on the back of the airbox.
Mod3: IAP Sensor Output Extensions
My bike was having minor driveability and idle issues and had a stuck front idle air needle so before I pulled the TBs I tested all the sensors per the service manual to rule out a bad sensor as a cause. They all passed but the service manual procedure includes steps using a needle probe to test the output of various sensors. I don't have a manometer (vacuum gauge) and I didn't want to mess with one of those home-made ones with tubing filled with oil. It occurred to me that the bike already has pressure sensors built-in so why not use the IAP sensors to do the TB sync instead of separate taps and vacuum gauges. To achieve this goal I added semi-permanent (i.e. easily removed) needle probe wire extenstions of the IAP output leads. I made two needle probes with 16 gauge wire (should have used 18 gauge) by soldering and shrink wrapping a needle made from a small paper clip.
The wires were long enough to run from each sensor and back to the battery area where I was able to measure the differential voltage using my digital voltmeter. Here is the installation of the probe on the right/IAP#1 connector probing the green output wire (red and black power the sensor) which I gooped up with dielectric grease, fed down the shroud and across the engine on the wiring harness to pick up its mate on the other side and then back to the battery area.
I marked the right/IAP#1 sensor with red tape and the IAP#2/left sensor with black tape. For now I have left the extensions longer and just roll them up and tuck them into the left quarter panel out of the way. Eventually I will probabley shorten the wires and crimp on some connectors but I wanted to leave my options open as to where the probes will reside.
When doing a TB sync you need to know which one is which in order to know which needle to adjust to get the TB in sync. The sensors output 4.5v to ~1v with the lower voltage indicating higher vacuum or a stronger pulling cylinder. In my case, I put the red/positive lead of my voltmeter on the IAP#1 and the black/negative lead on IAP#2. With this setup when the volts were positive this implied that IAP#1 has at higher voltage than IAP#2 and thus the front cyclinder was running weaker than the rear cylinder. To correct that I needed to increase idle air (i.e. turn out) on the front cylinder needle and decrease (i.e. turn in) the rear cylinder needle. The logic is reversed if the differential voltage went negative. I did a sync and measured the differential voltage which theoretically should be 0.00 volts if the TBs are balanced. Of course there is a lot of oscillation and noise at idle so the best I could do was sync to +/- 0.25 volts with the signal swinging back and forth across 0.00 volt target. Later after the TB sync, I measured the sensor outputs independently and watch it as the voltages fluxuated and found that the TB#1 sensor fluxuated from 2.52 to 2.59 volts and the TB#2 fluxuated from 2.53 to 2.60 volts. The fluxuations are pretty stable at idle and the TBs are a tiny bit out of sync. The next time I do the sync I am going to add inductor/capacitor to the circuit to damp the oscillations and get a better read on the outputs.
Mod4: 40.4mm Throat Diameters
This one is really an artifact of my rebuild and can't be done unless you do the full TB service. If you read that thread I mentioned that I replaced the OEM screws with shorter ones with smaller, flatter heads. The smaller screws block less flow area than the larger OEM screws so it is equivalent to a small increase in the throttle body throat diameters.
So there you go, four throttle body mods. As always, do this at your own risk, YMMV and the benefits may only exist in my mind.