Is it possible? Pre-VTEC throttle bodies on a 2006

I am interested in switching to a pre-VTEC throttle body assembly to ditch the wax idle unit. Is it possible to run the older throttle bodies on a VTEC bike? I have looked at pictures of them on eBay and don't know that I could make sense of the vacuum lines.

 

The vacuum lines are only different because the 5G has the 4 starter valves mounted to the right side of the TBs, whereas the 6G has the SV integral to each intake. That is why the 5G is missing the bellcrank linkages that run across between the front and rear banks.

Otherwise I believe the vacuum lines are the same, 1 to the MAP sensor, 1 to the fuel pressure regulator and 1 to the flapper solenoid. If I recall correctly, the 5G has a single line to the MAP sensor where the 6G has a 5-way T connecting all intakes to the MAP.

As an alternative have you considered taking the wax unit out of your 6G TBs and adding in a "choke" cable connection to the same point to pull the SVs open manually?

Actually let's step back for a moment. What is wrong with your current wax unit? Seems a common issue is blockage in the small water hoses (so the idle stays high when it should drop as the engine heats), or a seizure of the linkages needing some cleaning and lube. I had a problem with a couple of seized-open starter valves on my 09. And it is also possible for the wax unit itself to seize, as it does behave in a comparable manner to a thermostat.

 

I am finding it difficult to dial in a consistent idle with the bike. Warm-ups are extremely inconsistent. When it is nearly freezing the bike low idles until it's almost warmed up. Shoots into high idle as it reaches 100 degrees (Fahrenheit) and settles shortly after.

Right now the idle adjuster is all the way in and it barely makes the 1400rpm set point. Ultimately, I know there are some underlying issues that need resolved. Short term I intend to replace the thermostat, inspect the cooling system thoroughly as I seem to be losing coolant slowly, and sync the throttle bodies. I've had the wax unit out to clean and even ended up replacing it. If after all this it behaves erratically I will switch to a manual high idle/"choke" lever.

 

Getting the settings right is a bit of an art; I had to "unseize" the reference starter valve and inadvertantly changed the adjustment. Finding the sweet spot where the cold idle was fast (but not too fast) and the high idle settled back by the time the bike reaches around 45C took me about three tries, with changes to synchronisation and readjustment of the idle screw each time, but I got there. I would certainly make sure that your system is in good health:
1. Starter valves are all free to move
2. SV linkage is not getting caught e.g. by a hose, and the pivots are lubricated so the parts move smoothly by hand (easiest to check when the engine is hot and the wax unit is not pulling on the linkage)
3. Starter valves are all clear and flowing air properly
4. The wax unit nut is not constraining the linkage when the bike is hot (there should be some freeplay)
5. All vacuum hoses seal

There is a definite relationship between the position of the reference starter valve, the wax unit nut and the idle adjuster and messing with either the wax unit nut or the reference starter valve will mess that up and may take some time to reset.

Basically the function of the system is:
1. The amount of air flowing through the SVs determines the idle speed. The butterflies seal up tight.
2. The linkage holds all the SVs open to the same extent
3. The 3 x SV adjusters allow the vacuum signal in each intake tract to be matched to the reference SV
4. As the SVs are pulled open further, the vacuum will reduce, and idle speed increases
5. The wax unit pulls the starter valves further open when it is cold to increase the cold start idle speed.
6. As coolant heats, the wax unit slowly lengthens and allows the SVs to progressively close
7. When the engine is above 40-50C, the wax unit should no longer be controlling the SV position, and the SVs are now resting on the idle adjuster screw.
8. The ECU also monitors engine coolant temperature and richens the cold start fuel mixture. I believe this reverts to a normal mixture around 40C.


There's a handy video which I found pretty informative.

 

Thank you for the run down. I picked this bike up abandoned. It needed some serious help. At some point I opted for a new/used throttle body assembly because the reference starter valve black plastic nut was broken. This is the one starter valve for which I couldn't seem to find individual parts. I am inclined to believe the wax unit nut and potentially the starter valves had been messed with on my used throttle body assembly.

I suspect we'll at least have the valves synced. If I can't get the rest to play nice it'll get a manual high idle lever.

 

It is pretty easy to accidentally adjust the reference SV; I was semi-informed and still managed to do it, as the shaft of the SV was seized so there was no spring tension holding the adjuster nut tight and it just came loose in my hand. As long as all your parts are in decent order I don't see any reason why you can't get them all playing nicely. When I started work on my 09, the SV balance was a mile out, the idle was rough making the clutch rattle, and the cold start not very reliable without goosing the throttle. Now it starts on the button, holds 2000rpm cold, and drifts down to 1200 at around 45C, and idles like a watch. May just take a bit of patience. The reference SV adjustment is pretty subtle and a small movement has a substantial effect on the idle. I'd suggest you look up a few SVs for sale on eBay and look at the reference SV position, and compare to your own.