Fast Idle Wax Unit & Starter Valve Synchronizing

[Arion]

I had to remove and clean the fast idle wax unit on my bike after a period of modifications with no riding. It had stuck in its bore and would make the engine climb to 4000rpm once warm. The bike only has 7000kms so I don't think its worn out, at least there are no signs of wear. Since the manual warns not to touch the adjuster nut and lock nut on the end of the fast idle unit, I left it alone.

After reinstalling everything, the idle seemed rather lumpy. After warming the engine and clamping off the PAIR hoses, I tried synchronising the starter valves but found that cylinder 1 was drawing by far the highest vacuum, and cylinder 2 the lowest. No matter which way I turned the adjusters, they would move a little but would not equalize. Eventually the adjusters backed all the way out and had to be threaded back in. Cylinders 3 & 4 were some way between 1 & 2, but also would not equalize. Total range between 1 & 2 was about 10cmHg at best adjustment, but the idle had dropped to 850rpm (measured with an external electronic tachometer) and the idle adjuster would not turn further. The engine naturally stalled.

I've removed the airbox a couple of times searching for loose vacuum connections or a forgotten electrical connection but I haven't found any. I have also tried connecting different cylinders to different ports on my vacuum gauge to ensure the gauge itself is working properly. The results are always the same: cylinder 1 very high, cylinder 2 very low, and nothing will equalize without reducing the idle to the point of stalling.

I'm thinking of removing the starter valves completely and blowing out the ports. Is this possible without removing the entire throttle body assembly?

Any other suggestions?

Cheers.

[John451]

Have a read of belows UK VFR Technical Threads on WAX Unit issues, hopefully they may be of some help.

UK VFR Forum Wax Unit Linkys:

http://www.bikersoracle.com/vfr/foru...ad.php?t=58986

http://www.bikersoracle.com/vfr/foru...ad.php?t=64064

http://www.bikersoracle.com/vfr/foru...ad.php?t=87073

[Arion]

Thanks for the links John, although I've checked the things mentioned. I'm pretty sure the problem is not a trapped air bubble near the fast idle wax unit because coolant has drained out of it every time the hoses have been disconnected.

I removed the throttle body and checked all of the vacuum connections on its underside. Everything seems fine. I also removed and cleaned the starter valves for cylinders 2, 3, 4. The problem still persists.

Anyone know of a lubricant that is compatible with the molybdenum coating on the starter valve bores? The Honda manual warns against using solvent cleaners, and many spray lubricants also contain solvents.

Cheers.

[Arion]

Removed the throttle body, checked all vacuum connections, lubricated the starter valves, and replaced the cold start wax unit just in case. Cylinder 1 is still registering by far the highest vacuum, but the lowest is now 8cmHg below instead of 10cmHg. It's a bit of an improvement but still some way off what's required.

I did notice that the small steel shaft on the right end of the wax unit (as installed in the bike) could be depressed slightly with finger pressure. The old unit with 7000km wouldn't budge. Has anyone else noticed this difference between old and new units? The manual just says to visually inspect for damage, but doesn't specify anything more. Visually, the old one looks fine.

When the old unit was installed I noticed it moving the choke shaft to the right, but maybe its travel wasn't quite enough.

[Arion]

Since the starter valves for cylinders 2, 3, 4 (adjustable) were all registering very low vacuum with respect to cylinder 1 (factory set), I reasoned that the problem must be with the starter valves themselves. Cylinders 2, 3, 4 don't appear to have any other single factor in common. Everything was taken apart again and starter valves 2, 3, 4 removed from the throttle body and disassembled.

Everthing was recleaned, the valves and adjuster screw threads were lubricated, and the rubber seals for the adjuster screw shafts sprayed with silicone oil. For reassembly, I decided to apply silicone sealant to the threads of the plastic locknuts on a hunch that vacuum was being lost as air flowed past these locknuts. The manual doesn't mention any requirement for sealing these threads, but it's also curious that there is no rubber seal or gasket between the locknuts and the throttle body. Since the locknuts are plastic, there is also a very real limit on how much they can be torqued.

After reassembling everything and resynchronizing, cylinder 1 was again the highest but I got cylinders 2, 3, 4 to within 3cmHg. It's a big improvement over the initial difference of 10cmHg. As for improving on this even further, I think the only other variable would be to replace the rubber seals on the starter valve adjuster screw shafts. This isn't really an option though as Honda doesn't sell them separately, only as part of a complete $50 assembly for each starter valve, and the seals themselves are not standard o-rings.

There haven't been too many responses to this thread, but I hope the information proves useful, especially to those that have experienced inconsistent fuelling and/or starting problems after major servicing or extended inactivity.