Just a quick update on where I'm at with the idle. We left of with establishing the root cause of the engines inability to idle nicely being the charge robbing that occurs via the idle air pipe that joins both throttle bodies. Once this was plugged the air fuel ratio normalised between each cylinder and the engine just sounded a whole lot happier. No more fouled plugs and with the entire IAC system removed no odd idle behaviour hot or cold.
The only downside was in order to set the hot idle to around the factory specified 1250rpm the cold idle needed to be around 800rpm. However with the AFR now sorted the bike is perfectly happy to start and idle at this speed! No need to hang onto the throttle while the engine warms up. But I wanted to see if it was possible to solve the problem and have the ECU control the idle speed. So I got a local engineering shop to make this...
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The idea was to block the tube and force the idle air to each cylinder to travel down individual tubes and reduce the possibility of charge stealing.
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This is the plug that blocks the original IAC tube and feeds each throttle body with its own air supply.
Long story short it didn't work! The air lines are to restrictive to provide enough air to be able to alter the RPM by the required 300 or so needed to account for the engine going from cold to hot. Also it was proving difficult without sealant to block the balance tube so I was still seeing some charge robbing. So I had a couple of choices, spend more money on modifying the design to flow better and using a flexible sealant to glue the plug in. Or I could have machined new independent idle air lines into each throttle body and permanently sealed the old one. But as I only have one to experiment on, I decided not to!
The engine has never sounded better at idle so I'm going to leave it there as I've already spent more than I should! But if you want a fully reversible fix for the idle on your bike, then just get rid of the entire IAC system, block the tube and set the throttle position screw to achieve the desired idle speed. The result is quite spectacular, the engine is more than happy to idle at speeds it could only dream of before!
Rock solid start and idle from cold at 800RPM! Fully warm it sits at 1,200. I give it a couple of blips at the minute mark to see if it will recover back to idle without stalling (which it does).
So I'm going to leave it there, hoping that Norton/Jenvey will make a change to the design of the throttle body in the future (they are both aware of my findings).
. I have actually been thinking of tidying up the oil supply line by lengthening it so it runs behind the frame rail, then over the top of the sprocket cover to the banjo fitting. I guess that would hold a few more cc’s of oil.
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