'98 VFR800FiW to '01 VFR800Fi1 Increase in Fuel Consumption and Loss of Power

[Odie]

The Symptom
For no apparent reason, the fuel consumption increases quite drastically. This can also go alongside a loss of performance. This can have quite a rapid onset, or it can worsen over a periods of time.


A bit of Technical Information
The PAIR system is designed to reduce emissions by allowing fresh air into the exhaust under certain operating conditions to reduce pollution and make sure any unused fuel gets burned in the exhaust. The PAIR system consists of a solenoid valve (controlled by the ECU), 4 reed valves and a bit of pipework.

With the solenoid valve open, fresh air can be drawn from the airbox through the 1/2" diameter rubber pipe connection at the front of the airbox and flow through the reed valves, passages in the cylinder head and so into the exhaust. The reed valves are there to act as non-return valves to prevent the exhaust gases from flowing back up the pipework and into the airbox.

Now if the reed valves don't work (broken, clogged, not seating properly) exhaust gas can flow back into the airbox contaminating the incoming air. This means that there won't be enough oxygen to burn all the fuel in the cylinders and the bike will effectively be running very rich, with the unburned fuel going out of the exhaust valves.

The exhaust gases will also be hot and under some pressure so they will affect the information that the Manifold Air Pressure (MAP) sensor and Air Temperature Sensor in the airbox send back to the FI ECM.

As you may guess by now, the reed valves are exposed to exhaust gases and therefore do get clogged with carbon and other shit. This tends to lift and hold them off their seats slightly and so you get the problems outlined above.


Location of the Reed Valves
The reed valves are located under square covers on the front and rear cam (rocker) covers. The rear set can be easily accessed by raising the fuel tank, the front set are a bit more fiddly. To get at the front set, sufficient access can be gained by going between the front forks, removing the oil cooler's mounting bolts and easing the cooler down slightly.


The Fix
Luckily the fix isn't too difficult. :D

Firstly you'll have to remove the reed valve covers, they're only held onto the cam covers with two bolts. Don't bother removing the rubber hose if it's stuck, the covers can be eased to one side.

Next the reed valves need to be removed from their location in the cam covers. Remember which way up they go, but if you forget all is not lost. You just have to think which way gas is meant to go through them.

Once removed, you can start the cleaning process. Brake Cleaner is pretty good for loosening the carbon build up.

To do a proper job of cleaning them, the reed valves need to be dismantled further. They're held together with a single small nut and bolt. Make sure you use a good fitting screwdriver on the bolt as it's not the toughest metal ever made.

Once dismantled, you can clean all the individual parts up. Brake Cleaner, Solvol Autosol and Scotchbite do a good job of it. :D If you do need to scrape the carbon off with something more aggressive, be careful not to score the reed or it's seat on the plate, otherwise it won't seal.

Once clean, the reed valves can be reassembled and refitted. I'd recommend using some thread lock on the nut and bolt that holds the reed valve together. The reed and it's curved support plate should go towards the cylinder head.

If you don't feel like cleaning the reed valves, just be aware replacements cost over £20 each. I'll go for the cleaning option rather than waste that much money.

Hopefully, normal service will be restored. :D Ideally it's a good job to do while the bike is on a 16,000 mile service as you'll have the cam covers off anyway.


Another Option
To prevent this problem reoccuring, another option is to remove or disable and blank off the PAIR reed valves.
The method I'd use, if ever I did it, is to make four copies of the PAIR reed valve main plates (the ones the seal fits round) to the same dimensions and thickness in a material such as steel (because of it's exposure to hot exhaust gases), but not leave any holes in it. Transfer the outer seal from the original plates to the steel blanking plates and install the blanking plates instead of the reed valve assemblies. Doing it that way means you don't have to worry about removing any pipes and blanking off the airbox connections for them.