Q Why is my Bonnie rich on the right?
If we don’t know the answer, we’ll find the person who does
I have a 2009 Triumph Bonneville 865 EFI SE that has decided to run rich on the right-hand cylinder. The bike does have an aftermarket exhaust fitted, but ran fine for a week, so I do not think that is part of the problem. I only noticed it when I removed the Secondary Air Injection (SAI) system and checked the plugs. It seems to be only at low revs or constant throttle when it causes the plug to go sooty. The 12,000mile service is due in a few hundred miles. Oddly, the left-hand side runs perfectly. If it was a problem with the SAI or lambda sensor would the engine light not come on? Pete King, email
Answered by Clive Wood, Clive Wood Triumph It’s possible the lambda sensor has failed, but it’s more likely to be because the SAI has been disconnected. SAI has been around the Triumph range since 2001 to clean up hydrocarbon emissions by bleeding air into the exhaust system. On the Bonnies it’s a reed valve block under the fuel tank that’s controlled by a solenoid. Most owners of carbed Bonnies remove it and blank off the piping because it’s an added complication, can blue up the exhaust and there’s no emission test at Mot-time (yet).
But on a fuel-injected bike it’s linked to the ECU, which is also getting data from the two lambda sensors in the pipes with different modes for low, medium and high revs to work in tandem with the catalytic convertor. The sensors will expect to see 14.5:1 air/fuel ratio as that’s where the cat is at peak efficiency, but if the SAI is disconnected it might see 13.5:1 so it tells the ECU the AFR is too rich and leans it out. Take it back to standard first to diagnose the fault.