Intake thoughts...

Gents,

Having rummaged around in my underseat area recently, I had a quick look at the intake set up.

First thought, as has been mentioned by others previously, that airbox looks way too small for 961cc of sucking at a high rpm.

Second, ditto for the single air filter in the air box.

Third, the air intake is right under the seat. I know the seat isn’t air tight, but neither is it an obviously good design for air flow either. I can’t see how the intake could suck enough air in for anything other than short bursts of open throttle, any sustained requirement would surely be restricted by the air it can suck from between the seat and the frame rails etc?

I once had a bike on the dyno and played around with the fuel tank position which seemed to me to be a little too close to the end of the velocity stacks for comfort. It was quite surprising to see the measurable difference on the dyno caused by obstructing the air flow somewhat, even though, to look at, you’d think there was plenty of flow to the stacks. This experiment resulted in re-worked fuel tank cos the difference was so marked.

The domi has a larger volume airbox. You could try that with a domi map like 091.

I still say a quality panel filter like K&N , installed at the front of the air box . Just below the breather spigots . This filter could be 20 sq. in. or more and removable in situ. This could even be a factory off road only accessory air box. I will draw something up and post it. The factory might even put in a removable door at the front and you buy the parts to fit the accessory off road racing filter. This would have to be leak free and tight fitting . There would be 4 or more fasteners (molded in threaded nuts ) and a simple perimeter frame to hold it tight. and the best part is the bike would still look clean from the side view. You may not even notice it.

Fast Eddie said:

First thought, as has been mentioned by others previously, that airbox looks way too small for 961cc of sucking at a high rpm.

Second, ditto for the single air filter in the air box.

Third, the air intake is right under the seat. I know the seat isn’t air tight, but neither is it an obviously good design for air flow either. I can’t see how the intake could suck enough air in for anything other than short bursts of open throttle, any sustained requirement would surely be restricted by the air it can suck from between the seat and the frame rails etc.....

Click to expand...

Nigel,

I agree will all of this.

Because of this same type of classic bike design - airbox behind the engine intake, the Hinckley Bonnevilles have a similar barrier to developing good engine breathing. Most Bonnie owners just yank the airbox out and install sock style foam air filters on the carbs or throttle bodies. Of course the Bonnies have side covers that can be replaced to cover the ugly void of the missing airbox, the Norton does not. The EFI Bonnie guys neuter the airbox sensor by installing a resister in place of the airbox temp sensor.

I think this same technique can be used to free up the 961's induction, but it would then be necessary to install a catch bottle for the engine breather, and fabricate some manner of faux airbox/side covers to maintain that beautiful 961 profile.