Bonnie Air Filter Mod

Bonnie Air Filter Upgrade.

I decided to tweak my carb'd 790 Bonnie a bit.

When I bought the bike it had already had the SAI removed.
I have installed a tors exhaust which have been on sale from the dealers (my local is the Ashford Jack Lilley).
I have upped the main Jet to 120.
Fitted a DNA free flow filter, a cheaper bell mouth mod than the ones you usually see for sale from the various online retailers and de baffled the air box.
It now rips along and the mid range is "fabulous" as they would say in the valleys.

My reason for this post is to let you all know about the cheap bellmouth / velocity stack mod I have done which I have to say is not my idea but one that people on the other side of the pond have done.

The part used is a Polaris snowmobile air intake which although readily available in the states proved quite hard to source here in the U.K.

 

I managed to source one from this company TME,
http://www.turfmachineryengineering.co.uk/

It is very easy to fit, you do have to trim the side that fits inside the air filter with a pair if scissors though but the rubber is very soft.

Here are a few pics

 

Now the best bit
Half the price of those on offer from the various retailers.
TME have now become the sole U.K. Polaris snowmobile distributor.
So if you want to buy a snow cat you know where to go but they will also sell you a small piece of rubber to stuff in your Bonnie which they will mail order to you.

 

I also took the baffle out of the air box which I had been putting off because various people had commented on how it was a bit of a pig to do.

Well Don't Put It Off.

It is not that difficult at all.
What I did do though was take of the rear shocks so I could drop the back wheel down further to give me more room on the high up screws near the seat.
I also took off both sides but you only need to take off the right side (rear brake side) to be able to pull out the baffle.

The bonnie now really does pull very well indeed.
I did fit a DNA filter which has cost about £50 but the bellmouth and de baffle is a very cheap / big gain mod.

Jonesie chuffed with my fettling

 

Must admit Valkman I did think about doing that way but everything else around it will heat up, you could in effect distort the air box.
The peeps a TTP probably having done a few know the exact spot to heat up.

Here is a step by step TTP link on how to do it,
http://www.triumphtwinpower.com/triumph-twin-easy-airbox-baffle-removal.php

And here is the bit you are aiming to release from the box with the arrow being the direction you want to pull from.
The arrow is on the right side/rear brake side.

 

The baffle seems slightly thicker, sealed the box up by putting a thin bead of silicone in the gap between the cover and main air box body.
The cover slots into the air box body and you only need a slither.

 

Yeah you are probably right I will need to up the jet size.

Here is a brilliant link to the Jenks web site although I think the business has ceased trading...
http://www.bonneville.se/nedladdning/Hur man jettar.pdf
Scroll down to the bottom and there is a great jetting guide.

Just as an aside the original Jenks was Stirling Moss's co driver when they won the Mille' Miglia road race way back in the 50's.
Jenks invented the pace note system using a bog roll (which were awful things back then, greasy nasty things.)
He wrote the entire route on the bog roll and then unrolled it as they screamed along, never lifting his head up once to look over his fly screen.
Although he is mainly known for his exploits in the Mercedes with Moss he was really a biker and had a huge collection of fettled Nortons and Triumphs a few of which have made their way to Brooklands.
He also wrote for motor sport for years.

My mate bought his old house, it was really a collection of interlinked workshops being the bachelor of the parish he was free to fettle and not be tainted by the demands of SWMBA.
Every part being stuffed to the gunnels with anything and everything to do with motoring on either two or four wheels. Suppose it was the motor jumblers form of paradise.

The cup he was presented with when they won the Mille over the years had disappeared, Jenks had no idea what had happened to it much to the disappointment of a motorsport historians as it was a part of motorsport legend....

When my mate was clearing the house out before he pushed it over he was wading from room to room sorting stuff out with the Brooklands people.
Eventually they made it in to the bathroom and the Brooklands people said "nothing much in here let's crack on" my mate still to this day not knowing why said " hold on a minute as he has stuffed things in every nook and crannie, (wheels under his bed, carbs in boxes in kitchen cupboards as opposed to food,) let's have a look under the bath."
He duly took off a scanky bath panel and there was the cup holding up the bloody bath!

Here's his Wikipedia link
https://en.m.wikipedia.org/wiki/Denis_Jenkinson

Sorry to digress.
Jones the historian ha ha

 

Spoke to TTP and he recommended a 135 main which is now installed.
It seems to have removed the occasional pop when blipping the throttle from idle.