Airbox questions.

[plodalong]

My thruxton with a TORs, Norman hyde bell mouth, Dna airfilter, restrictor removed, 1 shim on the needles and 135 main jets (actually 126 DJ jets) gets about (at least) 10% improved fuel economy. When I first got it with just the TORs I got 160-165 klm to reserve, now I got a worst of 191 klm and best of 215klm to reserve. Shes got a much better midrange and hits the rev limiter (8200) in 4th easily. You dont realy need the bellmouth just cut the filter cover where the snorkle was to the same shape as the filter opening. Only reason I got the bell mouth was I like to be able to put my bike back to stock even though i probably never will.

 

[FoothillRyder]

My thruxton with a TORs, Norman hyde bell mouth, Dna airfilter, restrictor removed, 1 shim on the needles and 135 main jets (actually 126 DJ jets) gets about (at least) 10% improved fuel economy. When I first got it with just the TORs I got 160-165 klm to reserve, now I got a worst of 191 klm and best of 215klm to reserve. Shes got a much better midrange and hits the rev limiter (8200) in 4th easily. You dont realy need the bellmouth just cut the filter cover where the snorkle was to the same shape as the filter opening. Only reason I got the bell mouth was I like to be able to put my bike back to stock even though i probably never will.

What I noted with my Thruxton was that when new and stock (everything), it would run out of breath at higher revs in any gear. It would struggle to get to the limiter in 3rd, and would never get there in 4th or 5th. Just changing to the TORs and a K&N filter completely transformed the bike. I SLAMMED into the limiter in 4th, and climbed easily to the limiter in 5th (indicated 130mph). I pulled the snorkel and the restrictor and changed to 130's, swapped the igniter box for one with a different curve, higher limiter, and a bit more advance, and got 67.5 hp at the wheel.

They absolutely strangle these things at the factory.

 

[sportyone]

My thruxton with a TORs, Norman hyde bell mouth, Dna airfilter, restrictor removed, 1 shim on the needles and 135 main jets (actually 126 DJ jets) gets about (at least) 10% improved fuel economy. When I first got it with just the TORs I got 160-165 klm to reserve, now I got a worst of 191 klm and best of 215klm to reserve. Shes got a much better midrange and hits the rev limiter (8200) in 4th easily. You dont realy need the bellmouth just cut the filter cover where the snorkle was to the same shape as the filter opening. Only reason I got the bell mouth was I like to be able to put my bike back to stock even though i probably never will.

I feel sea levels have a fair bit to do with performance mods etc,
what sea level are you at ?

some guys in the states are at 3000+ so one can't go by their jet sizes etc much either. their fuel octane is even different too!

our bikes come standard in Australia with 110 jets I think, 115-120 I believe is about normal with open flow pipes and no snorkle, but ecomomy suffers though from there !

 

[plodalong]

In Australia everything is near sea level, GPS says 160 metres, Approx 500 ft. I tried
130s and 132s, not much difference but stuck with the 135s. Plugs look good and engine is running cool, even on a hot day the oil temp dosn,t get much over 90 degrees c. Then again I don't sit in traffic as there isn't any to sit in.

 

[sportyone]

In Australia everything is near sea level, GPS says 160 metres, Approx 500 ft. I tried
130s and 132s, not much difference but stuck with the 135s. Plugs look good and engine is running cool, even on a hot day the oil temp dosn,t get much over 90 degrees c. Then again I don't sit in traffic as there isn't any to sit in.

wow, that seems a big jump from the 110s standard jets,
& you say, you still getting around 200 klms out a tank ?
I'm getting that too ,
but, I was told if I were to go with 115s my fuel would suffer to around 170 klms per tank ? pretty confusing I say.

only reason I'm asking is after my dyno result at WOT from 2500 rpms in 4th, it showed some leaning off around 4000 to 4800 rpm & again @ about 7000 rpm so they never took it to limiter ?
air/fuel started around 14 to 3400 rpm then rose steadily to 15 @ 4400 rpm then sat between 14 - 13 before heading towards 15 again from 7000 rpm.
I don't mind using more fuel if I'm going to get more go, most of my riding is just cruising about though with the add squirt now and then, after all I don't
and can't run it too hard these days with all the cameras about & police blitz's on

 

[plodalong]

Yes the standard airbox with the snorkle and "restrictor" limits the flow somewhat. The NH bellmouth or just cutting the airbox cover where the snorkle normally resides to the same size as the airfilter opening along with a high flow filter (DNA and UNI seem to be good) will let the engine breath better. I had 125 mains with this setup and economy was a bit better than standard, But removing the restrictor really opens it up and needed the bigger jets. My bike came with TORs but the standard 110 jets, I fitted the 115 mains and didnt notice any change in economy (or performance). The only possible downside is you get an increase in induction noise which I quite like but it might not suit everyone. For me it was worth the effort.

 

[ivar]

When I got my bike it had Tors + 115 mains. 48-50mpg when touring at 50-70mph. Then swapped to a uni-filter, yanked snorkle and put in 120's + 42 pilot jets. Mpg's stayed the same for the same riding style.
Then went to the TPUSA ARK,pod filters, 145 mains, 1 shim on the needles, dominator touring pipes. Mpg's still at around 48. Usually switching to reserve at 200-220km.

What I found really killed my mileage was when I put in richer needles.

IMO, with these breathing/power enhancing mods, the bike will make the same power at lower throttle openings, so it won't neccesarily use more gas because of bigger jets.
But then of course, when this extra power is utilized - the bike will use more gas than before , to make more HP

 

[Keith Harding]

Over the Christmas period I took the opportunity to pull the restrictor plate from my airbox.
When I bought the 07 bike four years ago the original owner had replaced the standard exhaust with a Staintune one.
I pulled the SAIS, removed the snorkel and fitted a K&N - all of this helped but from reading about the airbox on this forum and personal hunch I still felt that the bike needed to breathe a bit.
The Airbox removal thread provided a lot of good info so using that I set about opening the damn thing up and getting the plate out - it took me a while and a wee bit of free-form cursing but it came out.
I was pretty keen to see if the original owner had rejetted the carbs when the Staintunes were fitted - he had not - 110 mains were still in there. I refitted with 125s and also replaced the carb screws with the BC stainless screws - much better.
The bike started first time and feels as though the breathing is significantly improved - fuelling at a low city speed feels much smoother too.
Thanks to all on the forum for useful advice freely given. My contribution to that would be that when removing the airbox screws on the right hand side, don't leave the two behind the rear frame until last - they are real buggers to get out but it is a little more easy to get at them when there is tension on the box from the rest of the screws.

 

[PieMan]

Keith, your bike will most probably run better with 132 main jets, the 125's are a little small with the airbox baffle removed.