B1250 Air Box Mod

Hi Everyone,
OK, I have a problem. I know its obvious but I have to ask. I have been reading the article in the latest AMCN about the B1250 that was modded. In it they talk about opening up the airbox. I have also read the same from the Holeshot guys but in two stages.
First stage is cutting a 1.5" hole in the top closest to the fuel tank and i think also removing the rubber snorkel. Second stage was removing the top case completely but keeping the rectangular base so you can secure the filter in place. Basically having a completely exposed air filter.
I have read somewhere that people have had success with the first stage mod. It allows a throaty induction roar out too.
My question is to those who may have done it, have they had any problems with water ingress into the filter and is it worth the trouble of cutting up the top cover of your airbox?
Mods so far are... 650F, two bros slip on, X-TRE set to gear 4, FI Tuner Pro with Heal Tech supplied map for slip on, X-TRE and AF, K&N filter, running 95 - 98 premium fuel.
Going to do same to the 1250 but if I win lotto or find $1K on the ground would add a pair of Yoshi cams.
Also heard reports that dropping 1 tooth on the front sprocket will liven the bike up alot.
As I'm still running the 1250 in and havent ventured much at all past about 5K rpm, when does it pick up and really haul?

This will all be tuned on the dyno too.

Thanks everyone.

Hi FT,
I can't help with the airbox mod because I haven't done it yet (although there is discussion about it on this forum elsewhere which sounds pretty convincing and I'm tempted). But I can post you my dyno charts (before after the Yoshi R77 was fitted) - photo is a bit average. Apologies for that.
[img][/img]
You'll see there are no real peaks and the low end and mid range are strong and very linear -it just pulls consistently from 3,500 rpm and has a very flat torque curve (basically a very detuned, de-stressed engine that should last forever). It suggests revving past 7,000 rpm is pretty pointless unless you just like to hear the noise! I think I read that the dip at 8,500rpm is due to the secondary butterflys and again there's planty on the forum here about removing them.
Regards

I like the power increase from just the slip on. I just finished putting the F back together from servicing the K&N. I reckon you would get a fair bit of water mist in there riding in any sort of decent wet weather even with the pig snout snorkel installed. The AMCN bike showed a 30% increase in HP over the entire rev range from a R-77 Yoshi, BMC filter with air box chop, PCV and a pair of Yoshi Cams. They reckon it hauls!

I own a fairly modded 1250 and I must say the first thing I did was attack the air box. The induction noise is great and I have never had any water ingress through the BMC filter. Probably the worst side effect is picking bugs out of the filter when you clean it.

+1 for modding the air box

Which one did you do?
1. just remove the snorkle
2. remove snorkle + cut hole in top or cover
3. slice the whole top of the cover off leaving the whole filter exposed.

1 & 2. No need for 3 if the holes are big enough

I'm going to price up an airbox lid from the stealership today. Wreckers won't sell me just the lid. I have to buy the whole box. Sort of makes buying a wrecked bike from an auction attractive.
BTW has anyone else noticed the air intake "trumpets" or "Bell mouths" are different between the 1250 and the 650?
650's are longer (to improve torque) and the 1250's are short (power). (long intake runners = torque / short = peak power)

Don't be shy attack that lid with the hole saw!

I hestitated with my 1250 at first not wanting to cut holes in things etc.

I then grabbed a Yoshi R77 can along with a TFI, O2 bypass, K&N filter & Pairs removal kit (Holeshot-Dale Walker).

I did his stage 1 mods at first........& straight away noticed slightly more overall power but mainly a much smoother responsing engine.

Dale Walker told me from the outset to go straight to his stage 2 tune, but I was very resistant as I'd heard all the horror stories of people having to drill bits after trying to get the throttle bodies out. I also read too much on the interweb of people's differing opinions etc.
I finally succumbed after about 6 mths & removed the throttle bodies, drilled more holes in the airbox & flicked over to DW's stage 2 settings. What a different machine.............more power everywhere & oh so much smoother again.

In a nut shell I don't think you get a huge benefit from just playing with 1 component............you need to do the mods in a balanced, logical way (induction,fuel & exhaust) to get a realistic overall gain.

Then it's suspension ($1500), brake upgrade time (better pads) & you'll end up with a keeper!

But even stock they are a great value & very versatile machine.

Yep, +1 for that. Read my first post - done that and got that shirt for the 650. Just need to get the map fine tuned. VERY happy with it.
Read somewhere that the opinion RE doing the airbox mod to the 650 was overkill as it doesn't pump as much air as the 1250 needs to via the same "pigs snout".

By drilling a 2" (or more ) hole in the air box we are getting more air ,that i get . How are we getting more fuel to go with it ? TFi or P\commander
i expect .How do you know the amount is the correct mix without a dyno run .Does every mod mean another dyno run.? If so this must get expensive.
??

gus wrote:By drilling a 2" (or more ) hole in the air box we are getting more air ,that i get . How are we getting more fuel to go with it ? TFi or P\commander
i expect .How do you know the amount is the correct mix without a dyno run .Does every mod mean another dyno run.? If so this must get expensive.
??

The way I understand it, the airbox mods bring the air intake cross-sectional area more in line with the total cross-sectional area of the throttle bodies (or carbies) combined, otherwise at high revs you're asking a heluva lot of air to go through the snorkel leading to a choke affect. I wouldn't expect a retune to be necessary as low revs performance is not effected just the top end which isn't used that much on the road.

That'll be 2c please.

So i could drill a 2" hole without worrying about it running lean because of no p\comm or similar ?

Plan would be do your mods as close as possible to your dyno tune.
It'll be the best $300 you'll spend to get your bike truly tuned up - then there's no guessing or hoping that it's right.
You can get HP / ftlb and AF mix graphs printed out too for reference save your fuel map or as in the case of the HT FI Tuner, have two maps loaded and selectable via the throttle prior to startup. 1 for track days, 1 for piston burning fuel economy runs.

Gus, I reckon just try the removal of the snorkel first along with a new air filter or clean K&N / BMC etc.

gus wrote:So i could drill a 2" hole without worrying about it running lean because of no p\comm or similar ?

Or u can just buy one to be safe. got my mine from here cheap.

I could afford the "hole" but thats it .Snorkel removed ,secondaries removed , didnt like the K@n ,I'm happy the way it is so ill leave it alone .

" I could afford the "hole" but thats it"....................... ........psst..Gus .... wanna buy a stale donut............ .........Grumpy

The first thing I did to my 1200 was to mod the airbox. Bang for buck, it is THE best mod you can give a bandit. Not long after I added a stage 1 jet kit, but as you have a FI 1250, the computer will take care of it. As others have said the induction roar is fantastic.

This is some basic maths by Grant Beaver on the subject taken from Fast Larry's bandit page:

It's a well known fact that the Bandit 1200 is starved for air by the teensy-weensy airbox opening (originally designed for the Bandit 600). I decided to see just how bad the situation really was...

2" Hole -> 2 inch diameter = 50.8mm = radius of 25.4mm
Snorkel -> 1.5 inch diameter = 38.1mm diameter = 19mm radius
Stock Carb -> 36mm diameter = 18mm radius

(you can already see by this that the 1.5" opening in the snorkel is about equal to the opening of *ONE* carburetor)

single 2" hole area = 3.1416 * (25.4mm * 25.4mm) = 3.1416 * 645.16 = 2026.83mm sq.
Single 36mm carb area = 3.1416 * (18mm * 18mm) = 1017.88mm sq.
1.5" snorkel area = 3.1416 * (19mm * 19mm) = 1134.12mm sq.
36mm area * 4 carbs = 4071.51mm sq
2" hole area * 2 holes = 4053.66

So, the carbs can utilize up to 4072 sq mm of area (at full open). Leaving the snorkel in place (with no other holes in the airbox) gives you only 1134 sq mm of area (less than 28% of what the carbs can utilize when fully open). Using the dual 2" holes gives you 4054 sq mm of area (99.6% of what the carbs can use).
©Grant Beaver 1999

Apologies for the minor hijack.

My bandit is running rich and giving me shitful economy. The TB's were way out but have since been re synched. Would the airbox mod help the bike to run leaner?

The whole power commander route will end up costing $900, which is the PC3 or 5, dyno runs and custom mapping. Just looking at alternatives before I take the plunge. Still running with OEM air filter and a R77 yoshy slip on.

Running rich with can and standard filter.I would think thats unusual ,very unusual .Thats what i run and its not rich at all.
What else is havnt you told us . Have you pulled a plug ,does it look anything like this ?

Just changed my plugs and look the same as yours Gus .

I have a whole in top of airbox lid but still have my secondaries

How olds the air filter Four 40 . They look o.k. till you see a new one .

Do you have a power com Holdenman or simalar.?

No Gus and i wont be putting one on either.

Did the hole in the air box make any difference ?

Replaced plugs last service with Iridium ones. Still running original air filter (16000k) The original shop (CMC) supposedly tuned it on their 'yoshy box' but there was no difference when they returned it back to normal. Methinks I've been led down the garden path with this one.

a bit more induction noise but the only will diffence i noticed was in the high rpms around 7000rpm that it kept pulling hard instead of dying off.