Bike of the month June 2018

May and June have been busy months for the OSS Admin team. Endurance legends at Donington followed by the TT and even some highland scratching thrown in for good measure. So OSS site time has been limited. (OK excuses for late BOTM out of the way)

Three years ago I wrote this article about a long time member who had long held a dream of building an engine that he had been quietly collecting the bits for .It may have escaped the attention of some, but not me, that he actually built that engine this year.

He didn’t just build it for fun either, he built it to compete at the Donington 4 hour endurance race, against some pretty serious competition.

What is even more special about this bike is that the builder found out early on in the build that he been diagnosed with prostate cancer. Lesser men may have chucked the towel in right there and then but not this guy. He was too busy for cancer and decided he would postpone his treatment so that he could finish the bike and compete on it at Donington. The stuff of legends, I know.

In the end the minor inconvenience of a life threatening medical diagnosis must have momentarily distracted him because although this bike got finished there just wasn’t enough time to get it match fit. Our man still competed in the event along with 2 other OSS team members but it was on the back up bike (not a Suzuki)

Now that John has completed his goal of competing in the endurance legends round at Donington his treatment can begin. He hasn’t wasted any time in making some big life changes including selling all of his bikes and parts. I know that he still has the GS though and I hope he keeps it and gets it to run the way he knows it can.

John you are a Legend mate and we love you and your GS is bike of the month.  You are also the only man in OSS history to have been awarded bike of the month 3 times.

Read John’s build here

Members discuss this here.

It’s never too late to be what you might have been- A winged hammer’s tale.

From time to time we lift a story from our forum and put it here for the wider world to enjoy. This is one of those occasions. Mole is one of our winged hammers and if you ever found yourself wondering whether it was too late to take up track racing or thinking you needed mega-bucks just to get started, Mole’s story should provide some inspiration.

What started as a bit of laugh has seen Mole win his local class championship and this year, Mole will take on both Donington’s classic endurance round in May and Spa in June.

This is Mole’s story, so far…

 

 


This is how it all began. It was Christmas 2012.

I had a perfectly mental, tuned GSXR thou and I got talked into going racing. After all, I was 46 and if I didn’t do it now, I never would. My mates were racing in the Post Classic series and, if I wanted to take them on, I needed a pre ’88 bike to do it on.

I got £1200 and the horrible 750 Slabby streetfighter you see below for my pride and joy(oddly I don’t miss it).

It was standard apart from the Blandit 600 wheels, carbs and a really loud,rattly can. The weird seat unit looked ok but weighed a ton. The brakes were knackered and the motor was seized.


I had 3 months to turn it into a competitive race bike.

Not having a clue about racing didn’t help. I looked on the web at racing Slabbies and dreamed of world championships. I looked at frame mods as I had heard that the standard frames were far too flexible. I got some 6mm alloy plate and a length of 40×20 box section and made up some bracing. I don’t have the capability to alloy weld so I taped them onto the frame and took it to the local blacksmiths to get welded up. I bought an aftermarket fairing on Eblag then realised that it didn’t meet the catch tank regs so pop riveted a bit of caravan onto the bottom. I made a couple of brackets to fit R1 calipers to the Slabby forks,fitted clipons, an R1 shock, an 1100M back wheel, painted it matt black and poured diesel down the plug holes. After a couple of days it was turning over and running on a set of VM29s that I already had.

I was ready for action.

Season 1

As I said, I didn’t have a clue about racing. My mate Iain P was coaxed into helping me. He was in strong disagreement that the best way to find the limits of adhesion was to lean more and more till I fell off (both left and right). But that’s what I did. My first race was at East Fortune. I did a 1:17 and fell off. The bike felt horrible, Skittish and downright dangerous in the damp with road legal tyres as we weren’t allowed wets. Not helped by the fact I was running them at road pressures of 36 front and 42 rear. When I asked someone about it they pissed themselves laughing and told me to try 31 front and 28 rear. What a difference that made!

There were 15 riders in our class and by the end of the season I was down to a 1:08 and finished second in class.

Season 2

Second season and I had made a few changes.

I bought another fairing and took all the bodywork to my mate Wee Stuart the painter and told him to paint it the same colour as the car I was getting sprayed. The car looked better! I got dogs abuse all year about that colour. Luckily enough I crashed it at the last meeting of the year so it would need painted again. It got a Gsxr600 K1 front end with a ZX9 wheel, fireblade calipers and a shortened random, and much more sociable, end can. All much cheapness as money was tight. Best buy was the Taiwanese rear sets. £36 and made from an alloy I had, and have never since, encountered. They crash really well. When bent double they can be hammered straight again and again. I decided to go with no proper seat as comfort is the last thing on your mind when racing.

It was tight that year, but I won by a handful of points.

Season 3

Season 3 and I have a target on my back!

The team: Jools-Team principal- cook

Iain P-Crew chief- Prophet of Doom

Me- Ballast-Talent(depending on results)

The big change for this year was my mate Andy Fyffe bought me a set of PFM discs. He has the superbike ones on his Harris Magnum4 and swears by them. He’s not wrong., Combined with Bendix carbon matrix race pads, they are like hitting a skip!

I bought a second hand stainless race pipe and can, some cheap chinese levers, a kid on seat and new paint.

A proper race loom was made up and doubts were cast as to the longevity of the still original de-seized motor(as can be seen by the amount of oil on the tailpiece)

There was no way I was going to win this year after a couple of crashes(silver Gaffa tape is my new best friend)

As luck would have it, Andy Lawson who was sure to beat me, went off to do the Manx (and won his class) so that left me winning by a handful of points again this year(2014)

Season 4

First major revamp. I bought a load of Gsxr bits from someone who was moving class to supertwins. The package came with a blown 750m motor with a lightened and balanced crank and a Wiseco 771cc kit. It had dropped a valve and destroyed the head and piston but the cylinder was untouched and came with a new piston kit. Also in package was a low mileage 750m motor and a Dyna 2000 ignition set up. Because I’m a slack arse, I decided to put the complete 750m motor into the bike along with the Dyna ignition and find another head, to get ported, for the trick motor for a later , more points demanding stage in the championship. The Prophet of Doom was in total agreement, much to my surprise,but only because he doesn’t like change. A new swoopy slingshot body kit was purchased. Again only because it was £100 cheaper than a Slabby one. At least the people that make “race” fairnings reckon that you will need a full belly pan for a Slingy. Painted it myself this time. Looks fabulous from a good few feet away. Changed to 36mm CVs( forgot to mention that the year before I had the VM29s bored to 33 at the back to match the fronts). The 36s used less petrol which worried me.

I put Hyperpro springs in the forks which greatly improved the handling. Unfortunately this meant I started having ground clearance issues. I moved the pegs up and back a little, made a new link pipe for the exhaust to tuck it in and cut holes in the fairing where the bulges for the engine cases were.

Halfway through the season is when the electrical gremlins joined the team. The bike would seem fine for about 8 laps of the 10 lap races then start misfiring. We kept finding dodgy connections (caused mainly by using those shitty blue connectors). We would think it was sorted but it would do the same thing again. We changed the plugs, the coils, made another loom and even tried a better fuel tap in case it was petrol starvation. Nothing seamed to make a difference. It was at one of the spark plug changes (last race of the weekend) that a rogue (and tiny) nut had found its way down the plug tube so that when the plugs were taken out, it fell in. The motor sounded terminal on startup so the bike was put in the van. The trick motor was put into service by using the head from the standard motor. That’s when I noticed the tiny square nut embedded into the edge of the combustion chamber.

The rules were still the same regarding tyres. Road legal only. No wets. We were running Pirelli diablo supercorsas in the dry and Michelin pilot road 3 touring tyres in the wet.

I’ve ridden bikes all my life and most of it in Scotland so riding in the rain doesn’t bother me. This worked well in my favour as it was wet a lot that year. I won the championship by a fair bit and went the whole season without crashing.

Season 5

 

The class was beginning to dwindle with only 8 bikes left. The racing was still good though. My main rivals Gordon Murray on his VFR and Gordon Castle on a very well put together Gsxr 750 were always right with me. I was still having ground clearance issues because the bike was handling so well. The NRC casings were getting scuffed as was the fairing although I had pulled it in as much as possible. I made up brackets to move the top mount of the shock back and down which meant I had to take more meat off the linkage to allow more height. They look dodgy and I meant to get them welded onto the frame but never did and they haven’t moved. I should still get them welded on.

Deek had joined the team as pit crew and moral prevention officer. Mostly he noised up the competition.

At the Bob Mac Memorial classic races that year I did my best ever lap of 1:03.7. This was only possible because of the perfect weather conditions and having a couple of world class riders to chase. I never beat them but they dragged me along a full second faster than I had gone before.

Wet tyres were allowed! They are epic. If you have never tried them you wouldn’t believe how grippy they are. I prayed for rain and did my rain dance every meeting.

The gremlins were still on board. I was over riding the bike when it was stuttering on the last laps and ended the season with a couple of crashes. The bike was fast though and I could build up enough of a lead to still finish 1st or 2nd. I managed to win my fourth consecutive title. Just.

Season 6 2017

I had been warned not to run the number 1.

What do they know!

Over the winter I had bought another motor that had just been built by a renowned tuner. It had Wiseco high comp pistons and a ported head. Unfortunately for the guy his fuel tap had not shut off and filled the cases with petrol resulting in a big end failure. We made an engine up from all the best parts we had. It’s a total screamer. New paint and another end can and we were ready.

First race of the year and the bike died after 3 laps. When the race was over it started and ran perfectly back to the pit.

We checked everything we could think of. I was told the Dyna 2000 ignitions were bomb proof and no way it would be that. I didn’t have another one anyway.

The class was only 5 strong and we were out with the CB500s. It meant we only got 2 clear laps before we were in traffic. That worked in my favour as the bike was still playing up and I managed to finish 2 of the races.

I was convinced that it was a fuel starvation problem so for the 2nd meeting i bought new Mikuni RS34s and fitted a Pingle tap. On a sneaky test ride along the back roads the bike felt great and never missed a beat. At the meeting on the practice session the bike ran perfectly. However when the call went out for qualifying it would not start. No spark.

One of my rivals lent me his spare Dyna ignition. That was the problem all along. I had to start at the back of a 36 strong grid (30 pizza bikes and then the post classics). By lap 5 I tried to take the lead and crashed. Bugger! It had ripped all the controls off the left side of the bike. We had enough spares to sort the bike and hammered straight the unbreakable Taiwanese rear sets. 2nd race and the gear linkage snapped on lap 2 and in 5th gear. I finished the race but burnt out the clutch slipping it out of the tight corners. I didn’t have a spare clutch so I roughed up the steel plates. It was better but still slipping. 2 distant 5th place finishes.

I could still win the championship (theoretically) if I won every race.

At the 3rd meeting everything went perfectly. I won all the races and my nearest rival had a DNF. It was on.

Last meeting of the year. First race. Pole position. The lights went out and my throttle cable snapped.

Fixed the cable by soldering a new nipple on. 2nd race. 2nd lap and the cable snapped again.

It was over.

Won the last 2 races but finished a distant 2nd in the championship.

Good riddance number 1 plate.

Roll on 2018.

Mole.

If you are interested in learning more about our winged hammers or if you are a potential commercial sponsor and you would like to get in touch with any of our winged hammers please sign up to the forum here

Bike of the month February 2018

Oh no, here he goes again, twittering on about “evolution , not revolution” and “genetic engineering of an extinct species”

Well, nearly but not quite. I’m going to mix it up a bit this time and tell you a tale of evolution AND revolution.

Back in the Dino days of the old site there were many lovely bikes built but because they were scattered around the world you didn’t always get to see them in the flesh. I travelled a lot for OSS and I was lucky enough to see quite a few, close up. Some lived up to the hype and some didn’t. (I include my own creations in the latter category)

As luck would have it though, I didn’t have to travel far to see a bike, where the opposite was true. The pictures I had seen of this bike online, before I stumbled across it at a local bike meet, had not done it justice. That bike belonged to Gregg Campbell AKA Wee Man.

Looking around Gregg’s GSXR1100M Slingshot you could just tell his had been a long and intense love affair. It had the look of a bike that had been tastefully, and carefully evolved to meet its owners exacting tastes and requirements. All of which, were very tidy and meticulously well executed. If our FBOB had been there, he would have been forced to say “bugger me that’s shiny”. It instantly got my “bike you’d most like to take home” vote.

“But KM you promised us a revolution as well as an evolution!”. Easy tiger, I’ll get to that bit.

Fast forward a few years and I’m loafing around at the Fast by Me workshops drinking coffee and listening to Dave telling me about how he took an angle grinder to his modem, while on the phone to his internet provider’s customer support line. Out of the corner of my eye a familiar bike caught my attention. It was none other than Gregg’s Slingshot. “I know that bike” I said. Now we all know what happens to anything that goes to uncle Dave’s. That’s right, it gets the boost.( unless it’s a faulty modem)

The boost is pretty much Dave’s solution for everything ( I think he’s onto something). Gregg’s Slingshot was in for one of Uncle Dave’s rock solid turbo kits. Even Dave paused his internet tirade for a moment to chip in how tidy the bike was.

I’m sure Gregg will agree with me that the arrival of “the boost” has been anything but evolutionary and every bit Revolutionary! (made it, see)

This tells you all you need to know about limitless possibilities offered by 80s and 90’s Suzukis. The best part of breaking up, is making up, especially when the making up bit includes a extra-large bucket full of lairy charged up horses.

Gregg, congratulations you’re our bike of the month.

Members discuss this here.

Bike of the Month January 2018

Unicorns and cannon balls and Aquagenic urticaria

Here at OSS.info we have our ‘sections’, and of all these the newest kid on the ol’skool block incorporates the water girls and water boys. Their choice of OSS machinery would, to the untrained eye, appear to be frowned upon and the butt of our communities ‘real ol’skoolers’ jokes, almost as if they’re are just about tolerated.

Madb didn’t let this ‘strange arrangement’ phase him, and got on with sharing the pursuit of his own wet dream in the mother of all sections.. ..’projects’.. We all love this section and the numbers prove this, so jumping in at the deep end like one of Pumhart von Steyr’s wet farts would come as a brave move to the unskooled-ol’skool, could there be a more obvious username? too far? too soon?

Here at OSS.info we have no need for toleration, these four concepts and their paradoxes are taken care of by RTFR and the sites definition of ‘what is’.  Armed with this OSS.info and an ethos that I’m sure many of the ‘project pool party’ be them oiled up or blow dried could identity with, has set about making positive evolutionary progress rather than chasing the elusive ‘wheelie wire’.

To say OSS.info tolerates anything on the site would be an insult to both parties, the site’s boundaries are set for all to see just RTFR, and In these boundaries in my own OSS.info virtual dream garage I’m in the centre (OBVS) and every members bike(s) on this site are top-trump cards fanning out, inadvertently jostling for a close orbit but for unknown reason (to me) the water boilers have to work a little bit harder to grab my attention, this bike’s gone from a weak blip on my paris dome to an active target with zero bearing rate.

congratulations Madb, your life and times gsxr is BOTM. The drinks are on you…….. Julie Andrews for me, and that’s almost as close to hobnob humour harbour as I’m comfortable with, so let’s drop a ‘boat anchor’ here before sun down….full moon….half moon…..total eclipse…..that’s it…. my bourbon biscuit built boundaries be breached.

Read Madb’s build thread here. Members discuss this here

Bike of the month November 2017

If you want to shed a few pounds, some say the best way to do it is to cut down on your carbs. Apparently, if you’re really serious about getting all lean and mean you need to cut carbs out of the equation completely.

Now personally, I use whacking great RS36s on both of my big inline four Suzukis, which might explain my shrinking leathers- or not…

Anyway, here at oldskoolsuzuki we are purveyors of the philosophy that 80’s and 90’s Suzuki muscle bikes can be improved, while preserving their adorable  “fuck you” characteristics, by doing clever things with parts from the future. This months podium goes to a bike that ticks all of the above boxes.

At the heart of this braced ,steel framed Katana ensemble is the full fat, mighty air-cooled, 16 valve, GSX engine which has been tweaked up to 1170cc. It sports a complete EXUP front and back end too. Sounds tasty, I hear you say. “but what about my abs katanamangler?” “I’ve got a beach holiday coming up!” Well, worry not my middle aged,weight watching friends, this one is completely carb free! Yeah, that’s right, you heard me!

Using a a set of GPZ1100 throttle bodies and a set of GSX1400 injectors, our man Skelly has taken all of the guilt ( and a fair bit of hassle) out of 80’s muscle bike addiction through the wonders of EFI.

The bike was test ridden by Jon at our Donington Park track day gathering in August and it ran well.

Congratulations Skelly, your guilt free Katana is our bike of the month. Read more about Jon’s build here. Members discuss this article here.

 

Bike of the Month September 2017

Goodbyes are never easy but they make for a good occasion to honour something or someone that has done OSS (very) proud. Let me fill you in…

Maxwin stumbled on the scene in January 2016 mid-development of his 750ET after having competed in the 2015 season of the Earlystocks championship. Having cobbled together the bike for 2015, the early days of 2016 were there to fine tune the bike and get it all working a bit better, looking a bit nicer and going a bit faster.

As with pretty much every build I’ve ever seen on OSS, thing spun a bit out of control with lots of clever engineering, pole positions and ultimately, big crashes. If you’re not crashing, you’re not racing. There’s no argument to say our friend Maxwin didn’t try his very best.

One of the very first to be promoted to OSS Winged Hammer, he has kept us up to date with all the ins and outs of the ET, plenty of pictures and YouTube videos for us to ogle over and wish for it to be us on the clipons and having a go ourselves.

Personally, I’d love to go racing, but lack of talent/balls/money will see me get my fix trying to hassle my bike around during rookie-level trackdays, dreaming of keeping up with the likes of Maxwin and his Earlystocks-compadres.

But, this is a goodbye, and for OSS an instance to honour someone who in turn honoured our request to fly the Winged Hammer flag and do his part for our little community. After a few heavy crashes, our friend choose to follow the path of progression (as you do with racing) and that progression sees the ET and Maxwin parting ways, with a water-cooled 600 of a not-to-be-named brand waiting in the wings to bring new highs in the career of our friend.

Update: It will be a Slabby 750 for next year, hurray! The ET will stay and progress, for Maxwin keeping it and let his dad have a go.

If you’re not crashing, you’re not racing. If you’re not trying to take things to another level, you’re not racing. If you’re not out to get that next second off your lap time, you’re not racing.

Maxwin chose racing and thus, we must say goodbye but not before we award him with the BOTM September 2017.

You sir, have truly done us all a big favour by letting us enjoy your updates and it makes me personally very proud to see our stickers on bikes used as intended and doing a bloody good job at it too! Thank you, I hope you return into our fold at some time in the future, for now, all the best 🙂

Congratulations on Bike Of The Month September 2017

Buildtread here

Turbo Kits and Performance Parts

loopy pic 1Fancy websites and a huge social media profile are all nice and dandy but the real recommendation for a craftsman’s work is in the examples you see, hear and touch and … if you’re really lucky maybe even experience. When it comes to the FastByMe HQ, there is no shortage of examples at varying stages of turbo-ness in build state, power and career path to get a good feel for what performance enhancement is right for you. The enthusiasm and downright bloody-mindedness that can’t see any reason why all motorbikes shouldn’t have one radiates from the King Pin of the operation Dave Dunlop who is supported by his ever patient wife, Samantha.

Tucked away in the now not-so-quiet confines of a sleepy Rutland village, Dave can be found slaving under the Fast By Me banner as he has done for many years. We’re not quite sure how many exactly, but the doctor’s note was issued before word processors. Long enough is a good answer.

Dave predominantly creates custom turbo solutions but extends his offerings to other performance parts including billet big blocks and cam oil feeds as well as a range of tshirts and hoodies to wear when you’re going really fast. For more information and a range of live action videos, check out the website www.fastbyme.co.uk

 

loopy pic 2

loopy pic 3

 

loopy pic 4

loopy pic 5Dave will be offering a 10% discount to OSS members for complete turbo kits so don’t forget to mention the site when asking for a quote.

As an official introduction on the site, Sam is offering a Fast By Me hooded sweatshirt to the person who can identify how many times FastFurby can be found on the website www.fastbyme.co.uk

Send your competition entry over to terriblethunderlizard@gmail.com – closing date 30th September – get counting!

Fitting a 916-style Steering Damper

By Banoffee.

My slabby has a lively front end, so I’ve been wanting to fit a steering damper for ages. I even acquired the period Daytona fitting kit and damper however couldn’t get that to work with my USD front end. So, seeing as I wasn’t keen on modifying the frame to take a bolt-on side mounted damper the only option left was a 916-style fitment. Seeing as I’m running an Ohlins rear shock, the damper had to be Ohlins to match of course!

Basic theory:
Whilst steering damper manufacturers don’t list fitting kits for oldskool bikes, it’s actually a simple matter of taking the measurements and then doing some research to find a suitable kit (or parts from several kits).

The measurements: (Note – some measurements are taken with internal vernier edges, some external. These are just shown to illustrate, you should of course check your own measurements carefully!)

A: Yoke nut centre to tank front mount centre

AB: Top of tank mount to top of top yoke

BC: Between centre of tank front mount bolts

CD: Between LH lock and centre (then multiplied by 2)

DThe research:
I took a tape measure with me to bike meets, bike shops etc to measure up more modern bikes (with owners permissions of course when they were about!) and also bothered a few people selling kits on ‘that auction site’.

My bike:
(750G with 400gk76a USD front end)
A: approx 50mm
B: approx 60mm
C: approx 50mm
D: approx 60mm

Things to note:
On my slabby, the damper is quite close (5-10mm) to the tank. Double, triple check all measurements to ensure it won’t foul anwwhere.
Source the fitting kit before buying a damper so that you can mock up and modify if necessary. Setting a good search on ‘that auction site’ makes this surprisingly easy and cost-effective.
For the damper stroke, obviously err on the side of slightly longer but not too long as it will look unbalanced.

The result:
I picked up a 2000-model H*nda Firebl*de Harris fitting kit from ‘that auction site’ for a whopping �20. Measurements were near-perfect as a 1-2mm on the tank mount, etc. is just fine. Only slight drawback was 30mm lower ‘B measurement’ so I acquired a 30mm tubular spacer.

EMy ‘D measurement’ (remember to multiply by 2 of course!) meant an approx 60mm stroke damper so I ordered a 63mm stroke Ohlins damper from BikeStuff (cheers Rich!).
In the pics below you can see the finished result. I’ve lost a tiny amount of right-lock, however, eventually I’ll get a spacer made up to under the tank-mount part which will solve that. All-in-all I’m well pleased!

245

Journey to the center of Mikuni’s BST38SS carbs

Journey to the center of Mikuni’s BST38SS carbs.

When I was studying my new 38mm slingshot carbs my eyes fell on the small rubber hose which runs along the outside of the carbs from the float chamber to somewhere above the intake. I disconnected the hose and started tracing the circuit inside the carb.I did this by reconnecting the hose to one of the fittings and bowing into it. So by hearing where the air escapes you know the routing of the circuit.bst38ss-1

The top fitting connects to the uppermost hole in the bellmouth, but when I blew into the fitting of the float chamber I seemed to have hit a dead end because there wasn’t any air escaping. I noticed a small plug which looked like a jet inside the float chamber. I removed it and now I could blow trough it. First I thought the jet had been clogged but after closer inspection it really was a plug instead of a jet. So there was a hole in the bellmouth that connected to the float chamber, but the hole was plugged. I had some sleepless nights trying to figure out what the function of this would be.bst38ss-2

Then I decided to do some investigation on the web. I didn’t expect to find much info on Mikuni carbs on the web, but suddenly I found this article deeply hidden inside Factory Pro’s website…


Power Jet Circuit, GSXR750, as installed on air cooled gsxr750 w/ 38mm Mikuni carbs, 90-92

Power jet carbs – Mikuni’s great addition to a carb used in a high rpm application.

The power jet adjusts high rpm mixture, in the gsxr750 – from 10 to redline, in 1/3rd the step of a main jet change. Changing a main jet, in the 38mm carb, as installed on the gsxr750, adds or subtracts up to 2% CO per main jet change – when the CO% needs to be adjusted in in .2%-.4% for best power attainment.
Changing the power jet allowed much finer increments of change and, just as critically, happened to change the fuel delivery curve to what was optimum for the gsxr750 – something that would have required main air jet changes and other modifications to attain, but would still leave the main jet fuel delivery steps too coarse.
Strange. This Powerjet circuit works wonderfully when tuned on the stock airboxed gsxr750 (and it’s pretty straightforward to tune on our EC997 Low Inertia Eddy Current dynamometers unlike simple inertia dynos.

The method of operation is as follows.
At full throttle, as the rpm increases, at exactly 10k, there is enough of a pressure differential between the float bowl and the airbox interior to draw fuel up the black hose on the LH side of the carb and exiting through the hole at the top of the bellmouth of the carb.
The fuel is metered by a jet that is located in the bottom of the float bowl. The jets are sized in increments of 2.5 or .025mm. Usual size for a gsxr750 with a stock airbox and air filter might be between #58 to #67.5.
The power jet circuit, when properly tuned, adds the equivalent of 2-3- main jet sizes “on top” of the main jet, so, if you were not using the power jet circuit, i.e. had a “0” or blanked jet installed with a #125 main jet, you would use a #117.5 with a #62.5 power jet installed.

Since this particular circuit works on the pressure difference between the float bowl and the airbox interior, it is absolutely affected by any change in the pressure differential. If the air filter is changed to less restrictive unit or the airbox inlet is modified, creating less restriction – the power jet area (size) should have to be increased above the usual size, though, a BMC or K&N, as installed for stock replacement, may only require 1-2 sizes increase in the power jet (in addition to +2-+3 on the main jet circuit).

If the airbox is removed, there is no longer a sufficient pressure differential to pull the fuel up the ~2.5″ vertical rise from the float bowl to the outlet in the bellmouth and the circuit is no longer effective.

Why is the Powerjet circuit difficult to tune on a simple inertia dyno and easy on our EC997 Low Inertia dynamometer? According to the former owner of Dynojet, the powerjet circuit simply doesn’t work because there is a lag in fuel delivery at 9.5k rpm – creating a flat spot there. It turns out that the reason that he saw that is that the dynojet dyno has insufficient load to simulate the Real World Loading ™ that is present on the bike in 4th and higher gears on the road or track. There is a slight delay in the onset of Powerjet fuel delivery, but it’s only vaguely present in second gear in the real world, and not present in higher gears due to the slower acceleration rate that occurs when you are actually riding. If you were racing, as Yoshimura USA and other non sponsored, large US Suzuki sponsored teams (we lent them carbs for the Finals) verified, the kit outperformed anything dynojet had to offer.

How to tune:
1. Install the main jet that produces the best power at full throttle / 8k-9k.
2. Install the powerjet set that produces the best power at full throttle / 10k to redline.
3. Raise or lower fuel level to get best power at full throttle / 3k.
4. Recheck main jet and needle height if you needed to lower the fuel appreciably.
5. Adjust fuel screws for best idle.
Note – this is the “short” tuning list!

Benefits:
The size of the main jet DOES affect the low and midrange. Excess leanness isn’t usually the problem on these carbs. Using a #117.5 vs. a #122.5 main jet (PJ equipped vs. using a #0 PJ ) leans and crispens the lowend and midrange for better off idle and corner exit performance.

There other applications on other motorcycles that use circuits that are called “power jet” circuits that work on different principles – some are electronically controlled and work in the midrange like RGV250, the RS250 for upper topend, where they activate and deactivate through different ranges and still others work for different reasons and by different principles.
“Power Jet” is a catchy sounding name and it gets used every few years or so…

Why did Suzuki specify that US and UK models, for example would have a blank or “0” jet installed, disabling the circuit and other countries, like Canada, got the activated power jet circuit (though with pretty odd settings)?
Emissions? I don’t think so. With the basic fuel level and needle settings virtually the same on both applications, using the larger main jet, as required with the circuit blanked, would only increase hydrocarbon emissions under measured conditions.

At any rate, the circuit works extremely well in dealing with the coarse main jet metering steps of the older style gsxr750 carbs – 1st through 5th place at the 1990 WERA Grand National Finals used our Factory Pro #CRB-S06-1.0 Carb Recalibration Kit. Pervasive kit use followed for the next couple of years -until 1992, the last year of the power jet.


 

Says it al really, but what I can’t figure out is why mine have size 0 jets fitted as my carbs came from the UK and so should have a functional circuit according to the article.
But anyway, as I am using separate K&N’s the powerjet circuit won’t be able to function properly so I removed the tubes and plugged the outlets inside the bellmouths.
This way you won’t have to disconnect the tube every time you want to change the main jets which can save you a lot of dyno time and therefore money. Now you only have two screws for the top cap and two for the float chamber which makes them very service friendly.

Thanks to Factory Pro for restoring my good night sleep!

Now that we are talking carburation technology I would like to point out two other things that are important.

When I remove the airbox and fitted separate K&N’s there were a few hose fittings that I didn’t know what to do with.bst38ss-4 In the middle of the bank of carbs there’s a 14mm big hole which acts as a breather for the float chambers. You need to connect a hose to this which is about 30 centimeters long to

A.) prevent dirt from entering the float chambers, maybe you’d even fit a small filter to the other and of the hose. A good and cheap trick is to nick some of your girlfriend’s nylons, put a piece of it at the end of the hose and keep it in place with a tie-rap.
B.) create a kind of buffer for the air pressure below the diaphragms. This is very important for the same reason you need to add tubes to the fittings of the float chamber breathers.

You need to connect a tube about 20 centimeters long to the fittings bst38ss-3of the float chamber breathers which are located between carbs 1&2 and 3&4. If you don’t do that the air pressure inside the float chambers will become very perceptive to pressure changes outside the carb like when you get some sudden sidewind or pass a big lorry.
I didn’t believe this at first until a dyno operator did a run before- and after fitting the hoses. The hoses made the powercurve much smoother and therefore made it easier to choose the right jetting.

Marc Salvisberg from Factory Pro Tuning says;

In the US, with a stock airbox, we didn’t have ANY problems with crosswinds, even 40-50mph gusting crosswinds at full lean at 100mph boogie. Actually, there is one problem – getting broadsided with a 50mph gust WILL push you off the track! Willow Springs in southern California. I thing that the biggest problem was the carb tuning as rides with our carburetion setups could: run with or without float bowl tubes, tuck their knee in of out, draft to the inside or outside of another rider while in a strong crosswind! It’s been a few years, but I definitely do remember the lack of problems with crosswinds. Urban myths started by someone in the States! Do the hoses affect the carburetion? Perhaps, to a very small effect. Less than running the bike again and increasing the crankcase temp 10F!

The only thing I can say is that we did a run with- and without the tubes installed and the effect was very clearly visible on the dyno graph. So when you fit separate K&N filters be sure to fit those hoses for the horses!

Thanks to Sandro Serafini, creator of Evo2 for the delicious carbs.