Bike of the Month August 2017

Bandits, they crop up for discussion from time to time on OSS. Are they interesting? Are they not? They get referred to as ‘blandits’ unless they’re decent and have always been seen as a good source of parts, particularly the engine for our beloved OSS bikes.

So, when we set about rebooting OSS into what it is today we had a think about how to word which bandits we’d like to see on here… specifically no blandits! However that needed a tad more definition so we ended up with the following as part of the rules: “Standard bandits just aren’t that interesting. Trick ones are another thing though, there are indeed some out there and we’re not talking bolt-on tat. GSXR running gear, 1216, flatslides, turbos etc, that makes them interesting!”

When it was time to choose this month’s BOTM, I saw Colinworth79’s Bandit Evo thread and re-read that definition. My thought was that maybe it’s time for a ‘non-blandit bandit that’s still somehow a bandit’ BOTM. I also like well-executed tasteful trick details and I like shiny… so here we are.

Trick frame? Tick. Upgraded running gear? Tick. Turbo? Fucking tick! There are so many upgrades and details on this bike. GIA frame (11kgs lighter than the stock), Ohlins suspension, Harris/custom yokes, that swingarm, lightweight wheels, big bore, turbo, the list goes on with some amazing details and one-off parts along the way. Recognisable as a bandit however very trick and lacking in renthal bars and twin dominator headlights too!

The bike has competed at the Brighton Speed Trials and has since been seriously crashed and rebuilt along with further upgrades. It doesn’t stop there though, a 1340 motor is now being prepared for it too.

So, here we have it – we’ve got a bandit as BOTM. Yet it’s not a blandit. It’s the opposite of bland yet it’s still got the recognisable silhouette of a bandit. Is it still a bandit? Who cares, it’s our BOTM.

Colinworth79, your Bandit Evo is this months BOTM.

Read the project thread here.

Discuss this article here.

If it ain’t broke, it doesn’t have enough power yet – The quest for speed.

This year we’ve had the pleasure of following one of our youngest members on his crusade to build a winning 300bhp turbo wheelie bike based on a GSXR1100 Slingshot from the 1990’s. We all watched in amazement as the master plan took shape and we rode the roller coaster with him throughout the year.His determination and focus was such that  it soon became clear he was either going to break a record, break his engine or break himself.

Fortunately he managed the first 2 and not the 3rd. Here’s Kev Kearsley’s round up of  his 2016 campaign. He went into this  year as the Kid Kearsley but nobody can deny that he came out the the other side Da Man!

The Quest for Speed

Kev Kearsley

Ever wake up and think I’m going to do 200mph today? Tuesday was one of those days.

The Top Speed Tuesday put on by Straightliners at Elvington marked the last event of the year for myself, and what a year.

With numerous top speed days for tuning the bike for the Wheelie Comp, seeing a failed 194mph kilometre wheelie for dropping it a few metres short of the required distance.

A trip to Pendine sands in South Wales where I set two land speed records reaching 174mph on sand.

Hundreds of miles on the road two up

A track day at Oulton Park in the soaking wet, 300bhp on summer race tyres in the wet is not advisable Kid.

A few static displays at various motorcycle shows to fly the OSS banner including Donnington where my alter ego Rene took the old girl for a few laps of the track.

Many visits to RTR motorcycles for dyno runs, one off which was for the OSS dyno day where the bike made 300bhp.

So all in all a good year! Just think of the stress that engine has had doing all that, the only fault I got all year really was a leaky block so I’d say quite a reliable one.

Lets go out with a bang! I had that shit or bust attitude on.

It had been raining all Monday night making it look like the event would be cancelled, that gut wrenching feeling driving to the track in the rain for 2 hours thinking this ain’t gunna happen today. The rain stopped thankfully and after waiting a few hours to allow the track to dry we were given the all clear to attack the track.

The bike is, as a few of you know, made for wheelies, this means a short 55″ wheel base and big horsepower, not an ideal combo for Land Speed Racing.

Time to do the job. I was waved off by the starting Marshall after sat staring down a 3km runway. Short shifting 1st, 2nd, 3rd into 4th with a little wheel spin as the track was cold and still damp, into top gear and the bike is now naturally wanting to wheelie up in the air, feathering the throttle on and off to try keep the front wheel planted was an impossible task.

kk-speed-1I felt gravity some what take over just shy of the line and I managed to pin the the throttle open all tucked in with my chin on the tank as I had no fairing to hide behind.

kk-speed

Made it. Still alive. Slowly throttle off as not to upset the bike, heart beating, did it do 200?? That drive back to the pits and the timing office seems to take forever.

203.8mph! On an unfaired 30 year old motorcycle with a well and truly abused engine.

kk-times

Thank you to all involved over the past year for parts, advise and food.

Use the link below to view the onboard action.

https://drive.google.com/file/d/0B0QcmiqJi-rISzdsMzdYTkJscU0/view

 

Setting up CV carbs for a turbo

See below all I know about blowthrough CV carbs. This is worth several hundred hours of sorting out and at least €1000,- worth of dyno time, so feel free to thank me! (and/or make a paypal donation)

Bowl pressure
If pressure in venturi of carbs is raising due to boost, so should the pressure in bowl raise. Because if pressure in bowls is lower as it is in venturi, no fuel can be taken into the engine.
In my experience dynamic boost is absolutely nessecary, and it’s best to give each connection on the carbs it’s own spot on the tube going to the plenum: not in the plenum itself as there is to much pulsing. Make sure they are “angelcut” and in the middle of the airstream. (also known as pitot tubes)

On the GSXR1100 model 92 with the 40mm carbs you need to fasten the rubber T’s for instance with steel wire to prevent leakage and pressure drop.

Membrane pressure (CV carbs only)
Pressure above slidemembrane is not needed: it got it’s signal/pressure through the hole in the slide. Don’t enlarge the holes because the slides go up too fast and cause stuttering. (beware of dynojet kit modifications: larger holes and softer springs are a real pain in the butt for the midrange!)

Pressure below the membrane is needed. On the GSXR1100 model 92 with the 40mm carbs you have a seperate “venting” system with external hoses. Those are not suitable to pressurize. I removed that system, plugged the holes and drilled holes from the bellmouth towards under the diafram. When you drill you cross a not used hole. You have to plug that up also to prevent leakage and pressure drop. So it is made like the earlier models: the 36 and 38 mm CV carbs do not have this system.

Fuel pressure
The pressure of the fuel going to the bowls should be higher than the pressure in the bowl. If not, not any fuel is flowing into the carbs causing starvation as soon as boost starts to build.
Therefore you need a pump capable of making enough pressure to overcome boost + 2-3 psi at sufficient amount of fuel. The standard membrane pump on some carb bikes is definitely not up to the job: don’t even try it. An automotive EFI pump coming out of a car with the same amount of horsepower you are aiming for should work allright.

If you don’t use a regulator: you will have the maximum pressure on the bowls the pump can handle, and that will be around 90 psi and the end of your carbs.
A regulator is used (I use a malpassi and highly recommend it) to give the carbs a 2-3 psi above boost, so difference in pressure between pump and carbs is always the same independent of boost. Make sure you use a bypass type, not a deadend type as it is less accurate. If you can get away with 5 psi on the carbs without leaking, you can use static pressure and don’t need to modify the malpassi. It you have trouble with it, as I have, you need to shorten the spring in the malpassi a bit to achieve 2-3 psi. I also needed a bigger 8mm return line to be less restrictive. Than you definately need the dynamic pressure to prevent starvation under boost!

Jetting+tuning
Don’t make holes in the slides bigger, or use soft dynojet springs! They make things worse in the midrange area.
If you have your carbs and fuelsupply correctly setup: you don’t need to make big adjustments to needles and jets. Mine is actually on 125 mainjets (stock!) functioning just fine at 11.5:1 A/F
Don’t get an A/F any leaner then 12:1 A/F when you use some serious boost. You will burn up some pistons/valves. 11.5:1 is safe imho.
Use an A/F meter to see what’s going on. Looking at plugs is not saying too much, because if their getting hotter then normal on a turbocharged motorcycle they are white anyway.
Symptoms of lean and rich while driving can sometimes be very similar so in doubt always consult the A/F on a dyno!
Because of the lowered fuellevel it is nessecary to give more fuel for the idle, in my case 8 complete turns out for the mixture screws.

Extra tips:
Place a fuelfilter between pump and regulator. Not before pump because you restrict too much, and not after regulator because you messing with pressure which is critical on a carb/turbo setup. Make sure the fuelfilter can hold the pressure!
The return line of the regulator should be as less restrictive as possible: inside minimum 6mm returning into TOP of tank, not below fuellevel in tank. Otherwise fuel pressure cannot go as low as 2-3 psi. Don’t ever (I mean ever!) bend this line because fuel pressure can reach scary levels damaging your carbs seriously!!!!
Mount a fuelpressure gauge direcly next to the boost gauge so you can easy troubleshoot. Remove later if you want to.
Remove filter in your petcock, or better mount a less restrictive petcock without filter. Pingel makes these, but I machined a custom one with build in fuelreturn to the top of the tank so you don’t have to weld in a separate fitting in the tank
If it’s a vacuum operated petcock make sure you use the bypass mode: otherwise on boost the petcock will shut! This is a nice one, as you easily overlook it. On some models the petcock is really restricted in bypass mode so you have to modify that in some way.
If carbs overflow: put in new needles and valves. Make sure fuellevel is not too high: pressurized bowls have a slightly higher fuellevel so you maybe have to adjust it a few milimeters.
On very high horsepowerlevels there can’t flow enough fuel past the needles. Put in thinner/sharper dynojetneedles to solve this. Typical symptom is a sharp leaning out around peak torque, were you need the most fuel every stroke. This makes it harder to get the midrange ok.
At higher boost you can press out the choke plungers! This causes unwanted rich situations and stalling at closing the throttle. Put in stronger springs to solve.

Disclaimer
This info is true for my bike and my application. Some of this info is also true on other bikes/carbs but you have to check yourself. If it doesn’t work or you burn your engine up: I don’t accept any claims. If you crash due to an exploding engine: I’m really sorry and I will send flowers to your family but I am not responsible!

Good luck!

>> Check out the hints section of www.turbo-bike.com, site has an illustrated guide for “converting” CV’s for turbo use.
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The small 34mm gsxr750 carbs with alloy throttles and 4 screws on the caps and floats are actually the best you can use when going turbo. A friend (at is cranking out 420 rwhp at 2.2 Bar of boost.
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I’m also using 34mm carbs on my turbo GSX with alu caps. One more tip: Replace the o-rings in the T-s that go to the floatbowls; 9 times out of 10 they are old and brittle and will leak your precious dynamic boost so the motor runs like a pig at the transit from vaccuum to boost.
One important thing that I noticed during dyno-testing is that you (usually) start with std. mains, then lean it out a bit. If you go down-or upsize the mains, they have a bigger effect on fuelling than it would on an NA engine. So where you would normally say take it 3 sizes down at a time, you need to take one size at at time with this setup.

Marco.

for 38-40 mm carbs

vergaserdeckel-deckel

vergaserdeckel-gsx-r

http://www.gsg-mototechnik.de/