Introduction and hopefully a light build thread

[Whynotsooner]

G'day Guys and Gals

Just thought I'd introduce myself before drawing on your collective experience to the
to an excruciating level.

My name is BJ and I live in Queensland Australia, I am new to riding and working on bikes
However I have always had an unhealthy obsession of modifying and generally messing
with my cars, So hopefully with all your help I can further my hobby on a much cheaper scale.

Bought a yellow 04 GS with 16000ks on the clock (now 21000ks) as my first bike about 2 months ago
and love every minute of it, this website has been an incredible source of information for a new rider
and GS owner.

So far just maintenance on the bike, however I have just ordered a modest list of bits from the interwebs

Fork seals and dust covers
.90kg Racetech springs (I am a larger gentleman 6'2" 110kg)
04 katana 600 rear shock
Braided stainless front brake line
14 Ducati monster "flyscreen" (I couldn't get over the look of db-jte's bike)

I haven't decided on an instrument cluster, final colour, indicators.......or a lot of things yet
But I will try to keep you updated along the way with photo's and probably many many questions

All advice and input is welcome and will be taken into consideration.......not  necessarily adhered to.

[Watcher]

Welcome! 

Modding and riding motorcycles can definitely be cheaper than the same of 4 wheeled vehicles, but it's just as easy to go overboard and spend "too much".

No real advice yet unless you have any specific questions.

As always, pics or shens!  Word to the wise, the site no longer supports attaching photos.  You'll need to host on a site like imageshack or Photobucket.

[qcbaker]

...
As always, pics or shens!  Word to the wise, the site no longer supports attaching photos.  You'll need to host on a site like imageshack or Photobucket.

In case you aren't aware of how to post images on forums, OP, after uploading the image like Watcher says, you can post it here by doing typing something like this into the post:

Code Select Expand

[IMG]http://www.examplelink.com/photo.jpg[/IMG]

[ShowBizWolf]

Hi BJ! Glad to have ya here on the forum.

Congrats on the GS purchase. I like 'em in yellow    Can't wait to see what ya do. Good luck with your project!!

[Whynotsooner]

Will have to sort out a photobucket account, thanks for the heads up.

As for spending too much ''luckily'' the laws here restrict the type of modifications I am allowed to do during my first 2 years. Nothing that can be seen to add power

But surely I could argue that a k&n drop in filter was bought for the long term savings and I had to rejet it to sort out any idling issues.

[Watcher]

The K&N filters that drop in the air box aren't even visible, and neither is a rejet.  Are those even going to be issues?

[Whynotsooner]

Hopefully not. Nothing would really be an issue if I could guarantee never being in an accident.

Filter and rejet will be the most I can do performance wise without voiding insurance.

Better safe than sorry

[mr72]

But surely I could argue that a k&n drop in filter was bought for the long term savings and I had to rejet it to sort out any idling issues.

If you are talking about a K&N lunchbox filter, it's unlikely you will improve performance with it and required rejet. To realize any potential improvement would require a full exhaust and probably porting and maybe bigger valves, cams, more serious head work... There's just not like some unrealized power potential in the GS500 engine.

The downside is the K&N probably filters worse so you actually reduce long-term longevity with no potential for performance improvement. It does look better, though, and it certainly makes it easier to get the carbs on and off since the airbox is a giant pain. And it'll be louder with the lunchbox. If you are talking about a drop-in K&N it still filters worse than a paper filter but may not require as much of a rejet, doesn't improve performance either.

I have a set of pod-cone filters and jets sitting on my bench, where they will likely stay forever. I'll stick with the cheap paper filter, airbox, and my 40/127.5 jets.

[Watcher]

Aside from cams, valves, and other head work that actually mean good increases, an air filter and/or exhaust and a rejet is a simple way to gain some power output out of any engine.

It may not be much, but adding more air, adding more fuel, and expediting waste scavenging will cause an improvement.
We're not talking 20 horses, but especially considering the GS is tuned poorly from the factory you will have some gain.

Doing a head job without exhaust limits your increase, doing exhaust without a head job is a limited increase.  But saying it will do nothing is false.

Re: K&N filtering worse.  Higher flow means less restrictive element means it won't be as good as a paper filter at catching dust.
That being said, most K&Ns are oiled filters and people who make claims about their engines inhaling too much debris usually are the ones who didn't realise you have to maintain the filter...
A well cared for K&N is nearly as good as a paper filter but also has a higher flow rate.

[mr72]

Aside from cams, valves, and other head work that actually mean good increases, an air filter and/or exhaust and a rejet is a simple way to gain some power output out of any engine.

That's not always true.

If the air filter or exhaust are in fact the limiting factor, then they can improve performance. But provided the air filter and exhaust can flow the required maximum rate demanded by the engine, then there is no improvement available by increasing that flow rate.

Everything I have read indicates that in a GS500, the bottleneck is not the air filter or really the exhaust. Changing the exhaust from header to tip probably offers the most improvement (very small gain) but I'm pretty sure the stock air filter flows far more than the engine can consume without head work. Plus the stock air box has sort of an "velocity stack" in the throat that improves and smooths intake air velocity which you lose with the lunchbox, and the airbox itself kind of provides a large air plenum so the air pressure changes are equalized over a large area that may help improve power and transient response.

Far as I know, on a GS500 you have barely any gains to be made with full exhaust and no gains to be made with air filter. I would gladly replace my exhaust mostly because the stocker is ugly. And I considered putting pods or a lunchbox because the stock airbox is a PITA. When I had the top end rebuild done on my bike they did a little bit of porting just to improve flow (reduce turbulence) but there's no noticeable difference in power. I think it'd take an entire head swap as a starting point to get more power.

[Watcher]

The very nature of the fact you need to rejet means there's a power change.

A less restrictive filter and better flowing exhaust will cause your GS to run lean on the factory jets.  That's a fact.
More air going in needs more fuel, and more fuel means more combustion, and more combustion means more power.

The numbers won't be anywhere near what you get out of a cam or valves or a port and polish job, I know that.  I've actually done a head job on my GS, and subsequently had to go up in jets again from when I did my filter/exhaust, and by quite a larger margin.

At the same time, nobody is calling a K&N or a Vance&Hines a "high performance upgrade".  They aren't.

Maybe you won't be adding peak HP or peak torque, but as you said these simple mods can change the torque curve in relation to RPM.
If that means you reach peak torque sooner, or have a higher relative torque at a lower RPM, is that not a power increase?

[mr72]

The very nature of the fact you need to rejet means there's a power change.

No the fact that you need to rejet means there's an air velocity change.

More air going in needs more fuel, and more fuel means more combustion, and more combustion means more power.

You don't need bigger jets because of more air going in, you need bigger jets because slower air movement across the jet.

If it was actually using more fuel you'd get a huge drop in fuel economy by rejetting. With a lunchbox you might need 150 main jet to not run lean. That's a 50% larger (area) jet than stock. If you were actually burning 50% more fuel then you'd lose a third of your fuel economy, and unless there's a quirk with the efficiency of the GS engine you should also produce 50% more power. I mean, 50% more fuel, 50% more air, 50% more power, right? But since a 150 main jet and K&N lunchbox does not make a GS500 produce 70 hp that must mean it is not actually using more fuel.

It's using the same amount of fuel, just since the same volume of air takes more time to pass over the jet (lower velocity), the jet has to contribute more fuel per unit time, requiring it to be bigger.

That lower velocity probably also robs off-idle throttle response and transient response.

No point in arguing, but there are quite a few threads on this very forum that discuss in detail what it takes to get an extra 5 (10%) hp and it starts with an 8V head. Even trying to increase stroke and increasing compression or high lift cams and valve reliefs in the pistons doesn't get it done until you do something about the head.

[1018cc]

My 2c is to leave the jetting alone - leave things stock. Heaps of threads on here about flat spots and people not being able to get their bikes to run right after a rejet. If everything is set up correctly it will be fine and run right just as the factory intended.

If you've mucked with cars before then you might be right but when setting up carbs I think having a Colortune is the way to go to adjust idle mixtures (this is all you need if leaving the jetting stock) otherwise I reckon you'd need a portable wideband O2 sensor if you really want the bike to run correctly after a rejet. Take it from someone who has put a set of 98/99 ZX6R Kawa carbs on a 12R Hilux ute - I thought I had them running ok until I put the wideband on it but I was able to make heaps of improvements. Now idles at 13.5AFR, WOT gives 11.8-12.2 and cruise is 13.9-14.2:1. Too much of a guessing game without an O2 sensor. I thought my butt dyno was pretty good but now I realise it was way out of calibration! 

Are you in SE Qld? Good to see someone else from Qld on here.

[Watcher]

I'm not too proud to admit I'm wrong.  Most of my knowledge comes from my own experiences in the garage and the word of the "old timer".
No formal research.
But I do want to question a few things.

Doesn't make sense to me why a less restrictive air filter would cause a dip in air velocity.
If you had NO filter you'd be drawing as much as the cylinders can pull through the head, any filter at all would slow this down.
I know that exhaust can be tricky, as a suddenly larger diameter muffler which should be higher flow can actually slow the exhaust gas velocity and cause issues with scavenging, but on the intake side it's completely different since the flow of air is reversed.
A complex filter element should restrict the velocity and a less complex one should release it.


Also, I did notice a loss in fuel economy in my first GS after head work.
I had the valves recut and did a port and polish job.  On a K&N drop in and what was essentially a straight pipe I had to go with 145 mains to get it running right.
I went from around a 50 mpg bike to a 45 mpg bike.
Being primarily a commuter I was pretty well bound by traffic and the rules of the road, and less concerned with a smile as I was with getting to work and back safely, so I would argue as best as I could that I didn't change my riding behavior for my day to day (where I measure my fuel economy).


But of course your fuel cost goes up when your power increases, theres no physical way to change an engine's power output without spending more fuel.
Take a turbo, for example.  Forces air into the cylinder, but in order to keep proper AFR your injectors need to dump more fuel.
You get more power, but at the cost of fuel.

Any increase in air flow requires a percentile increase in fuel flow.

[1018cc]

I'm not getting into the whole air velocity thing as I don't know but the following is what I've noticed mucking with my ute (small 'truck' for those in 'Murica).

I have tried to tune the ZX6R carbs without the air filter and air box lid attached because it was less I had to remove if I had to make adjustments. I noticed on my wideband O2 that instead of pulling around 12:1AFRs at WOT, without the airbox lid and filter it would only pull 14:1 at WOT. It would back fire and be a real pig. After I reinstalled those two things the air/fuel ratios went back to what I expected. My conclusion is that on bikes everything is more finely tuned to work together so if you go changing one thing it will have an effect on everything else. Similar to having adjustable suspension on a car - adjust the height and that may effect your camber / castor etc.

[mr72]

I'm not too proud to admit I'm wrong.  Most of my knowledge comes from my own experiences in the garage and the word of the "old timer".
No formal research.
But I do want to question a few things.

Doesn't make sense to me why a less restrictive air filter would cause a dip in air velocity.

I agree, it doesn't make much sense. You have to get your head around how a constant-velocity carburetor works. Once it clicks how the carburetor is regulating air velocity, then I bet it'll make a lot more sense (it did with me).

It's because in the CV carburetor design, the volume of air coming in at any moment is limited by the position of the SLIDE not the throttle plate. When you open the throttle you create a difference in air pressure ("vacuum") between the engine side and the air-filter side of the throttle plate. That difference in air pressure is what moves the slide in order to allow more air in to the engine.

With a lower-restriction air filter you will have a larger air pressure difference so the slide moves further up. But the engine still demands the same amount of air over time, because it is simply an air pump displacing a certain amount of (mostly) air with each stroke of the piston at a given rpm. You can't demand more air unless you have more revs or you have larger displacement.

OK, so the volume of air over time at a given rpm is not changing, but the pressure of the air on the filter side of the carb is higher with a lower-restriction air filter, so the slide moves up higher, making a bigger opening for air to flow through the carburetor, and since the total volume over time has not changed then the rate at which that air is consumed must change. It's the classic water pipe example taught to explain the relationship of power, force and current.

Basically the "power" in this example has not changed (total volume of air/fuel consumed over time ... force x current) but the "current" has increased by opening the slide larger, therefore the velocity ("force") has to go down. For Ohm's Law that would be P = IE so if I increases then E has to go down by the same amount in order for P to remain the same.

It's all because the carburetor itself is governing the air velocity via the slide... it's a "constant-velocity" carburetor.

Lower air velocity, but more volume of air over the jet means the jet has to deliver more fuel in volume (at a lower total rate) to keep the AFR the same.

The reason you don't have to rejet the pilot jet when changing or removing the air filter is because the slide is closed. This only affects running on the main jet, when the slide is up and the needle is allowing fuel from the main jet.

So to make more power you have to either increase the air pressure above atmospheric, like with forced induction, so you effectively displace more total air and fuel (turbo, etc.), or you have to increase the compression ratio so you have more energy available for the given displacement, or you have to increase rpm. The limit in the GS engine is in total airflow (or displacement or compression ratio...) because the head/valves have a maximum rate they can flow so the engine cannot intake air beyond a certain rpm. So to really increase power you have to somehow make the engine consume more air over time, either by increasing the rate (rpm), the volume (displacement), or the compression (compression ratio or add a turbo/supercharger). Oh yeah and then figure out the fueling.

Mild head work like porting and polishing as was done with yours in the past and with mine recently will reduce turbulence and maybe make it flow a little bit more air but the real limit is the size of the valves, and then the mass of the valves after that (they can't open/close fast enough because of momentum). You could maybe put a higher lift cam and harder valve springs in and get a little more air in but there's a finite limit and a high-lift cam probably would require cutting valve reliefs into the pistons (I haven't looked) which will reduce compression ratio so you need a domed piston etc. etc. I went through all of this building my Miata engine (may she rest in pieces). There's a reason why bikes with a 15K redline make so much more power... they rev higher, and they can because they can handle the air flow rate (and myriad other things).

[Watcher]

Thanks for the lesson. 


Yeah, I 100% never even considered the operation of the CV slides.

[iamhiding]

heh... bjs are always welcome    haha looking forward to see where it all ends up no pun intended

also very good explanation mr72 

[Whynotsooner]

Hey guys and gals,

1st to 1018cc Yes, South east QLD.

2ndly The only "go fast" mods I was considering for this bike was the drop in filter, rejet and a 42 tooth rear Sprocket.

As you can probably see nothing radical here, 42 tooth rear is not quite as much as a 15 tooth front, just enough to hopefully get my fat arse up to speed a bit quicker
Chose to do the rear to minimalize the slight risk associated with going smaller in the front in regards to the chain meshing with the teeth.( Please see where I said SLIGHT). The filter and the rejet was only considered as eventually I will have to replace the filter anyway, and my understanding was the GS was tuned lean from factory.

The best way to achieve small gains on this bike (as with most vehicles) is to upkeep maintenance, clean and sync the carbs, set the valve clearance, eliminate vacuum leaks between carbs and head, have the correct tyre pressure, re-torque the head bolts on schedule blah blah blah.......Skip breakfast when going for a ride.

Also in regards to "performance filters" Having less ability to filter out particulates......well as long as you oil them often enough this doesn't seem to be an issue. I have run these style of filters on turbo cars (lots of damn airflow on a gt35/40) without seeing any damage to the turbo blades over the course of years (even if I was a bit lax on the oiling)

3rdly  I'm still waiting for my damn parts,  Will post up some pictures before I mess with it and after.