cutting fork springs + pod filters

So, I recently purchased a 91 EX500. Since then I have spent time reading ex-500.com

Either I didn't pay enough attention in Physics class, or the people on that site are totally off their rocker.

FOG said: The 1st gen bikes enjoy a really long spring 22" if I remember right. This give a lot of room to experiment with diffrent cutting a shimming. For almost free you can tune your forks to suit to perfectly. As you cut (shorten) the spring it's rate(see glossary) goes up. For most riders over 150 lbs the springs are too soft. start but cutting about 5" off the spring legnth then replacing that legnth with a piece of 1" PVC pipe cut to a legnth that will support the sag at about 1 1/4" Note you may have to cut several spacers to achieve this , but 10 Feet of PVC is only about 3 bucks at Home De Poo. If that legnth is too soft you can cut more and re shim etc. AT My home racetrack there were two places that the forks bottomed out even after I got the ride I wanted everywhere else. The controll This I added another short set of springs down inside of the main spring. I used 2 of the innere valve springs in each fork. These springs were operated by a Legnth of 1/2" PVC pipe inside of the 1" cut to a legnth that would just cause them. to come into play near the bottom of fork travel. Thereby adding there rate to the main spring and stiffening the whole thing to prevent bottoming with out making the normal ride too stiff. BTW this is what the Race Tech Emulators do for 130 bucks or more Spring rate: is the force required to compress a spring a given amount. straight springs like this are uniform. that's is exactly the same increment will colapse the spring the same amount till the coils are solid. Explanation: if 10 lbs collapses the spring 1" every 10 pounds thereafter will close it another inch, 30 lbs+3" Have fun and don't be affraid to cut the spring. FOG

I'm pretty sure that if you have a 100 lb/in spring that is 2 feet long, if you cut it in half, it will still be a 100 lb/in rate spring. The idea of cutting a spring and replacing it with a PVC pipe seems totally... pointless. You would lose total available spring compressionage (yes that is a word) while not changing the spring rate.

Issue number two. This man "FOG" who is hailed as a god on this forum also came up with an idea that pod filters don't make more power. He says that the 498cc engine pulls 498cc worth of air no matter what, and that changing the filter will not increase power output... that instead it just makes the bike run more lean. He states that the lowered pressure in the carb will draw less fuel.

My take: If you have a more free flowing intake filter the pressure drop over the intake filter will be lower. Yes there will still be only ~500cc of air being gulped, but since the pressure in the cylinders is higher, the total available oxygen molecules is higher which results in more power potential.

While it does make sense that you would 'draw less fuel' due to the lower pressure in the carb, this is why most people go to a larger sized jet.

Why does Hooke's Law or the Ideal Gas Law not apply to EX500s?

Am I wrong?

I think stuffing 5" of pvc into the fork and further compressing the entire spring should achieve the desired result.. am I correct?

Carbs and I dont get along. Im useless there.

In reply to 4cylndrfury:

I thought about that, but he's talking about removing 5" of spring and adding 5" of pvc pipe. .....

Taiden wrote: In reply to 4cylndrfury: he's talking about removing 5" of spring and adding 5" of pvc pipe. .....

= same spring rate w/less travel

or

= fail

If you cut down a spring it becomes stiffer. He is saying you take the 22" free length spring that has say a 100lb rate, cut it down to a 17" spring that would have a higher spring rate. A spring is just a torsion rod rolled into a coil. If you have a 10ft long piece of pipe and a 5 ft long piece of pipe, the 5 footer will be much harder to twist than the 10ft (assuming the same construction). Since the bike weights the same and you have a shorter spring, you need to shim out the perch on the fork to provide the same ride height/sag as the origional spring. He doesn't say how much to use, but advises you to try different lengths. Basically the PVC pipe acts like a adjustable perch on a coilover. I think his solution to the bottoming out problem is Genius. Simple effective and CHEAP! PVC pipe is pretty stout in compression especially when contained so it can't buckle. Sure the little springs are hopelessly stiff, but they have softer spring rate than the INFINITY that bottoming out the fork does.

The rate of the spring material stays the same, but number of coils is part of the spring rate equation. Remove coils, and the spring gets stiffer. If the filters make it run leaner, then how is it doing so without flowing more air? More air = more power.

I own an ex-500, the only mod I recommend is FOGs airbox and pilot screw mod. immense difference in low-end power

Grtechguy wrote: I own an ex-500, the only mod I recommend is FOGs airbox and pilot screw mod. immense difference in low-end power

I guess I should outline this for people not on the forums.

FOG has people drill a 1" hole in the stock airbox + turn out the pilot screws more than stock (I believe 2.5 from the bottom).

He also says to NOT use pod filters and rejet.

I cannot figure out why anyone would say this. If you put pod filters on a bike you should be able to get it to a decent AFR by rejetting it. Free flowing intake = more oxygen in the cylidner = more power.

Of course, I would bring these points up on ex-500.com... but these exact same points have been brought up and people just blindly follow FOG.

As for the spring thing... I just looked up a spring rate calculator and found that yes... it is true that when you cut the springs the rate increases. That seems weird to me, but now I see how it works. There are less coils to give way to force, so the spring will give less which is a result of a higher spring rate.

If you read the ex-500 site some more you will find that the carbs are venturi style.

the airbox provides a smoother air delivery than pods, thus cleaner/smoother acceleration.

He's not saying you can't use them, but they will be of zero if not negative value

Grtechguy wrote: If you read the ex-500 site some more you will find that the carbs are venturi style. the airbox provides a smoother air delivery than pods, thus cleaner/smoother acceleration. He's not saying you can't use them, but they will be of zero if not negative value

I definitely don't know much about carbs, but I thought they were standard CV type carbs which I thought lots of people in the Cafe 'scene' put pod filters on.

Maybe that's just aesthetics.

Either way, I'm glad I asked. I understand things much better now.

Grtechguy: how many turns out did you go on the pilot screws? How significant was the difference?

The spring rate part is correct.

The pod filter part is incorrect, but on my ex250 the only real benefit was that it sounded tougher.

I set mine to zero, then 2.5 out.

Wow, what a whacko. The spring rate part is correct, if you shorten the spring you will increase spring rate. Picture the spring straightened out. if it's shorter, it will be harder to bend. And the fork only has about 5" of travel. So replacing the lost length of spring with pvc (ie a preload spacer) is not going to limit the travel of the fork. Just adding a longer preload spacer, will not increase spring rate, it will just increase the initial force required to move the wheel. so that will not give you what you want. It would make the bike not absorb small bumps very well, but will not do anything to keep the bike from bottoming under braking.

The short springs he is adding is nothing like the race tech emulator. The emulator affects damping, increases low speed compression (control brake dive) and acts like a relief valve allowing you to tune high speed compression (bumps). So more low speed damping will slow down dive under braking everywhere in the stroke, not just at the end. He is trying to create a progressive spring, which no real racer would use.

If the fork works well everywhere else, and bottoms in a couple of spots on the track, you can add fork oil (ie decrease the air gap)

He is correct about the pods, modern bikes have tuned airboxes.

Wow, I just spent a few minutes on that site. pictures of guys working on the forks still on the bike using gearpullers, drilling holes in the forks for "drain plugs", people wanting progressive springs, etc, makes my head hurt. lots of bad advice on there.

Danny, after spending time on Thumpertalk and ADVrider I was starting to come to that conclusion. I think I'm going to stick to my guns from what I have read on other sites. I'm sure there is some good info floating around there, but other stuff is just scary.

Here's another one: FOG says that if you drop your bike, to 'burp' the oil system you should unscrew your oil filter until it starts to drip a little bit of oil... then CRANK the bike until oil spurts out around the filter. This is supposed to "remove trapped air" from the oil system.

I'm no expert on motorcycle oiling systems... but any bubbles caused by a bike tipping over (if they would happen in the first place is another thing) would rise to the surface in the gearbox/oilpan and disappear. It's not like they would be 'stuck' around the oil pump or anything.

oil pumps are positive displacement anyway, sothey are self priming. If you're worried about air, just crank it with the ignition off until the light goes away, the same as starting a dry engine.

danny_never wrote: He is correct about the pods, modern bikes have tuned airboxes.

No offense to any owners or aficionados, but EX500s are hardly 'modern' engines.

I have a very hard time believing they wouldn't benefit from freer breathing and an appropriate rejet.

"modern" or not, it still has an airbox. "benefit" by making more peak horsepower? maybe. run stronger throughout the rev range. not likely. especially being tuned by guys without a dyno.

burping the oil system? never heard of that one

Irrespective of the maths to determine what that does to rate - it's ghetto. And so are pod filters on any motorcycle made after 1985.

Buy a set of Progressive Suspension or Racetec springs, some oil and or a set of emulators and be done. bear in mind if you don't do something about the miserable excuse for a shock absorber the bike ships with that once you've got the fork working the shock will seem even worse.

Fortunately there's plenty of ex-race EX500 stuff out there (start w/ the WERA forums classifieds) from guys who now race SV650s. Or worse.

As for pods, a K&N filter and Dynojet kit is considered a necessary part for any carbureted motorcycle. If it has an airbox, remove the snorkel or hole-saw a little more aperture in.

Pods look good on a KZ900 or an '83 GS1100E. Maybe even a first or second gen GSXR750 or 1100 "oil boiler'.

I had 'em on my FZ600 road racer 'cause it allowed the carbs to come off alot faster, but on the dyno it was a wash w/ the airbox.

IMO, an a bike like an EX500, there is no reason to start modifying the stock forks. There are lots of Kawi's out there that came with MUCH better forks stock, just swap them. IDK Kawi's well, but I know Honda ran the same steering stem critical dimensions for the better part of 30 years. Pick up some some ZX6r forks and you will get full adjustability and stiffer/larger tubes, as well as better brakes and a lighter wheel, possibly for around the same cost as springs and emulators.

I've been thinking about some cbr600f3 forks for my '75 CB360, they bolt on.

Adding pods and doubling the size of my main jets improved overall ridability as well as mid and high end performance.but that's on a 1986 rg500 two stroke