A Caution on Performance Mods (My Experience)

[Easy Rider]

Set up:
2006 GZ 250 with 16T front sprocket, US/Canada model (non-California)

There is a lot of information already on here about intake/exhaust/carb mods. Most of it is good but some is just plain misleading (dare I say WRONG). :roll:

So here's my take:

Don't undertake ANY air box mods or any drastic exhaust mods unless and until you are also ready to do the necessary carb mods too.

If you want to see what a less restrictive intake will do for you, just take the stock air filter OUT and ride the bike for a half mile or so. (This will NOT hurt anything unless you do it on a day there is a dust storm or you ride on a dirt road!). It makes a big difference alright; it runs like crap! Do NOT do this in traffic; you are likely to get rear-ended!

So, after that little test, I put my air box back to stock; runs good again. I even put the diverter back on in the stock position 'cause I could tell no difference with it off, on or turned around. In the stock (facing to the rear) position it offers protection from sucking in rain and large particles.

On to the exhaust. I drilled 4 each, 1/4 inch holes around the outlet INSIDE of the ridge that forms a ring on the back plate. Others have done it outside of the ring and I wanted to try something different. That plate is HARD; drilling where I did goes through 2 layers of metal. I'm assuming the inside layer is the end of the baffle "can".

The result was generally good. The sound is a tiny bit louder but I doubt anybody but the rider would know the difference. The note is a little bit deeper at low speed. Wind and engine noise still pretty much masks the exhaust at higher speeds so I can't tell if it is louder or not. I did notice (I think) a slightly different sound from the top end of the engine after the new holes. Not necessarily louder than before, just different. I am not concerned with this as it was (somewhat) expected.

Is there any difference in performance? Not much if any. I think I've got slightly better acceleration and a tiny bit more at the top end but the difference is so small that it might be all in my head. I plan to leave it this way. Riding more than my initial short test may give me a better perspective on this.

NOTES: Since non-US/Canada models are jetted differently when stock, the results on those bikes would probably be different.

I did notice in my short test that under some conditions (head wind, up a long hill, etc) I am now able to go faster in 4th than 5th gear (with 16T front sprocket). I shifted at ~ 63 mph in 4th but I think there was some left. In 5th, it strained to maintain 65. On the return trip (with the wind), I approached 75 with no problem before it flat-spotted.

More later but I think I'm done........at least until I see the write up on the latest carb. mods.

Feel free to add your experiences with "simple" mods but discussion of the carb/jetting part probably should be put in threads specific to that.

[Badbob]

In my opinion messing with the air flow on this bike is waisting time and money.

If someone wants a bike that goes faster It would have been better to buy one that goes faster.

[jonathan180iq]

Originally Posted by Badbob

In my opinion messing with the air flow on this bike is waisting time and money.

If someone wants a bike that goes faster It would have been better to buy one that goes faster.

We'll see. It would be better to have real information based on experience, than to just say "We'll, I have never ridden a GZ with a different intake set-up and jetted carbs, but I don't think it's worth it."

It may turn out that you are right. However, no one has done it, so I want to know. If I am wrong, I'll probably be the first to mention it.

Also, have you ever ridden a bike with a 16T front sprocket? If so, you'd know that, while the gearing is perfect for just about any other type of riding, top speed is limited to 65-70MPH. Opening up even a small amount of juice on the top end, which is what you get from a free-flowing intake, should result in a small increase in top speed. (interstate/open road riding)

Also, when you say "time and money" I know you don't mean a few hours and $30 at max. Anyone who is serious about getting the work done doesn't need to spend much more than that.

[jonathan180iq]

Originally Posted by Easy Rider

Don't undertake ANY air box mods or any drastic exhaust mods unless and until you are also ready to do the necessary carb mods too.

If you want to see what a less restrictive intake will do for you, just take the stock air filter OUT and ride the bike for a half mile or so. (This will NOT hurt anything unless you do it on a day there is a dust storm or you ride on a dirt road!). It makes a big difference alright; it runs like crap! Do NOT do this in traffic; you are likely to get rear-ended!

I had the crankcase vent hose slip off of my air box the other day. First of all, I noticed a very deep intake tone and I kept saying to myself, "Man, self. Whatever that is sounds awesome". Then, upon realizing that I couln't go much faster than 50 miles per hour, I discovered the hose.

Now, anyone who has looked down there knows that the opening left from that hose detached from the bike is only as wide as a woman's pinky. Even this sized hole made a significant difference in the function of the bike. The reason for this loss in performance? LEAN air/fuel ratio.

The reason that Easy and I experienced the same thing is because there is no longer enough fuel in the combustion chamber to make a significant boom when coupled with SO much air. And a lack of significant boom results in not enough power on the down stroke to drive the bike. Couple this with the fact that giving it more throttle, while allowing more fuel to flow, also increases the amount of air being sucked in and you can see the dilemma.


This is probably the most important lesson of the day:

Don't undertake ANY air box mods or any drastic exhaust mods unless and until you are also ready to do the necessary carb mods too.

[johncruise]

Again, I'm not a knowledgeable person in terms of motorcycle mechanics but I have to ask this anyway since I'm planning to change my muffler...

1) by exhaust mods, that includes changing the muffler? (not just punching holes--- changing the muffler like that EMGO turnout muffler)

2) with the lean air/fuel ratio problem -- can we fix that by using a different octane gas for faster burning and or messing with the idle screw below the tank.

(please bear with me with my questions)

Thanks!

[jonathan180iq]

Essentially, by swapping mufflers, you are installing what are called "slip-ons". Generally, with slip-ons, a re-jet is not required but it is recommended. You can probably get away with just raising the needle on the carb.

You will be increasing the efficiency of the bike to push out spent combustion gases. A vaccum is created, with the down stroke, to pull the next batch of air and gas into the cumbustion chamber for the next explosion. Leaning this mixture has the same effect as increasing the air flow from the other side, via an intake mod.

Now, it should be noted that on most bikes of this size, the exhaust is not as restrictive as the intake. So, exhaust mods which do not increase the header capacity have little affect on the air/fuel ratio and therefore don't usually require the bike to be rejetted.

If a performance exhaust was available for this bike and you were installing that, then you would most definately be required to rejet for proper performance.

Unless the bike acts funny after you change mufflers, you'll be fine. I would suggest that you at least raise the needle one notch, to help in the midrange of the bike and counteract any slight leaning that the EMGO muffler may induce.

Good luck,
Jonathan

[johncruise]

That was a very sound advice and very informative. Thanks Jonathan!

[Easy Rider]

Originally Posted by jonathan180iq

Not with the stock US jetting you won't. That was, after all, my main reason for starting this seperate thread!

[Easy Rider]

Originally Posted by johncruise

1) by exhaust mods, that includes changing the muffler? (not just punching holes--- changing the muffler like that EMGO turnout muffler)

2) with the lean air/fuel ratio problem -- can we fix that by using a different octane gas for faster burning and or messing with the idle screw below the tank.

Better to ask BEFORE than to say "What happened?" after! :roll:

Good answer from J.

To add just a bit:
If you are installing a "real" muffler, you will probably be OK. Before you put it on, hold one end toward a light bulb (turned ON, of course) and look in the other end. If the hole looks black (no light coming through), you should be OK. If you can see a hint of light coming through, you might need carb adjustments; might not either. If you can actually SEE the light bulb, meaning there are no baffles and it is not really a muffler, then it is likely you will need a carb adjustment (and IMHO, you probably won't like the sound either!).

If you are going to have to do any welding or cutting to fit the new ones on, you should consider the possible effect carefully because going back can be difficult and expensive.

The octane rating of gas does NOT have any significant impact on the mixture.

Good luck!

[jonathan180iq]

Originally Posted by Easy Rider

I was hoping that was implied.