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! :cry: 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.
:tup:

[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]

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]

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! :cry: 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]

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)


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

[Easy Rider]

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! :tup:

[jonathan180iq]

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)


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

I was hoping that was implied.

[Badbob]

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.

Perhaps this is cheap if you have nothing better to do with your time than work on your bike. I'd rather be riding than spending a Saturday afternoon modifying my bike so it will go 2 mph faster on a good day. For me the cost is way to high and the benefit is minimal. Most of the places I ride a 2 mph increase in top end is of no use what so ever. I have a bike that will go way over 100 mph if I want to go that fast. Thus for me its a waste of time and money.

[jonathan180iq]

I have a bike that will go way over 100 mph if I want to go that fast. Thus for me its a waste of time and money.

I don't.

[Badbob]

I have a bike that will go way over 100 mph if I want to go that fast. Thus for me its a waste of time and money.

I don't.

And you GZ250 never will unless you spend enough time money on it to buy one that will. In which case it will not be GZ250 any more.

[jonathan180iq]

going a set speed on the speedometer is not the goal. going 100mph is not the goal. The goal is to add, if possible, a little more kick on top for passing in top gear. Like I've said, you've not experienced the lag of a 16T sprocket in 5th wide open. That's all.

[Badbob]

going a set speed on the speedometer is not the goal. going 100mph is not the goal. The goal is to add, if possible, a little more kick on top for passing in top gear. Like I've said, you've not experienced the lag of a 16T sprocket in 5th wide open. That's all.

Key word here being little. More likely tiny.

[Gadzooks Mike]

What I've found with the 16T sprocket is not any higher speed, but a much better gear ratio. It makes riding a lot more comfortable.

[jonathan180iq]

You're right.

It was kind of frustrating on the ride down to Franklin. My daily route never requires much more 50-55mph here, in town. That being the case, I have suggested that every single person switch over to the 16T sprocket. Now, however, as I have spent a good deal of time on the open road where high speed would have been nice, I'd suggest that, on long trips, the 15T be used.

I simply could not go any faster than 60-65mph at any point on our trip. At one point, I got behind a Semi and drafter him for maybe 15 seconds and that really helped.

However, Mauricio, with his 15T could blow right past me in 5th. (The 16T is actually faster off the line up to maybe 50mph.)
It seems that the internal gearing for 5th gear is just so big that the added gearing provided by the 16T sprocket is too much for the bike. In gears 1-4, this gearing is just about perfect. 5th gear is perfect for around-town riding. However, on major highways or if you want to sustain 70mph for a long period of time, 15T is the way to go.

[Easy Rider]

Key word here being little. More likely tiny.

Enough, already. Is this just an OPINION you have formed by listening to others OR is something you know based on personal experience ??

Either way, I think you've made your point. :mad:

Chill!! :tup:

[Badbob]

You're right.

It was kind of frustrating on the ride down to Franklin. My daily route never requires much more 50-55mph here, in town. That being the case, I have suggested that every single person switch over to the 16T sprocket. Now, however, as I have spent a good deal of time on the open road where high speed would have been nice, I'd suggest that, on long trips, the 15T be used.

I simply could not go any faster than 60-65mph at any point on our trip. At one point, I got behind a Semi and drafter him for maybe 15 seconds and that really helped.

However, Mauricio, with his 15T could blow right past me in 5th. (The 16T is actually faster off the line up to maybe 50mph.)
It seems that the internal gearing for 5th gear is just so big that the added gearing provided by the 16T sprocket is too much for the bike. In gears 1-4, this gearing is just about perfect. 5th gear is perfect for around-town riding. However, on major highways or if you want to sustain 70mph for a long period of time, 15T is the way to go.

I see what your getting at. The 16T front sprocket trade off takes away some of your performance. Acceleration is some what less but you get a little smoother operation and better use of lower gears at lower speeds. If I have this right you are not completely happy with either the 15T or 16T. I just ordered new front/rear sprockets and a new chain. I got a 16T front sprocket now I'm thinking I should have ordered a 15T as well just in case I don't like it.

I don't know if switching sprockets back is a good idea. According to al the al the experts I can find you should not use a new chain on old sprockets or a new sprockets on an old chain. As I understand it when new the chain and sprockets are machined to fit. As they wear togehter the fit stays pretty constant. If one or the other is changed for a new one they no longer fit and wear is accelerated. I've never seen any discussion on what happens if you change sprockets on a regular basis.

Have you considered running in 4th gear instead of 5th at highway speeds? I have done this for considerable distances. I once rode about 120 miles at 60-65 mph into a strong head wind in fourth gear. I could not maintain 50-55 mph in 5th gear. 5th gear is essentially over drive. I have read some good discussion on the 4th vs 5th gear issue on other forums. As I remember there is a good bit of it on 260nija.com. What I got from this is that 4th is for acceleration, climbing hills, etc and 5th is for cruising and economy, You might want to consider using 4th gear in those situations. This is what I had planed to do after the 16T sprocket is installed. I'm going to find out how it works for me, I expect it will be fine in Tallahassee but I might have problems in hilly country. Although mike didn't seem to have a problem with his on our Franklin trip. Actually this is the primary rason I decided to try it.

I don't want to ride anywhere that I need to maintain 70 mph. I would not mind being able to go that fast easily just don't want to.

[Easy Rider]

[I don't want to ride anywhere that I need to maintain 70 mph. I would not mind being able to go that fast easily just don't want to.

IMHO, you are a perfect candidate for the 16T. The above is all you lose and I think you gain a lot. Since you already have experience "cruising" in 4th, it should work even better.
I figure if I HAVE to get somewhere in a hurry, such that I NEED to use the Interstates, I will be in my car and not on the bike.

While your information on chain/sprocket wear is correct, you should be able to do a hundred miles or so with the 16T for a test and still go back to 15 with no ill effects.

[Badbob]

[I don't want to ride anywhere that I need to maintain 70 mph. I would not mind being able to go that fast easily just don't want to.

IMHO, you are a perfect candidate for the 16T. The above is all you lose and I think you gain a lot. Since you already have experience "cruising" in 4th, it should work even better.
I figure if I HAVE to get somewhere in a hurry, such that I NEED to use the Interstates, I will be in my car and not on the bike.

While your information on chain/sprocket wear is correct, you should be able to do a hundred miles or so with the 16T for a test and still go back to 15 with no ill effects.

I don't have but one interstate unless I'm leaving town and then I have to ride for at least two hours to find another one. :) Unless I get pressed for time such as a log trip where I need to get there before dark or to beat the afternoon heat and thunder storms I just take my time. On the way to work the highest speed limit is 45 mph.

I figured I could try it and if I didn't like it switch right away with out any problems. However, I will not rally know for sure until I get to go back up to the hill country again. I suspect that riding in fourth gear will take care of any issues I have with the 16T sprocket. I'll have one of each in the garage so making a comparison should be real easy.

[Easy Rider]

[ I suspect that riding in fourth gear will take care of any issues I have with the 16T sprocket. I'll have one of each in the garage so making a comparison should be real easy.

An advantage that most of us don't have! :roll:

I'm betting a pint of your favorite beverage that you end up with 16's on both. :tup:

[Gadzooks Mike]

I'm betting a pint of your favorite beverage that you end up with 16's on both.

I'll bet you're right, too!

[Water Warrior 2]

I would think that a lighter rider would benefit a lot more than a heavier rider with the 16 tooth sprocket.

[jonathan180iq]

I'm pretty lightweight. And, like I said, I love it almost every situation, save the long distance high speed rides.

[Jaime]

The GZ 250 has a good potential for performance mods. I've posted a new message at "Jetting: Part 1".
You only need 3$ and some DIY work to get a 'new' bike. :tup: