cylinder head mod! carb mod! muffler mod!

[pentax2]

This is my first bike a 2001 gz250.

And after a few months I decided to start making some changes, most of them came from this great site. (Thanks, very well done!).
Here are some of the things i have done:

-16t front sprocket.
-new exhaust, or as I call it "sound system".
-alarm system.
-free flow air filter.
- A much needed carb mode due to the exhaust and filter mods…

And it's great it really made a difference !!!

[burkbuilds]

Great looking bike! Tell us about the "differences"! A lot of folks mess with this model often with exhaust mods, carb re-jetting, etc, but most report that it didnt' make a lot of difference in performance. So what significant differences did your mods make? Like, are your zero to 60 times faster, do you have more top end speed, does the bike handle hills better, changes in fuel economy, stuff like that. If you have actual specs that's even better, but just your impressions would be good to hear if nothing else. Thanks for sharing, and by the way, how about telling us exactly what those mods were, like what exhaust pipe did you go with and what exactly did you do to the carb and the air intake? Even stuff like, how much it cost you to do this and how much time/trouble it was to do the mods would be appreciated, thanks.

[pentax2]

Well the first thing after buying it was to change the cylinder head because I bought mine with a cracked one… I bought a racked GN250 and took its head…

The second thing I did was the 16t front sprocket- made a noticeable difference in long cruses. It improved the fuel consumption to from 27(km/l) to about 31(km/l) (63.5 mpg to 73 mpg).
But the acceleration suffered due to the longer gear ratio, overall it's worth it.

The third thing was the "sound system" aka free flow exhaust no change in performance but a huge difference in the "look at me I'm driving a thunder" effect.

The forth thing was an alarm system nothing to say about it, it works.

The fifth thing was the free flow air filter and crab's main jet replacement (took a while to find the right one, 130 in my case) the bike became edgy (in a good way) and more responsive and another cool sound was add from the crab over 3/4 throttle open (sound of the engines breath).

[pentax2]

But the last mod was the biggest one, during the overhaul I performed on the engine (due to smoking and "oil drinking" from the engine) I decided to port the cylinder head, it improved the fuel consumption further to 35 (km/l) (82.3 mpg).
I took some photos of the process:

[pentax2]

And now the after:

[bonehead]

What did you use to port the head?

[pentax2]

and the installation:

[pentax2]

I used two similar tools for the job one the first is a micro air grinder and the second is regular air grinder.

[burkbuilds]

Great pictures, amazingly clear details! Thanks for sharing your work on the engine, nice job!

[pentax2]

I'm glad i can share it with people who can appreciate the work that's been put in to this bike.

[Water Warrior 2]

Excellent pics and a job well done. Cleaning up the rough aluminum casting is a good performance mod if you are already in there anyway.

[Maggie]

Wow, it sure is incredible to see the "guts". And they sure cleaned up beautifully. Thank you so much for sharing those pics and comments with us.

[Dupo]

Now thats some serious modding. Excellent!!





Interesting THIS thread gets no negative comments about going that extra mile modding a GZ. hmm.

[burkbuilds]

Since there didn't appear to be any "Loud Pipes" involved, we let it slide! :)

[patrick_777]

Interesting THIS thread gets no negative comments about going that extra mile modding a GZ. hmm.

Consider the lack of certain users in this thread also.

[mrlmd1]

Great job. How long did that take you?
Were you a mechanic of sorts before or was this your first motorcycle experience?
It's smart to lay everything out if you have room and take photos along the way when you disassemble something so that you can get it back together again and know where all the parts go and not have any left over or missing.
Now you just need an engine guard, windshield, sissy bar and luggage rack, saddlebags and guards, headlight/brakelight modulator, (anything missing?). and you'll be all set.
Seriously, nice job, looks good, especially with those stripes/graphics and that 2-tone seat. Red is the best!

[pentax2]

Great job. How long did that take you?
Were you a mechanic of sorts before or was this your first motorcycle experience?
It's smart to lay everything out if you have room and take photos along the way when you disassemble something so that you can get it back together again and know where all the parts go and not have any left over or missing.
Now you just need an engine guard, windshield, sissy bar and luggage rack, saddlebags and guards, headlight/brakelight modulator, (anything missing?). and you'll be all set.
Seriously, nice job, looks good, especially with those stripes/graphics and that 2-tone seat. Red is the best!

The taking it all apart is fast, if i work slowly and thoroughly about 30min.
the cylinder head modding and cleaning took about 12 hours: 4 hours for the porting , 4 hours for refitting the valves the last 4 was for disassembling and assembling the head it self and for the cleaning.

the work with the cylinder and piston is short but tricky, because you need time to cool the piston to the right temp. so you can measure the pistons skirt with a good micrometer, and the you just add 45 micrometers (0.001772") to that, and you have your desired cylinder diameter, after machining the cylinders inner wall you need to hone it, from what i understand it is best to use a 400 grit stones for it.

don't forget to cool the cylinder before you measure it, it should be around 25c (77f).

and every thing else is by the book.

[pentax2]

And yes this is my first bike experience...
a good place to start...

by the way the workshop manual is great!!! thanks !

[Easy Rider]

Interesting THIS thread gets no negative comments about going that extra mile modding a GZ. hmm.

Consider the lack of certain users in this thread also.


:neener:

[Water Warrior 2]

[quote=Dupo]
Interesting THIS thread gets no negative comments about going that extra mile modding a GZ. hmm.

Consider the lack of certain users in this thread also.


:neener:[/quote:2ewnulty]
:lol: :lol: :lol:

[RamAir]

Just Have a few Q's. First off great bike! And nice job!! You really got in there.
So did you buy the whole new piston head and upper part of the motor?
And you machined the cylinder wall why? Was something wrong?
Just to be clear you did this to revive the bike not increase cc's right?

So how do you find it runs now?, how many miles per tank/gallon?
How well can it take off and hold speed on highways plus hills?
And how fast you think it can go now? :whistle:

THanks a bunch!! :rawk: :2tup: :rawk:

[RamAir]

Hello??? I would like to do this next summer and I would like some kida reply? Is this guy still on this forum? Kuz what he has done here is supper great and I would love to put in the work if it yealds results!!


Also would like to try fully ceiling piston rings, in ceramic if they make them in our size that is!! Can take the heat and I might get .1 or .2 of a hp on them!! :2thumb: