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Brutus
18th April 2007, 20:43
any ideas on changing the piston to bigger size.
I have been told that the bottom end is the same as an XR 600.
anyone know what i need to do to make this happen?
what are the best carbs to use ?
I am in gissy and heard a few years back there was a GB owners club of sorts
operated by a bloke out of Napier?
Any leads?

tri boy
18th April 2007, 20:57
Think carefully about chasing a bit more hp from such bikes. Sometimes the end result can cost twice as much as trading up to a bigger/more powerful beast.
I know it's tempting, and with a bit of help from people in the industry great things can be created. However cost of parts, machining, and possibly less than spectacular results hp wise could make this an unwise choice. But if you have heaps of dosh go for it.

avgas
18th April 2007, 20:57
Spankme has a thread here somewhere on how to bolt the 600cc kit on. But there are about a million ways to get more stonk out of the good ol' gb. Google (with translation) about a million japanese sites on it.
The quickest fix i ever did on the gb4 was to preload the front forks with about $1.40 of the old 20 cent coins in each fork, and swap the back shocks for Koni's.
Didnt increase the HP at all - but the 0-100 time felt like it halved.
Also iridium plug is your friend. And it will only cost you $25 for that mod.
I also ran 5w50 (Visco5000) in it - as it offers the best of both world for the gb. Motul couldnt quite do the same unfortunately (i hate bp and love motul :( )
But search the threads as there are a few hundred on the ol gb's here.
ps: what year is yours? single or dual seat?

limbimtimwim
18th April 2007, 21:02
GB500?

10chars

deeknow
19th April 2007, 20:32
any ideas on changing the piston to bigger size.

There are a few threads with lots of links to sites on GBs already. Coincidentally I was just reading up on the same thing myself tonite, e.g.

http://www.kiwibiker.co.nz/forums/showthread.php?t=4661

They're great little machines arent they, I took an old workmates one out for a strop a couple of years back and loved it, do you reckon it'd put up with being a commuter?

Bonez
19th April 2007, 21:00
Take your GB400 add REALLY tight twisty roads. Fun. They tour no problem. And with a 300k plus fuel range the country is your oyster. I've posted plenty on KB about my Gbs sojourns.

tri boys comment is a very valid one btw.

MGST
19th April 2007, 21:54
You might be able to get a manual from davidsilverspares.co.uk I got a photocopy of the original Honda manual for my GB250 Clubman from him, cost $62 NZD all up on my doorstep. He has got heaps of genuine and pattern parts for just about every old Honda under the sun! Good luck . Choice bike!!:first:

mark247
22nd April 2007, 19:37
You might be able to get a manual from davidsilverspares.co.uk I got a photocopy of the original Honda manual for my GB250 Clubman from him, cost $62 NZD all up on my doorstep. He has got heaps of genuine and pattern parts for just about every old Honda under the sun! Good luck . Choice bike!!:first:

I have a pdf version of the manual. If anyone wants it just send me a PM.

GB's are awesome bikes! I have a guy looking at buying mine at the moment, if i get the right price i think ill just buy another one :P

Brutus
22nd April 2007, 21:22
Did the Waioeka gorge again yesterday, GB loves it.

Brutus
22nd April 2007, 21:31
They are great commuters. i didn't own a tin top for a few years and just rode the GB everyday for everything. Just got to get the cam chain renewed every 30000km,.

Thanks team for all the replys. Much appreciated.

avgas
24th April 2007, 17:02
They are great commuters. i didn't own a tin top for a few years and just rode the GB everyday for everything. Just got to get the cam chain renewed every 30000km,.

Thanks team for all the replys. Much appreciated.

Commuters? mine sat at 140 all night between auckland and tauranga. everyweekend.
Not to mention leaving the occasional ducati monster at the lights round town.
I found the dual seat more comfy than the single - anyone else had that?

Sanx
24th April 2007, 19:52
NOS. You know it makes sense :)

mark247
24th April 2007, 21:01
NOS. You know it makes sense :)

Easy as well, but do you really wanna melt your pistons?

Buddha#81
24th April 2007, 22:18
I brought a mildly damaged one when they first came out and hamered a solid piece of round bar through the baffles in the muffler and I'm not sure if I gained any power but it sounded farken cool.:yes: That was a way cool bike until my then girlfriend bined it into a cage.:gob:

avgas
25th April 2007, 21:00
Easy as well, but do you really wanna melt your pistons?
If i couldn't melt the NC20 no one can
I was as bad for that motor as Port Royal is for 14 y/o girls

kiwifruit
25th April 2007, 21:28
GB's are oarsome :yes:

Shadows
27th April 2007, 00:09
...do you reckon it'd put up with being a commuter?

I used one as a communter for a couple of years. It was absolutely brilliant for the job, it never missed a beat in that time. It was great fun on the weekends as well, what it lacked in the power department it made up for in sheer chuckability... in the twisties it would keep up with anything. Go for it.

I'd have another one myself, I wish I hadn't sold mine so damn cheap seeing what they go for these days!

bimotabob
27th April 2007, 19:12
Hi

A mate of mine had 2 of them, he bored one out to use a XR piston.
Problem was he blew up both engines.
Crank has no little end bearing and the conrod/piston pin area got hot and scored with that one.
The second picked up on the middle cam bearing and stuffed the head somewhat.
people are always looking for engine parts for these...could be a reason to look after it as these are nice cafe racers.

My advice is don't modify them unless you don't mind spending cash
and fixing it.

Did they make a twin cam model?
I know there is a 250 available (JDM though)

deeknow
28th April 2007, 09:58
I used one as a communter for a couple of years. It was absolutely brilliant for the job, it never missed a beat in that time.


Thanx Shadows, I've been tossing up between a GB and an SG350, my head says the Goose but my heart says the Honda, you guys may have tipped the balance towards the heart I think :-)

deeknow
28th April 2007, 10:10
My advice is don't modify them unless you don't mind spending cash and fixing it.

This is commonly seen advice, dont you reckon they'd make an awesome race class though if you could find enough of them. Just imagine a squadron of them thud-ing their way round a track. Might start stocking up on old engines from the wreckers :-)

BTW Bob, haven't seen you on the YB8 round Hamilton, is it reserved for special outings only? :yes: I was looking at the DB4 that NZVtwin had for sale in ChCh, finance etc fell through at the time unfortunately. Still keen on one, got any advice on issues to consider with one?

Shadows
28th April 2007, 14:05
Thanx Shadows, I've been tossing up between a GB and an SG350, my head says the Goose but my heart says the Honda, you guys may have tipped the balance towards the heart I think :-)

I think with bikes you should always follow the heart, not the head. Get the goose and you'll always be thinking about the other woman. Any way, if everybody used their heads all of the time, few people would ride motorbikes at all.


This is commonly seen advice, dont you reckon they'd make an awesome race class though if you could find enough of them. Just imagine a squadron of them thud-ing their way round a track.

I think there is a GB race class somewhere. UK I think.

HenryDorsetCase
28th April 2007, 14:11
I used one as a communter for a couple of years. It was absolutely brilliant for the job, it never missed a beat in that time. It was great fun on the weekends as well, what it lacked in the power department it made up for in sheer chuckability... in the twisties it would keep up with anything. Go for it.

I'd have another one myself, I wish I hadn't sold mine so damn cheap seeing what they go for these days!

I agree with that. I paid $4399 for one brand new in 1987 and sold it a coupleof years later for ~1800. it was the faired, single seat (basically unobtainable) model too.

ah well...

Shadows
28th April 2007, 14:29
I agree with that. I paid $4399 for one brand new in 1987 and sold it a coupleof years later for ~1800. it was the faired, single seat (basically unobtainable) model too.

ah well...

$700, good condition (4 years old). :rolleyes:
I was wondering why the guy that picked it up was smiling so much. He must have known something.

mark247
28th April 2007, 16:16
I agree with that. I paid $4399 for one brand new in 1987 and sold it a coupleof years later for ~1800. it was the faired, single seat (basically unobtainable) model too.

ah well...

The one DMNTD is selling at the moment for $2000 is single seat and has the fairing.

avgas
29th April 2007, 21:53
i sold my last 1 for $800, but she needed a new cam chain and rings. but i had new pegs, standard and aftermarket pipe, single and twin seat.
I felt bad cos i was working so hard at the time, didnt get to ride it.
+ that $800 was the last $800 towards the fz

Brutus
2nd May 2007, 19:23
My first one was purchased '97 single seat with fairing, 28000kms on clock. and a valve head fell in 5 days later. Superb chuckability and very forgiving if you stuff it up mid corner.
Its now in the shed hence asking for ideas. the carb is sticks in the rain, I have overhauled it twice and still no idea! Any other ideas for the carb? Is there a better carb to bolt in?

avgas
2nd May 2007, 22:04
My first one was purchased '97 single seat with fairing, 28000kms on clock. and a valve head fell in 5 days later. Superb chuckability and very forgiving if you stuff it up mid corner.
Its now in the shed hence asking for ideas. the carb is sticks in the rain, I have overhauled it twice and still no idea! Any other ideas for the carb? Is there a better carb to bolt in?
What is making the carb stick? i used to ride mine in tropical cyclones and left it parked outside for about 2 years without any problems
Butterfly jamming?

Brutus
3rd May 2007, 19:48
Butterfly appeared fine.
When I flood it with petrol(ie back flush) by putting hand over air intake and grab handful, this clears any blockage and is fine, until the next time.

avgas
3rd May 2007, 21:30
Got a dremel? using one of em' on the inside of the gb's carb is like a silk blanket on a waterbed.
Sex

mark247
4th May 2007, 09:19
Got a dremel? using one of em' on the inside of the gb's carb is like a silk blanket on a waterbed.
Sex

Are you talking about drilling out the jets? Thats what i was thinking of doing, i just dont wanna wreck 'em...

Brutus
4th May 2007, 19:50
Whats a dremel ? and what to do with such a thing?
Please excuse ignorance.

avgas
4th May 2007, 21:30
Dremel - drill grinder multitool thing. Similar to a dentist drill type setup with little drill, grind, engraving things.
I was actually thing more to clean up the inlets but you could do the jets aswell....if you were super careful.

mark247
7th May 2007, 11:04
Is it possible to get an oversized piston for the GB400?

avgas
7th May 2007, 13:51
Is it possible to get an oversized piston for the GB400?
Yep - how goods ya japanese. There is a guy there that makes anything and everything for the 400. I heard he was going out of buissness though. If i come accross his site again i will bump it on here. He made the 425 kit that was in my bike (according to the previous owner)

mark247
7th May 2007, 15:28
Yep - how goods ya japanese. There is a guy there that makes anything and everything for the 400. I heard he was going out of buissness though. If i come accross his site again i will bump it on here. He made the 425 kit that was in my bike (according to the previous owner)

Man i hope he is still in business!

avgas
7th May 2007, 22:06
Havent found it yet - but this looks nice.
Just like that old triumph triple i think.

PRETTY GB (http://64.233.179.104/translate_c?hl=en&sl=ja&u=http://www.beltlan.com/newpage22.htm&prev=/search%3Fq%3Dhttp://www.beltlan.com/newpage22.htm%26hl%3Den%26safe%3Doff%26client%3Dfi refox-a%26rls%3Dorg.mozilla:en-US:official%26hs%3D4Sz)

mark247
7th May 2007, 23:08
Havent found it yet - but this looks nice.
Just like that old triumph triple i think.

PRETTY GB (http://64.233.179.104/translate_c?hl=en&sl=ja&u=http://www.beltlan.com/newpage22.htm&prev=/search%3Fq%3Dhttp://www.beltlan.com/newpage22.htm%26hl%3Den%26safe%3Doff%26client%3Dfi refox-a%26rls%3Dorg.mozilla:en-US:official%26hs%3D4Sz)

Far out that thing is anything but standard, rear disc brakes, pegs further back...

avgas
9th May 2007, 12:00
I found this a good resource of information, when i was modding mine:
http://www.amy.hi-ho.ne.jp/tachi/english/gb400/tune_eng.html

moT
9th May 2007, 15:32
You could gut the exhaust drill holes in the airbox drill out the jet probably the easiest and least expencive way for a few more hp then if u wanna spend more $$$ think abt lumpy cams bore it out but really i would get a new bike for 2000 u cld get a bike faster than a gb400

FROSTY
14th May 2007, 20:15
um looks like noones suggested the easiest solution--ripout the 400 engine and bung in a 500 --never done it but probably doable

mark247
14th May 2007, 20:27
um looks like noones suggested the easiest solution--ripout the 400 engine and bung in a 500 --never done it but probably doable

Not many of those engines around...

okeh
15th May 2007, 17:32
Rip out the gb400 engine and dump in a SR20DET running 80 psi boost.

mark247
15th May 2007, 17:37
Rip out the gb400 engine and dump in a SR20DET running 80 psi boost.

Are you some Nissan car fag?

knuckleduster_13
5th September 2007, 22:22
hey buddy would like to have a copy of your owners manual in pdf:) i have a gb400
i joined this site theres a lot of us gb owners im from manila by the way
cheers

bob181
14th May 2008, 12:40
Hey I spent alot of $$$ fitting a big bore kit to mine along with cam, exhaust, shocks & wider rims. That bike was the just the best in this twistes, leave it in third and roll into corners then roll the throttle on out. Nice! Have just sold it to pay for a Ducati 600SS I brought, way different beast all togeather. I would look out for a XL600 motor, would bolt straight in and the wiring is the same. Probably need the XL CDI tho.

FilthyLuka
14th May 2008, 13:06
If the bottom end is the same as an XR600, why not just bolt on the XR600 complete top end? Head, Cylinder, Carbs? You would need to fabricate an exhaust i would imagine (custom chambers in Tamaki).

As far as taking a dremel to the ports goes, dinae do it laddy. Too much you can mess up if its your first time, see if you can find a junk head to practice on. I would just avoid the porting for the time being.

XR top end
Wiseco High Compression Piston
XR Racing Stainless Valves
Titanium Valve Springs and Keepers
Brass Valve Guides
Mikuni TM flatslide Carb (with accelerator pump)
Custom Exhaust headers going to either a big brand racing pipe (Yoshi, Arrow) or full custom exhaust

Personally, I think it would be great fun :-) But if its your only bike, i say leave it stock. The GB's are awesome even without fucking with them.

You could always just bolt in a CR500 Engine :doctor:

Brutus
15th May 2008, 20:34
I had sourced wiseco pistion etc and other internals. But .. think I may just visit Custom chambers and change carb.
I have trouble in the rain, sticky carb, but when I back flush the carb it clears(ie rev the nuts, put hand over air intake to choke it) it works til the next time. I've reconditioned it twice, but to no avail...
Leaving it stock is a good idea but always want more power when your 95kg.

mark247
15th May 2008, 23:10
I had sourced wiseco pistion etc and other internals. But .. think I may just visit Custom chambers and change carb.
I have trouble in the rain, sticky carb, but when I back flush the carb it clears(ie rev the nuts, put hand over air intake to choke it) it works til the next time. I've reconditioned it twice, but to no avail...
Leaving it stock is a good idea but always want more power when your 95kg.

I never knew Wiseco made a piston for them... I remember when i had mine it needed new rings and i couldnt find new ones ANYWHERE. I could of got some made i guess but i was on a budget.... so i put second hand ones in because i thought they were alright..... i ended up selling it up... Wish i didnt now, they are such a good looking bike.

Brutus
16th May 2008, 20:23
Yeah is was looking at making it a 500cc, after being told the 400 is a sleved 500, but I don't think this is quite correct.
I like it for the forgiveness it has especially with metzlers(?) but the old dunlop arrowmax is certainly a great tire for the GB. Hows the NC30?
i borrowing a 91 cbr 250rr at present and it is a bundle of laughs, think I'm rossi, well sounds like it at 18 grand. redlines at 19 but thats heinous!

mark247
16th May 2008, 22:32
Yeah is was looking at making it a 500cc, after being told the 400 is a sleved 500, but I don't think this is quite correct.
I like it for the forgiveness it has especially with metzlers(?) but the old dunlop arrowmax is certainly a great tire for the GB. Hows the NC30?
i borrowing a 91 cbr 250rr at present and it is a bundle of laughs, think I'm rossi, well sounds like it at 18 grand. redlines at 19 but thats heinous!

If you like the old GB400 you will like the NC30. It's just as much fun in the twisties only it actually has a thing called power.... haha. but in saying that my old GB400 was totally awesome for what it was, a thumper.

koba
16th May 2008, 23:15
Yeah is was looking at making it a 500cc, after being told the 400 is a sleved 500, but I don't think this is quite correct.
I like it for the forgiveness it has especially with metzlers(?) but the old dunlop arrowmax is certainly a great tire for the GB. Hows the NC30?
i borrowing a 91 cbr 250rr at present and it is a bundle of laughs, think I'm rossi, well sounds like it at 18 grand. redlines at 19 but thats heinous!

Entirely possible, many bikes have a 400cc jap version, rg400 with 45 horsepower is one example!

check this out for some related engrish!
Engrish GB specs. (http://www.amy.hi-ho.ne.jp/tachi/english/gb400/spec_eng.html)