GS500FU BK4221 K4 derestrict

[ujtordai]

Hi Guys,

I have a Suzuki GS500FU BK4221 K4 bike. /25Kw/

My question first is how can I de-restrict it?
The 2nd. question is, is there anybody this bike with 15L/about 4Gal/ capacity fuel tank?

Thanks,

[redhenracing2]

De-restrict it? Intake, exhaust, and jets. It's not like it has a governor on it, it's a ~40 hp bike lol.

[Paulcet]

He's got a European restricted bike. About 34 hp.

[ujtordai]

De-restrict it? Intake, exhaust, and jets. It's not like it has a governor on it, it's a ~40 hp bike lol.

Maybe in the intake and exhaust hasn't difference. The differences are in the carburetors only.

What is your opinion?

[ujtordai]

He's got a European restricted bike. About 34 hp.

Yes it's true, by the factory really 34Hp.
I interested in what modifications are necessary to enhance the performance to 48Hp?

[007brendan]

I would recommend pulling the carbs and taking a look at the jets.  There's LOTS of information on the forum and wiki about changing the jets.  I also think that there must be some type of intake restriction as well, like a restrictor plate or something.

[the mole]

The carburettors are the same, just a small change in jet size. There must be some other modification, maybe exhaust or camshaft timing. Or there may be a restrictor in the inlets, between the carburettor and the cylinder head.

Sledge! Where are you oh guru of European GSs?

[ujtordai]

The carburettors are the same, just a small change in jet size. There must be some other modification, maybe exhaust or camshaft timing. Or there may be a restrictor in the inlets, between the carburettor and the cylinder head.

Sledge! Where are you oh guru of European GSs?

Is there in this forum anybody who successfully de-restricted a GS500FU ?

[redhenracing2]

He's got a European restricted bike. About 34 hp.

I stand corrected. I have no idea what the difference is between them.

[The Buddha]

I suspect its a stop in the slide. You can open the throttle but not get it over the 3/4 for slide opening. A plastic rod inside the slide spring would do it.
Not jets, that would cause it to knock before it would cut down the power output.
Cool.
Buddha.

[Miraz]

Pull the carb slides out, you will find 3 holes in the bottom of the slide.

The center hole is for the needle jet, so leave it alone...the outer two holes need to be sealed in order to allow the slide to raise fully.

It's usually done by drilling and tapping the holes, then sealing with a grub screw or some sort of bung....just make sure that you loctite it firmly into place, you don't want loose stuff floating about insider the carb.

[Paulcet]

I don't think that is right.

[007brendan]

Pull the carb slides out, you will find 3 holes in the bottom of the slide.

The center hole is for the needle jet, so leave it alone...the outer two holes need to be sealed in order to allow the slide to raise fully.

It's usually done by drilling and tapping the holes, then sealing with a grub screw or some sort of bung....just make sure that you loctite it firmly into place, you don't want loose stuff floating about insider the carb.

yeah, I don't think that's right either.  It's definitely some type of physical stop, either the rod in the return spring for the carb slides like Buddha suggested, or some type of plate on the intake side of the carbs, or in the airbox itself.

[Miraz]

The additional holes limit the vacuum draw against the spring, so the slide never opens fully....plug the holes and it works properly.

There are 3rd party restrictor kits that fit between the carb and head, but the original Suzuki restriction was a different carb slide.

[Paulcet]

So, If I plug both holes in my slides I'll get more power??   










(I'm being sarcastic.  According to the manual, if you plug both holes, you will have NO vacuum to raise the slides.)

[007brendan]

Where's Buddha?  The question about the extra holes in the carbs came up before.  It seems that three holes are normal, at least on American models.

Stock Slides have holes, 3 of them. DJ makes you block 1.5 of those. The third is the center one for the needle.
You dril lit, then tap it, then plug it. 
Cool.
Buddha.

http://gstwins.com/gsboard/index.php?topic=54326.msg612577#msg612577

[ujtordai]

The additional holes limit the vacuum draw against the spring, so the slide never opens fully....plug the holes and it works properly.

There are 3rd party restrictor kits that fit between the carb and head, but the original Suzuki restriction was a different carb slide.

Before 2004 the carburetor can be de-restrict easily, here is some image on this page:
http://akmt.hu/sufnituning/25kw35.html translated version from Hungary to English: http://translate.google.hu/translate?js=n&prev=_t&hl=hu&ie=UTF-8&layout=2&eotf=1&sl=hu&tl=en&u=http%3A%2F%2Fakmt.hu%2Fsufnituning%2F25kw35.html
But 2004 and after installed carburetors has more part then older.
I interested in how can I de-restrict this carburetor.

[007brendan]

Ah, according to those pictures, there's a hole on the FRONT of the slide.  Definitely don't have holes there on the American version.

[sledge]

The FU`s were low powered versions built in the factory to comply with the various learner laws that are in place in certain European countries, they are not full power versions with restricter kits fitted......they are just low power versions that have never seen more than 30 or so hp.

The carbs differ in the way of jetting and slide design, the exhausts are more restrictive and the ignition timing is slightly different so I would guess if you replace your carbs, exhaust system and the ignition advancer from a full fat GS500 you might see some gains 

The FU was never sold in the UK or the USA, Germany was/is the biggest market for the FU`s , perhaps you might get more info you need in one of their forums.

[Paulcet]

Ah, finally an authoritative answer! Thank you Sledge!