Restricted Kawasaki GPZ500

[Len Dee]

I have a German spec restricted Kawasaki GPZ500. The restriction is not by washers as in the GB spec but by holes in the carburettor. Has anyone had any experience of derestricting this? It's a great machine but just lacks the ooomph!

[groovylee]

Second hand standard carbs from fleabay? Can be had for about £25
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Past - 1988 honda revere 600, 1996 kawasaki gpz500s, 1999 Yamaha R6

Current - 2002 Aprilia RSV1000R & 1999 Kawasaki ZX6R

[DJS]

Don't know how big the holes in the carb are but could you fill 'em in with epoxy resin or similar and then file/sand smooth? Pretty sure that epoxy is fuel proof.
Or is that too much of a bodge?

[Vincent]

Do you know where on the carb the holes are?
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Space Is Deep

[Vincent]

Here you go...one of Keiths old threads from VD :-

www.visordown.com/forum/workshop/german-gpz500/227899.html
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Space Is Deep

[Len Dee]

Hi Sorry for not coming back to this thread for a while and thanks to everyone for their contributions. As I had no idea where the holes were I took the first advice and bought a secondhand carburettor 25 Pound from ebay. Having now recieved the (new) carb. I found that there is 2 small holes on the diaphragm Piston on my original carb, not in the new so rather than Change the whole carb I just swapped the diaphragm Pistons and now my machine runs at full power just like a GPZ should.
I've attached a photo of the Piston, fill those holes and you have full power, (or swap them like I did).
Thanks again for all your advice.

[stinkwheel]

Thanks for getting back in touch about that one, interesting to know.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[garth]

[mysterious_rider]

would someone like to explain how this works? So the diaphrams leak so they dont rise like normal?
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KAWASAKIIIII

[Vincent]

The holes are in the slide rather than the diaphragm, just a guess but maybe as the slide gets to a certain height, air is sucked through the holes rather than sucking more fuel/air mix into the cylinder.
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Space Is Deep

[SteveZZR]

Just to keep it clear - the "Diaphragm Piston" as you called it, is a "slide". When I say piston I mean the suck-squeeze-bang-blow kind found in the engine.

CV carbs work by the suction of the engine drawing air through the holes on the engine side of the slide (on mine there are two small holes) What this basically does is the intake valve opens and the piston moves down it sucks air. When the air is drawn, it sucks air through the hole in the bottom of the slide which creates a vacuum above the diaphragm, lifting the slide up. The slide has a needle in it which goes through the main jet, the more it lifts the more fuel flow through the jet.

Short Version: Intake Valve opens, Piston moves down, Vacuum lifts diaphragm up, fuel flows through with air.

Those holes going straight through the slide mean that it will draw some air from the airbox rather than lifting the diaphragm as much as it should, reducing acceleration.


EDIT: forgot to mention, on a CV carb the throttle rotates a disc that is between the slide and the engine. More throttle means the slide is exposed to more vacuum from the engine and lifts further.

[Kickstart]