GK76A GSXR 400RM - Poor Performance Please Help

[Andreasbe]

Dear All,

I have a GK76A that had some Carb issues, I followed the O-Ring guide to the T and it still is doing the same thing (Only a little bit mnore responsive and Semi Rideable)

I Took the bike to a Workshop and they found a compression issue, they checked the Valve clearance and managed to get the compression up to 2.5 from 2.0, this helped but the bike still dies when I wind the handle and open up the throttle (Goes up to 5500RPM then smokes and dies),

I suspect the Piston rings or sleves, but it might be the CDI.

Please could someone advice as I am dumb founded and in a complete stuper.
PS! I paid 27000 South African Rands for the bike, and have spent a further 20000 on repairs, I am now tired of spending and eager to do the job myself .!

[gsxr400 racer]

is it running on all 4?

[Andreasbe]

It does, I cant tell when im winding it, as it smokes when I rev the bike (BLACK), during Idle the bike seems fine and as long as I just twist the throttle slightly she can go up to 10000rpm before fluttering.

[Awynn]

Black smoke, oh dear that sounds fatal Must be burning some serious oil

[Andreasbe]

Thats why I was suspecting the rings. I just want a second opinion, as i need to take the bike appart myself, instead of using a workshop, I have spent enough cash on it and dont want another 10000 on someone else when I can just get a piston ring set and gasket set .! as it will set me back about 500 rand .!

[gsxr400 racer]

valve seals

[garynortheast]

Black smoke is NOT an indication of burning oil.
BLUE smoke - burning oil
BLACK smoke - over rich fuel/air mixture
WHITE smoke- weak fuel air mixture

The rich mixture could well be one of the reasons for the engine bogging down.

[Andreasbe]

What you say about the Black smoke meaning Rich Mixture does make sence, also if the bike was burning oil she would be smoking whilst ideling aswell, the only thing that confuses me is that I did the whole O-Ring saga, I have changed the Floater Valve ,MainJet, Slide and Idle mixture O-Rings, with propper Viton rubber rings. is there a possibility that the Main Jets or Pilot Jets change characteristics after some time and would need to be swopped out ?
If so does anyone know of any aftermarket brand of jets that I could use on my Gixxer (RM) 1992 (59hp) ?
(Stock standard Airbox,Filter, Carbs and Bore)

[gsxr400 racer]

worn out emulsion tube

[Austyn]

Hi mate, I've got some mainjets kicking around...drop me a message if you want a particular size, and I'll have a peek.
You say you've followed the carb 'o' ring guide to the letter....why not try a plug chop at idle and see what the mixture looks like (sooty black deposits = rich idle) then you can adjust the mixture to suit, (sorry if i'm teaching you to suck eggs! )
Well worth pulling the air filter and checking that too.
sounds to me like you're running far too rich low down, and as gsxr racers says it could be emulsion tubes...or could just be as simple as idle screws, float heights and mainjets.