GUIDE: Fitting new seals to your GK76a Carbs!

[oli_the_thread]

Right then, I'm all done fiddling with my carbs, one of mine needed a DAM good clean out after some piston/valve got inside, but I'm there at last, and with the help of people here did it all myself! I took photos through out in the hope of putting together a guide for other first timers out there taking this on!

Firstly set yourself up a little work area equipped with a phillips & 2 flat head screwdrivers (one mid size, one very small) a 4mm allen key, some rubber gloves, a small pot of petrol (for lube) and your O-rings



Then its time to crack on!
Remove the float assembly cover like so


You'll now find yourself faced with 3 O-rings to change (only two are under the cover, but all 3 are on this face)
3 O-ring positions shown here circled in red


Starting with the bottom one, make sure your screwdriver is a good fit in that little screw, I found them all to be bloody tight, so they'll need some weight on them to crack them off! once undone, pull the float assembly out and there is O-ring one! remove, lube replace and re-assemble! Simples


Next up is the middle one in the circled picture! VERY simple one here, get your flat screw driver in the slot and undo I found this pulls both parts out the carb instead of fiddling to get a spanner on there!
once again remove, lube, replace more lube and refit!

If the centre bit only comes out like below, get the spanner out and remove the rest! the o-ring is on the jet carrier, not the jet itself


next we do the top one, undoubtedly the most fiddly and one that got me most confused
get your little flat head in there and undo the screw, it will come all the way out, and more than likely have no o-ring on the end, there will also be a spring and washer inside that little hole, so gently fish them out too with a small screwdriver or something fine!


Thats the order they go back in, I found it easier to rebuild the screw assembly lube then re-fit like so


Screw that all the way in (dont forget your lube) then when it tightens up, make sure you then turn it back 1.5 turns!

Now bolt back on the cover and job done on that side!

flip the carbs over to the black plastic tops and undo both screws but watch out because there is a spring inside! take the cap off and check that the diapragm isn't torn or broken and as long as everything is good just change the o-ring next to one of the cap-bolt holes like so


then screw the cap back on being careful not to catch the diapragm in doing so and voila, that is pretty much your lot!


If anyone wants to add anything here (especially emulsion tube o-rings) please feel free or give opinions or advice!
Hope this is of help to some people :D

[ben2306]

so after that did you tune your carbs?
what will happen if the screws is turned 6 rounds instead of 1.5?
i'm thinking of taking it out to re adjust the screws cos my mech did 6rounds, but do i need to retune the carbs again? cos i dont have a carbtune.

[templin]

hi ben
its advisable to re-tune as with new seals the mix screw will sit at a different height in terms of turns out how did you count the turns ? 1 turn is 360 degrees of rotation of the screw the carb will react from 1/2 turn to 4 turns after that the aperture that the screw controls is in effect full open if your bike ran with pilot screw so far out i would suggest you check that the pilot jet is clear do a full strip and clean of all jets and channels oh and with changing the float o-ring re-check float height

as for lube use engine oil as some grades of petrol may cause the o-ring to swell slightly making the fit a lil harder when installing the o-ring have your small flat screw driver ready to give the o-ring a lil press to ad installment

[ben2306]

templin,
down here in spore, mechs !!
some shops dont even know how to take out the carbs... i'm not so sure, i asked the mech, he said 6turns, as he followed the old adjustment when he opened up. my plugs spoilt in 3months time, very sooty black. so finding the solution to it. i'm thinking of adjust the screws & see how but i dont have a carbtune..

[Variablevalves suck]

I would'nt be putting oil anywhere near the o'rings i supply, they are Viton, this is used for its petrol resistance and they aint cheap. A small amount of fuel or carb cleaner is enough, as fitting dry WILL cause them to cut up.
If you remove the pilot screw and think there is no o'ring left i would advise having a real close look up inside the hole as 9 times out 0f 10 its up there stuck to the casting of the carb, you dont want to be fitting a new o'ring up against an old one.

[ben2306]

sorry, i'm getting abit mix up with the mixture screw & pilot screw? are they the same? or the silver 1 is mixture screw? how about the bronze color 1? pilot screw? or the fuel jet?
1 last question, inside the carbs, only the silver screw is turned 1.5 out, right? the rest tighten. so sorry, although been riding this bike for 2years but still very blur...

[oli_the_thread]

Yeah thats right mate, make sure the rest are tight! I've not tuned the carbs yet as my engine is still in bits and I'll leave that to the mechanic who's rebuilding it

[ben2306]

guys, the top red circle is where the pilot screw sits. the 2nd circle is the main jet. my question is, below the main jet, there's a screw & hole. whats those for? how many o-rings supposed to change? i counted 4pcs. was wondering is it 5 as a mate here is selling 20pcs/4sets.

[stripes1976]

Not meaning to be critical but this guide does not cover all the o-rings and to a person without mechanical knowledge it could cost you more trying yourself than letting someone who knows how to do it.
This doesn't cover the gaskets under the jet block or the ones on the slide holder.
Removing the jet block is easy. Yet if you overtighten certain bits which is easy to do. You will write off a set of carbs!!!

[oli_the_thread]

I am more than happy to accept critisism, as said this is my first time so it was as much of a "have I done this right?" as a guide
I only covered the 4 out of 5 O-rings I was sent as I still haven't worked out how to do the other one, so any pointers on that would be ace!