Another non starter

[VA]

Would appreciate any help in getting this GK73A firing, it just won't start, I have good spark so I know it's not that. After checking the plugs after a burst on the start button, they don't seem to be getting any petrol. I've taken the carbs apart and cleaned the jets, checked the float heights, pilot screws to where they were when it did run, I've even changed all the o-rings. What would stop fuel getting to the plugs ??? I know the carbs could do with balancing but by eye the butterflies are very close in position, would that stop it starting ??, also I'm trying to start it with the airbox off, would that stop it starting ?

I did notice that where the airbox fits on to the carbs, at the bottom of the carb(s) inlet(s) there are 2 small holes (forgive me not knowing the technical term) and when I tip the carbs back slightly I get petrol coming out of those two holes but only on one carb, anyone tell me what is going on here, should that happen?

Any help would be great, thanks for your time.

[Hadies]

at the bottom of the carb(s) inlet(s) there are 2 small holes

Are you referring to your float bowl drain tubes/holes? Have you checked that the float bowl drain screws are tight enough?
And throw on the airbox for safe measure.
Good luck

[Jaicen]

I don't know about the earlier models, but the GK76a has a vaccum tube which feeds the carbs, and also monitors the air pressure in the airbox, which may have some bearing on your non-starter.

[VA]

OK, I have managed to get it started, installed the airbox and it fired, funny though because I have had this bike running previously without the airbox. Anyway, although it started it ran like a dog and cut out as quick as it fired up, I have set the pilot screws to 3 turns out as that is where it was previously, can anyone tell me what the pilot system entails so I can try to get this thing to idle i.e. does idle have anything to do with needle height (clip position). What size jets should I have and if they are bigger or smaller than standard what problems would this cause.

Many thanks

Edit:- Ok, I decided to go back to the book and change the pilot screws to 1.75 turns out and yes,it starts and sounds better, but it will not idle nicely,the revs go up a bit and then fall to where it's hunting for fuel,turning the idle screw just increases the revs to @4000, but still no nice idle, as soon as I touch the throttle it dies, should I be looking at a richer mixture ?? any ideas ??

[arigon]

try balancing the carbs up if youve had them appart they will defo need ballancing

[VA]

Ok, I have now spent some time working on the set up and have adjusted the valve clearances, stripped & cleaned the carbs, new o-rings, balanced the butterflies by eye (looks ok to me), repaired frayed/broken wire on the pick up coil and have good resistance, also checked primary & secondary resistance on the coils and all good, and have new plugs.

It's starts good but just on the slightest blip of the throttle it will bog down but I can rev through it, but you can hear it bog just for a fraction of a second, also no choke needed to start, although the ambient temp is +30°c. I have set the pilot screws & needle positions to where they were before I stripped it, which for the pilot screws was 3 turns out, rich I know, could this be making it bog down, it used to be ok like this pre valve clearance, the intake valves were all @ 0.10mm and are now @0.15mm, the exhaust valves were also tight, so could the previous pilot screw setting now be too rich and making it bog down ???

Any ideas ??