info on redrilling jets

[Mantis88LX]

ok i have been reading alot about redrilling Jets and how that can help acceleration? so what is the jets and what do they do? were are they located? and redrilling i guess u just get a drill bit a little bigger than the stock opeing and drill it out bigger.

thanx guys

sorry for so many dumb questions. :P

[A20A1]

Well normally it's not that simple... jets have different shapes depending on their intended use. You can't just drill the hole larger without changing the shape of the jet as well.

I've looked at various jets from large to small... and i've realized that the larger the jet the more complex the shape of the jet becomes.

acceleration jets double in complexity as they even change the angle at which fuel enters the barrel. the acceleration jet cannot be changed on the keihin... it's best to use the FPR and maybe increase the accelerator pump diaphragm capacity.

the idle jet for the primary and secondary should be increased as well. only by .05mm though

[shepherd79]

i did on my old carb, i had 1.6 mm for primary and i think 1.9 mm for secondary( i can't remember for sure). they were too big. so now i have another carb and i just got 0.8mm drill bit and 1.2mm.
As Mike suggested i am gonna use 0.8 mm on primary and 1.2 mm on secondary( but i think it is already 1.2mm amy be larger).
i probably try to use 1.2 but it may be too big. i am not sure.
Mike how did you come up with the size for the jets?

[A20A1]

Huh? 1.60mm is smaller then the stock secondary main jet size.

and 1.60mm is too big for the primary main jet... so i suggested a 1.2mm main for the primary...

I posted the venturi size of the weber vs the keihin... though looking at the weber it seems I may have measured the keihin wrong... anyways.

Keihin venturi sizes were aproximatly:
22.225mm Primary
31.75mm Secondary

I did that rule of thumb I made up and I got this:
1.11125mm primary --- round up to 1.15mm
1.5875mm secondary --- round up to 1.60mm
by rounding up I try to leave the numbers in .05 increments, anything above .05 goes to .10 and so on.

turns out I was wrong and I posted that in the other thread... not about the rule of thumb but the measure of the venturi's... either that or the air-correction jets are extremely large and keihin needed to make the main jets bigger as well.

[POS carb]

it's not worth the trouble! I've done it, it just gets all weird plus you gotta make sure you don't leave little metal chunks in the hole

[shepherd79]

well that is why you get high speed drill, and compressed air.
it did worked nice on my old one, when my engine would reach 4k it would wake up and start pulling.