carburettor identifacation

[stevegti2]

hi all was wondering if anyone could help me identify my carbs as i want to make sure they are the 32mm and not the 30mm ones . were is the mesurment taken from at a guess id say bellmouth/trumpet. also is it usual when redlining on while stationary the tacho jumps around alot it goes past 13000 but its like it cant keep up with the engine bouncing

cheers all info much appreciated steve

[masterofinsanity]

as far as i know the zxr400s were all built with 32mm carbs.

[RedexRobB]

theres 30mm and 32 mm carbs. I think it was L imports that came with 30mm carbs.

To measure, you'll need a set of vernier calipers and you simply measure the inside diameter of the carburettor outlet where the butterflies open and close

[masterofinsanity]

of all the manuals, microfiches, microfiche books and handbooks, flyers, mag articles, web specs etc etc they all state 32mm carbs.

[RedexRobB]

ive got 30mm on mine, i think all UK bikes had 32mm carbs, it wa the imports that had 30mm.

In fact the link you posted in martins thread, have a read what zimm said:

viewtopic.php?f=55&t=6763

[stevegti2]

cheers guys yes i was reading through old posts in the tuning section and thats when i stumbeled accross the 30/32mm carb difference will mesure on weekend when i check the jets and balance her up. will let you know what i find

thanks steve

p.s sorrey if i ask some silly questions i am a mechanic but have never really worked on carbs well before my time still not that complex i think just hate that you have to constantly adjust the things

[Vard66]

Hm.

Interesting.

Is there much difference in performance between the two carb throat measurements, anyone?

[jackdim]

I can also confirm that the import bikes have 30mm carbs and the UK ones have 32mm carbs, the import carbs also don't have any carb heaters. From memory the carb rubbers also have a smaller ID to restrict flow. Also import bikes have MUCH smaller cams with less lift etc and I'm assuming less valve duration so less power. Also the spark plug retainers seem a lot smaller for some reason??

I swapped cams, carbs etc over to UK spec ones on my import so now have a UK spec bike

[RedexRobB]

Well, i have 30mm carbs AND carb heaters, so not sure about imports not having them.

Not sure what the performance gains are, i suspect up top end, as mine tops out at about 125mph and will not go any faster even down hill.

[jackdim]

125mph seems quite low, I thought they were capable on average about 135mph? I'd be surprised if the 2mm between them made so much difference? Perhaps the cams?

[RedexRobB]

Well i have had 140 out of it, once. But not been able to revisit that since i rebuilt the bike, so maybe its not the carbs. Thing is, its got a Ti Beet system on it with a ASC free flow can. And since the rebuild the only thing ive changed is the can, so there might be the problem now i think about it Id really like to get it on a dyno at some point and see whats going on with it, as its got quite small jets too, 88 and 90 iirc. But the plugs are a lovely shade of toasty brown so that suggest its running beautifully.......

[Vard66]

Well, i have 30mm carbs AND carb heaters, so not sure about imports not having them.

Not sure what the performance gains are, i suspect up top end, as mine tops out at about 125mph and will not go any faster even down hill.

Same here. I have carb heaters, but I don't know which carbs they're on.

And the same deal with not rolling over 120, except currently, with it being downgeared, I'm struggling to hit 120 - it starts lurching and jiving under me when I get to about 118.