1-2-3-4 125-128-128-125 I have a 1990 Japanese import that has been registered in Au. Bike has not been running for sometime, and I've bought it as is, and previous owner says 'it was running'... Lol classic line. It is a zxr250a2 1990 Anyway stripping the carbs shows the current main jets are ALL 114 Haven't checked the pilot jet yet. Airbox is standard, exhaust is standard. Is this standard from Japan for emissions? or is it just some jets chucked in there to sell the bike. 1. is the standard main jets 125-128 normal for all A-C models? 2. if 1 is yes, then I'l order the correct sizes based on standard airbox and exhaust. ordered the standard air filter, will check pilot jet , needle and float are set to factory, and get it running before I move to the next step of modification for performance, and can you get much out of these engines past factory? ie, open airbox, open exhaust, larger jets, iridium plugs, Race CDI, performance Coils etc. Or does this reduce the reliability, as I've done the basic mods above to many bikes without compromising reliability, but I suspect these 250's are already in a high state of tune being 19k rpm S.
The standard jetting is 125-128-128-125 but I know the race guys mess around with 108s & up, maybe you have the cv32 carbs which require smaller jets,I have 110s across all four at the moment on my bike.
@sharky your 250C engine should have 122:125:125:122 mains as standard. The slightly bigger ones are from the 250A engine. 250C engine has slightly bigger bore than 250A. 110's you say...how's she running? I've been thinking about trying some smaller main jets on my 250C engine, but I wasn't thinking of going that low. @stevodude what size are the carbs? if they're 32mm then you're a lucky dude.
My bike is actually a C model with an A model motor, loom & manual light switch, so i should have the slightly larger 125/128 jets. When I got my bike 10yrs ago it came with a C model motor,I couldnt get it to run right even with all new carb seals, good compression & valve clearances perfect, so I took it to a well known mechanic to have a look at, he couldnt "lean" out the carbs enough to tune it to his satisfaction either, thinking the jets had been bored out over time I ordered new ones but they made no difference, thats when we tried all manner of sizes until the 110s. I still have the same carbies & occasionally try the 122/125 jets out for comparison, I dont have any in between sizes to gauge off , i have really noticed with the standard jetting (122/125) the needle bounces around more & hits redline much quicker but feels like there is less usable power, the 110s handle a wrist full of throttle to with no hesitation, then again my bike isnt set up for the drag strip like yours,with a massive 16t front sprocket & 48 rear the 180 speedo is finished before 5th gear. The B race model zxr with 32mm carbs had 112/114/114/112 standard jetting I think. If i was @stevodude I would be checking the eng# & hope its a B there, which would mean much more than 32mm carbs which I have heard has poor throttle response compared to the 30mm, the B model has a kick *** gearbox & race cams, still dreaming of finding one.
Engine stamp is zx250ae Carb is 30mm throat diameter at the slide. Japanese engine search says its a zx250a2.
