What size jets are needed?

There are "starter formulas" that I have seen and as I recall, you go up one jet size (main and pilot) for the headers and one more for the air boxes. That's just a guess, then you tune it from there.

As to where to get them? You might try Bike bandit and see if the available OEM jets go up in size (they do for my 750).

There are also rejetting kits for a lot of bikes, the KZ1000 is so popular I would not be surprised if there were some for it. The internet search key is your best friend.

Thank you bountyhunter I appreciate the advice

bhanse said:

Thank you bountyhunter I appreciate the advice

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You might want to go to Bike bandit and click OEM and check the parts diagrams for your bike, they will show what jets were stock and which were optional.

I ran 4-1 and pod filters for a while on my 81 K1. Best results for me were using 140 main and 42.5 pilot but the recommended starting place is 140/40.

StarGate said:

I ran 4-1 and pod filters for a while on my 81 K1. Best results for me were using 140 main and 42.5 pilot but the recommended starting place is 140/40.

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I cringe to mention it, but..... if the pilots are the BS30/96 jets I just bought a bunch of them.... and the new size patterns are very different than the ones that came in my 1979 KZ750. My bike has the stock 40 and I bought a 45 back in 1981..... the new 45 is much smaller than the old 40. I needed a jet about halfway between my old 40 and old 45, and I ended up using a "new size" 57.5. I measured the jet hole diameter on a very long tapered needle that showed the distance it would slide on (pretty accurate). I picked the jet that was about half way between where the old 40 and 45 stopped, and it works perfectly (I am ignoring the fact it has 57.5 on it since that size would never work in my bike if it was the true size):biggrin:

I wish I had a microscope camera to post pics, because it really is true, the sizes are vastly different.

I guess I got lucky with that but I did surf a lot before finding a supplier for the jets I bought. This place specialized in jets and they were excellent replacement fits. I use to have the site on favorites but recently cleaned up my fav list and deleted it or I would have posted that for him. I started with the 140/40 and it ran great but still seemed to be a little cold natured on the start so I bumped the pilot up one size and that seemed even better. The starting point of 140/40 is straight from Wiredgeorge so you can't get much better info that that IMO. I

StarGate said:

I guess I got lucky with that but I did surf a lot before finding a supplier for the jets I bought. This place specialized in jets and they were excellent replacement fits. I use to have the site on favorites but recently cleaned up my fav list and deleted it or I would have posted that for him. I started with the 140/40 and it ran great but still seemed to be a little cold natured on the start so I bumped the pilot up one size and that seemed even better. The starting point of 140/40 is straight from Wiredgeorge so you can't get much better info that that IMO. I

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Well, like I posted in the other thread: some careful measuirng seems to indicate the new Mikuni jets I got are to spec, the old ones in my bike are larger than the stamped size on them. No clue how that's possible, even more confused as to why a Mac header needs a 57.5 pilot jet to run decent....?

But, it looks like the world is as it should be..... new Mikuni jets are good and Mac headers are worthless.

Put the airbox BACK ON and tow it with a VMax.