my new-old 1978 kz1000 is a 1137cc with hot cams!

I have pulled the carbs off and soaked in Berryman's carb cleaner all the inner parts except for the slide and slide actuator lever and choke, and using an eyedropper to drop Berryman's into the carb bodies, soft toothbrush to brush it in, let sit then blow off with compressed air, repeat.
And the jets etc. are actually soaking inside the can of Berryman's so the carbs will all be clean.

But A DEVELOPMENT, the bike has been modified from the stock kz1000 engine displacement: it has an "1137cc kit" and has hotter cams installed too, and the reason I need help is this:

- bike has a street-baffle 4-1 Kerker
- nearly stock airbox minus the 'snorkel box'
large black plastic thing that connects to the air filter box
- and despite all the above engine/intake/exhaust mods, the bike has ALL STOCK JETTING! I verified that all the jets in the carbs are the stock ones, whoosh it must have been running lean lean lean.

With 2 hotter cams, and with it bored out to 1137cc, and with the Kerker, and with extra amount of air on the intake side of the carbs since the snorkel box air restriction is not there ...especially with the 1137cc and the hotter cams, NO WAY should these carbs get reassembled with stock jets, right?

I was about to put in 110 mains and 17.5 pilots due to the 4-1 Kerker and the less-restrictive airbox setup, but with the 'hotter' cams (and I really don't know what this means, and the prior owner isn't recollecting it either, he's an older guy) and the 1137cc kit,
I am wondering:

1) what main jet should I use?
2) what pilot?
3) what position should the needle clip be at, or does the needle not require a change?
4) any other changes for the 1137cc + hotter cams situation?
5) does anyone know what the 'hotter cams' do?

Thanks for your advice, I want to get this running but not running super lean!

yeah it prbably needs richer jets. there are threads on here that go into jetting specs. the hotter cam means an aftermarket cam has been installed. they usually have more lift meaning they open the valve more and more duration meaning they hold the vavle open longer.hope that helps

Any time you add horsepower producing up grade, the engine requires more fuel. Bigger jets are a must.

try
Main Jet #142.5Pilot Jet #40,
1 and a half turns out.
center clip,

What type of carb is on it and what size? You state stock so are they the Mikuni smoothbores?

Are there any letters/numbers stamped on the cams? Look on the ends or near the cam sprockets. If there are, it will help with the recommendations for jetting, etc.

Hi folks, I can't tell about the cams as I don't have it apart, the prior owner told me recently about the hotter cams so I don't know what's in there. It ran fine for them but here's the issue with the carbs:

0) I have removed the bank of 4 carbs from the bike to clean them, and have taken apart the carbs and the jets etc. are all cleaned up using Berryman's carb cleaner. I took a look at the numbers on the jets (see below).

1) stock Mikuni carbs, which I guess means the Mikuni VM26SS, since the old owner told me the carbs are what were on the bike when he bought it brand new in 1978.

2) all stock jets: the mains are 105, the pilots are 15, all stock.

As Kano recommended:

"try
Main Jet #142.5Pilot Jet #40,
1 and a half turns out.
center clip"

WOWSA going from a stock main jet of #105 to a #142.5 is HUGE. And going from a stock pilot jet of #15 to a #40 is a big jump too.....

Is this a typo, or do the bigger barrels and cams require jumps of 105->142.5 and 15->40 ?

Thing is, the old guy rode this for years with this 1137cc and the 'hot' cams but using the stock carbs and all stock jets and 4-1 Kerker. It also has electronic ignition.

If the required jump in jet sizes really IS that big, is the fact that he had electronic ignition on it the main reason the bike didn't have detonation and, frankly, run so lean he'd burn pistons?

I'm coming from a 2-stroke carb-rejet-for-expansion chambers-and-K&N-air filters frame of reference.

105 to 142.5 is big, and 15 to 40 is big. Why didn't this motor, run for 12 years like this, blow up? The guy put over 10,000 highway miles on it with the 'hot cams' and 1137cc performance mods and 100% stock carbs and stock jetting.

I'm a tard vis-a-vis 4 stroke tuning I reckon! NEED HELP!

Kano, people in the UK conquered the planet. The great British Empire has left its mark.

Furthermore, I see you have 1147 posts, wow. Did the extra info above help to clarify this bike? I'm really *shocked* the old guy got over 10,000 miles with STOCK JETTING. In fact, I have new respect for 4-stroke bike engines in terms of their ability to keep running despite owner abuse.

I thought the fact he got over 10,000 miles on it with the 4-1 Kerker and modified airbox with stock jetting was odd. After the 'cams + 1137cc' info I'm shocked.

I'll go with the #142.5 mains and the #40 pilots, Kano, if the above info has clarified it! What do you think?

Before you put any more time or money in the carbs-DUMP THEM! 26's are useless on a stock motor and will kill performance on your motor. I would look for a set of 33's on ebay. They should run you around $500 or so but well worth it.