What Jets should I have

So the bike is running lean. doing the surging thing especially in the mid rpm range. they are the stock 76 kz900 carbs with cheapo pods running out to a mac 4-2. I had the thing re jetted at the local Kawi shop. The guy said he didn't have the jets so he drilled them. It runs way better than when I bought it, it wasn't even idling then. The "air filter" that was on it when I got looks like someone broke the stock air box leaving only the piece of plastic that connected the tubes. Then they made a little cage out of chicken wire. The guy said he just put a bandana on it. Anywho, I have been keeping my eye out for a stock air box, but until then I need to get the jetting right. Also, could adjusting the air screws help? How much correction can be done just using the air screws?

"So the bike is running lean. doing the surging thing especially in the mid rpm range." ...

Other than side wind gust, this would be your needle jet range... clip position change or different jet needle.

"I had the thing re jetted at the local Kawi shop. The guy said he didn't have the jets so he drilled them."..

You're kidding right... He friggin drilled out your carbs just because he didn't have them on hand :ohmy:

Ok, Main/pilot/air screw... whatever jets are we speaking of here?....

You'll need to find out what exactly did he put in there meaning what size for what carb etc....

NOTE: We can have the same exact setup but what we have in jet selections in our carbs won't necessarily work (be optimal) on yours, too many variables to contend with.

This is and can be a lengthy process even with BRAND SPANKING NEW CARBS! ... Now on a DYNO, they can get it done quicker and more accurately due to sensor placements for CO%, torque and HP measurements...

OMR

EDIT: For my CR specials but the concept is the same for most carbs....

Old Man Rock wrote:

"So the bike is running lean. doing the surging thing especially in the mid rpm range." ...

Other than side wind gust, this would be your needle jet range... clip position change or different jet needle.

"I had the thing re jetted at the local Kawi shop. The guy said he didn't have the jets so he drilled them."..

You're kidding right... He friggin drilled out your carbs just because he didn't have them on hand :ohmy:

Ok, Main/pilot/air screw... whatever jets are we speaking of here?....

You'll need to find out what exactly did he put in there meaning what size for what carb etc....

NOTE: We can have the same exact setup but what we have in jet selections in our carbs won't necessarily work (be optimal) on yours, too many variables to contend with.

This is and can be a lengthy process even with BRAND SPANKING NEW CARBS! ... Now on a DYNO, they can get it done quicker and more accurately due to sensor placements for CO%, torque and HP measurements...

OMR

EDIT: For my CR specials but the concept is the same for most carbs....

How can a dyno do it quicker and more accurately using horsepower measurements? To me that means helps find the biggest jet that motor can handle. CO% means how much trade off do ya want deal off to clean it up? Can't we just go back to the plug chop? Highway sighns that say NO PLUG CHOPPING! Dyno next five miles. And the billboard says Gunson colortune, with a pic of plummen smiling without his teeth in, holding up his burnt finger. What's the world coming to? So go tune your bikes on all that equipment, get it dialed, then when you get back just tell me what size jet it is and I'll drill some that size> Hey would it matter if my drill is a ... and yours is a ...... naa it shouldn't? Or would it? I'll have to think about that. OR did I pay someone to do that already? Let's see, I have an appointment at Jack's space age Technologies, there gonna shave me, then I go over to see the bike and choose someone to ride it...... I'm more for what the star on the Christmas tree looks like and the story behind it, not who put it there. Gotta go, watching a documentary on the great apes and what the hump is for

Put you bike in the signiture of your profile and it will help get a lot of responces.

Air screws are not going to help your on the road running.

That bike probably had 17/115 jetting.

Jeff @z1enterprises sell a Z1 air box. He can also get the filter and jets too. The Z1 air box is a lot easier to remove and install. Roy

@ nads...

I wrote "hey can get it done quicker and more accurately due to sensor placements for CO%, torque and HP measurements..."

I guess I should have been more explicative where with these other measurements would help you obtain a more optimum engine performance...

I guess I didn't feel the need to write down the whole Dyno procedure for him...

And considering he has new drilled out jetting to what size (unknown) and with all your vast experience, just what should he order from Jeff @ Z1 when he doesn't know what was installed (size or jet templates)... Meaning if the guy had to drill and tap, means he has some who knows what in there now so if he orders a set of OEM jets, good chance they won't thread in, too small...

Basically was meaning, maybe time for a professional to help resolve his issues so he can start riding again...

As for all your other rambling, dude, take your meds...

OMR

Who has meds?:blink:

I wish there were a dyno around here! The only one i know of is at a harley shop and they look at you funny when you ride a non Harley in.

No doubt on the Dyno....

I just was lucky on the first one (FREE) for one of the local shops has one on a trailer that they only use for promotional shows around the valley.... Dyno challenges.

In my testing, I informed the tech new motor build and I know I'm running rich an I was more interested in the rich/lean conditions more than total torque & HP results... He replied, cool, he'll keep her under 8 grand...

Almost emmidiately he informed me running way too rich and stated the same pretty much throughout the rpm range...
Basically... way too rich on the OEM jetting!

NOTE: Brand Spaning new Keihin 29mm CR Specials... Did the motor start and run as is... Yup... Is it optimum... HELL NO!

Even so, he informed me of 86HP at the rear wheel, no true flat spots overall pretty good results. Drop the Main jets to 108-110... The go for the mid & low range jets... Pretty much the same as Plummen and Larry C. informed me of in dicussions of the results...

This provided a good starting point for jetting... Time to do some research.... In speaking with several ppl I've learned have their shit together in these old KZ's and work on these old girls in a profession, I was turned onto the Gunson and Morgan units...

Sure, I could have had it done professioally, would have been easier, most probably cheaper in the long run but I wanted to learn this for myself.

In the mean time, take her through emissions where I expected to fail and did righteously so... Now I had my base line maurements to work from...

Now I know where I had to go... Based on the Jetting curves provided above and in the plug carbon conditions...

Drop a main and slow jet (pilot) size and raise a clip position from 4 to 3 thus lowering the needle jet... All in all, lean her out a little at a time for have a brand new motor here, too lean is not good! Got through emmissions with flying colors.

Presently still a little on the rich side for motor break in period where again, too lean not good... Once fully broken in ~ 1500 miles then I'll drop the mains to 112, slow jets to 56 and drop clip position to 2, maybe larger needle jet once completed for final optimizations...

All in all, do your research, jetting is a long out process to dial in your motor. What is good on mine isn't necessarily good on yours due to all the other variables.

A good dyno test will inform you where you are in rich/lean throughout your ranges of rpm operations, do you have flat spots in your curves, are you missing at points, what is your torque & HP throughout your rpm range. Look at your shop mauals, where do you think those curves where generated from....

Some Dyno facilities will even change your jetting and ajust your carbs accordingly, all depends on what you want to spend.... For those that feel where it stands is good enough, sweet, enjoy your ride as is, your bike.

Ok, I'll shut up now... :dry: :laugh:

OMR

start with a 117 main jet and a 20 pilot jet and the needle in the middle position and work from there get it running then start playing with perfection.

The bike runs, just not as well as it should. I moved the jet needle. it was on the fourth to the top, so I moved it to the last spot closest to the taper. It didn't help the problem. Will the z1 air box work on a 76? I heard that they were different. The surging is really noticeable whenever I back off the throttle. Thanks for the help so far, this site has been a real help.

www.wgcarbs.com/forum/index.php?board=3.0 look thru all the old posts on here and there should be a combo you could try that would get you in the ball park