TOPIC:

I’m positive some of you remember my bike but if you do not then 81 kz750(4)H LTD. It ran 1800 miles this Rodin season but we got a late start so didn’t start till late august. The bike ran fine but plug chops indicate a slight lean issue. Revved fine through all RPMs. I bought a set of bigger jets for it, main and secondaries. From 125 main to 130. Then 62 secondary to 65. Started the bike after that and it ran like crap. Farrrr to rich, ran fine when cold but it would rev past 6k so I knew it was too large jet sized for a stock exhaust and no pods. Put the stock keys back in it and now we are going to try to shim it. I’ll attach a reference picture of what the plugs looked like and y’all tell me what size shims you recommend. 

also if I am correct here, the shim goes under the wide part of the needle, thus lifting the needle higher 

Anyone?

Yup, that is how shims work.

Those needles were never meant to be shimmed. I tried but could never get that big brass screw out. Was afraid I would bugger it up and from the look of the one in your picture I suspect you found it difficult.  I also suspect that for shims you may be on your own and getting an assortment of different thickness washers at your local hardware store and doing trial and error. Undiablo has a H LTD model and I know he was able to remove the needles like you. Cant remember if he shimmed them but have not seen him here in a while. You could search his posts

You say no pods and stock exhaust. Have you played with the pilot air screw ? I'd suggest  another 1/4 or 1/2 turn out from where they are now to start. Stock setting is 2 turns out from lightly seated and from the factory that was a tad on the lean side. I have found that  turning out beyond 3 turns out has no effect.

Fuel level in the float bowl will cause lean or rich running if lower or higher than specified (4mm) in manual .  Getting fuel level (clear tube method) correct across the board was major for how my bike runs.
 

wrote:

Those needles were never meant to be shimmed. I tried but could never get that big brass screw out. Was afraid I would bugger it up and from the look of the one in your picture I suspect you found it difficult.  I also suspect that for shims you may be on your own and getting an assortment of different thickness washers at your local hardware store and doing trial and error. Undiablo has a H LTD model and I know he was able to remove the needles like you. Cant remember if he shimmed them but have not seen him here in a while. You could search his posts

You say no pods and stock exhaust. Have you played with the pilot air screw ? I'd suggest  a 1/4 or 1/2 turn out to start. Stock setting is 2 turns out from lightly seated and from the factory that was a tad on the lean side. I have found that  turning out beyond 3 turns out has no effect.

Fuel level in the float bowl will cause lean or rich running if lower or higher than specified (4mm) in manual .  Getting fuel level (clear tube method) correct across the board was major for how my bike runs.


 

More turns out on the pilot screws is richer, not leaner.  I use 2.5 turns out as a starting point.  Agree that past 3 turns doesn't seem to do much.  I also agree that removing that brass screw is a bitch; I tried a few times on the dozen or so CV34's I've restored and gave up because the slot was getting buggered.  

Regarding shimming, be sure that when you lift the needle with a washer that there isn't any interference anywhere else.  For example, does the needle hit that brass screw?  Agree also that it shouldn't be necessary to shim the needle with a stock bike.  My KZ750 actually runs a little rich if anything.  Keep it stock and the bike will run fine if everything else is okay.

Thank you guys, so you think the bike is running fine even though the plug chop shows a smidge lean? The plug chop is from a 45mph around 4K RPM cruise so I didn’t figure the pilot system had much if anything to do with fuel flow at those RPMs. Also wasn’t aware at how difficult it was supposed to be to remove the brass nut. I actually just used a leatherman multitool flat head and it came right out. As far as being able to move the needle up and down there is no play so I believe the nut does contact the top of the needle. What shim thickness should be a start? 

#98 bit from a Chapman gun screwdriver kit fits tight in the brass screw and makes it easy to remove them. You can get individual bits from Chapman cheap.

wrote:

Thank you guys, so you think the bike is running fine even though the plug chop shows a smidge lean? The plug chop is from a 45mph around 4K RPM cruise so I didn’t figure the pilot system had much if anything to do with fuel flow at those RPMs. Also wasn’t aware at how difficult it was supposed to be to remove the brass nut. I actually just used a leatherman multitool flat head and it came right out. As far as being able to move the needle up and down there is no play so I believe the nut does contact the top of the needle. What shim thickness should be a start? 

It’s more important to know the throttle position than RPM and speed when doing plug chop test.

 

I see, but I do believe at that rpm I am at more than 1/4 throttle.

I have a larger set of screwdrivers that I will use to remove the nut if the rest become an issue. 

Post some pictures of the plugs. Compare to this article. 

www.dragstuff.com/techarticles/how-to-read-plugs.html

Well unfortunately I have deleted the pictures of the plugs after the chop however I did add the reference at the beginning of the article showing the exact pictures of what my plugs resembled. It is also showing full rainy days this weekend so I won’t be able to make another plug chop photo till probably Tuesday or Wednesday of next week.

Welp, carbs have been successfully shimmed. Using some stainless steel flat washers I have shimmed the carbs to .019” or just under .5mm. Not to worry I measured all shims with a micrometer and they all spec’d out great. Now the bike is running a beautiful tan color on the plugs and I have gotten rid of the popping after letting off the throttle. So happy with the way it runs now. Pulls great through all RPMs with no bogging anywhere.