The BIGGEST hesitation I have ever experienced

Dear Mr. Lesho and other members

I am a new member to KZ RIDER.COM and one who has recently looked at many of your archived posts, I am counting on your expertize to help me with a problem I am having.

I feel like someone going into someones restaurant and asking them to cook my hamburger, but here go's.

My problem is that the bike I am working on has the BIGGEST hesitation coming off idle I have ever experienced in the 45 years I have been riding motorcycles! The hesitation almost makes me look down to see if the engine fell out!

I am working on an old friends Rickman Kawasaki that has been sitting idle for some time now (In a heated garage.) The engine had just been replaced by my friend just before it was stored and I thing had not been ridden since. The engine looks to be in good shape, with reasonable compression readings of 140, 120, 120 130, with just a little shop running since it came into my hands. The engine had been removed and stored by it's former owner. It was, I believe, an KZ 900 motorcycle, (engine sn# is Z1E102586), and that bike it self was used for drag racing with an other engine installed back in the 1970's / 80s.

As for this engine problem, when start up cold, with full enrichner on and throttle closed, it takes some cranking and random cylinders trying to ketch till she finally starts up and is is firing on all cylinders. From then on, after getting a little heat in the engine, I can ride off with very little or no hesitation at all on full choke.The problem arises when I start to back off on the choke to keep the idle down to a reasonable rpm. This is where that bog comes into play. The more I back off the choke, the greater the hesitation till with it fully off the bike becomes undriveable. The engine will idle fine once warmed up some and the idle mixture screws are doing their job as I can both rich-in it up up and lean it out with all four the carb idle mixture screws. I have tried to over rich-en the idle mixture in hopes of helping with the hesitation but to little effect. The same with the slide jet needles. At half throttle, I can get the mixture over lean or over rich by moving then up or down in there clips but the hesitation is still a problem. The carburetors still has the stock jetting but the owner had has installed K+N filters and a four into one exhaust system. I have also checked the valve lash, points and timing. I have changed the spark plugs, run tested for intake leaks and have made sure it is running on fresh fuel. There is no sign of any spark problems as all plug caps can jump with a long fat spark with the motor running, so I see little chance of them all failing to fire properly under the cylinder pressure they will see under acceleration. ( blowing out the spark!)

I have scrupulously cleaned the fuel system from tank to petcocks to fuel lines and am getting good fuel flow to the Carbs. The Carbs themselves are in very nice condition with almost no apparent ware or signs of the dreaded home mechanic's pipe wrench tattoos. I have cleaned them completely and am getting a good flow of Carb. cleaner through all the internal passages, both low speed, high speed, enrichiner,
and and the jets.The jetting and settings are as stock for a 1976 KZ 900 ( as per Clymers carb. chart page 204). And they passed the bench test for slide synchronization. Floats have been wet set and are with in spec.

I would imagine the problem I have here is caused or aggravated by the changes made to the air filters and the less restrictive exhaust system now installed. My guess now would be to go up two steps on the low speed jets and see if that is of any help. I have disregarded the slide cutaway as it is stock? at 1.5 and I can't see it being much lower unless all else fails and I try knock off .050" to rich-en it up that way,

I hope I have expressed myself understandably, as I seldom do much, (one finger,) typing and, I hope you will find the time to drop me a small note with your views about the problem I have tried to described here .

Thank you.in advance for any advice you can offer me.
Ken Smith

Hello, Ken, and WELCOME to KZr forum!
We're glad you're here!

Regarding the hesitation coming off idle, if not already done, would assure correct ignition timing using a strobe type timing light. At idle rpm, align the F marks -- not the T marks. Ignore the T marks.

And also assure proper functioning of the advancer unit to confirm that it isn't hanging or sticking in the idle position.

Should be able to observe advancer instantly moving back and forth as throttle is blipped.

Is the engine from a 1976 KZ900 with oem carbs (Mikuni 26mm manual slide)?

Good Luck!

Welcome, in addition to checking timing, you said it now has PODs and a header on it and stock jets, the bike is running lean, I am not a carb expert, but I think the rule of thumb was to go up 2 sizes in jet for the PODs and header.
Hopefully someone who is way smarter than me can chime in on the jet size

Pods. :laugh:

what carbs are they lets begin there also what is your elevation. from experiance stock jetting with k&n's and a decent pipe will need at least the mains richened up substansaly also the needle settings should be richened up to the 4th clip position at the very least if they are stock 26's 0r 28's what mains are in it right now

Thanks for your reply. Yes, I have already checked out the ignition timing and the advance system. Timing light shows no indication of any advance problems with a seemingly smooth curve as the RPM increases to its maximum.
Ken

with stock 26mm carbs pods and a decent pipe i have my jetting as follows mains are 115's pilots are 20's and my needle postion is 4th from top. give that a try you will be pretty close if your below 2000 ft elevation try a 117 main or even a 120.

Thanks for your reply.
As I understand it, the main jet does not come into play until you are near full throttle. Until then the restriction on the fuel delivery into the air stream is restricted by the clearances between the needle jet and the jet needles taper. By raising or lowering the jet needle the clearance/area of the fuel restriction is varied up or down thereby richening up or lean out the fuel/air ratio.
This being so, I believe my hesitation is unlikely to be from too small a main jet as the throttle slide movement is
from idle to less than i/4 of its travel when the hesitation is present, (choke off).
As a guess I think the low speed jetting is the culprit.
Looking at the SUDCO catalog today I see they show a #25 pilot jet for the KZ 900 (76-77) while the Clymer manual shows the pilot jet for the same years of #17.5??
Time to get the order out for some #25's I think.

indianken wrote:

Thanks for your reply.
As I understand it, the main jet does not come into play until you are near full throttle. Until then the restriction on the fuel delivery into the air stream is restricted by the clearances between the needle jet and the jet needles taper. By raising or lowering the jet needle the clearance/area of the fuel restriction is varied up or down thereby richening up or lean out the fuel/air ratio.
This being so, I believe my hesitation is unlikely to be from too small a main jet as the throttle slide movement is
from idle to less than i/4 of its travel when the hesitation is present, (choke off).
As a guess I think the low speed jetting is the culprit.
Looking at the SUDCO catalog today I see they show a #25 pilot jet for the KZ 900 (76-77) while the Clymer manual shows the pilot jet for the same years of #17.5??
Time to get the order out for some #25's I think.

i m with Tim as far as suggestions,
not a carb expert, but a 20 pilot would get you closer to where you need to be.....
20 pilot 120 main and 4th clip the needle if they are 26's...just my .02....

main jet size and needle heights as well as the pilot jet has an effect all the way thru the rpm range as well as the various throttle postions if your lean in any one area it will have a serious effect on your ability to transition thru the various throttle positions.

the 25 pilot jet is to big for a stock motor it will cause it to be bulbbery and fat down low stick with the 20.

By turning the idle air screws in or out you can verify by rpm drops whether the passages are clear and flowing fuel. I'd check voltage at the coils, for low, like around 10 something. I had the same hesitation where the engine would drop off, this was also during take off, it was low voltage to the coils, or in essence a bad wire that supply's current to the coils. I was runing headers, and no filters at all, the motor was bored to 1015. It has 17.5 pilots. If you take off the pods and block the idle air passages at the carb opening near the bottom one by one it should drop rpm for each one. This will show fuel is flowing through the passages. I had slow starts as well and fouled plugs from the voltage drop to the coils.