pilot jet richening the whole rpm range?

Does the pilot jet provide feul over the whole rpm range?? and thus richening??
I'm asking because I can not get my vm28 of my kz900 (1200cc) running well without pinging in the 4-8000rpm range. Tried serveral main jets,float heights and ignition settings. Still the 17,5 pilot.

martijn wrote:

Does the pilot jet provide feul over the whole rpm range?? and thus richening??
I'm asking because I can not get my vm28 of my kz900 (1200cc) running well without pinging in the 4-8000rpm range. Tried serveral main jets,float heights and ignition settings. Still the 17,5 pilot.

Yes, but as the throttle gets farther open, the pilot jet's contribution gets very small by comparison to what the main jet is putting into the flow.

vm28's are awfully small for a 1200cc motor. if u are running lean this will contribute to pinging.Also high compresion,advanced timing at the crank or cams.
do u have any porting done?

#17.5 pilot jets are what came stock on KZ900 VM26s (not 28s). If 28s are installed, what type? Jetting will vary depending on the type of carb assembly. And Mark, I doubt pinging is being caused by the carburetors. If it is pinging and there is an aftermarket piston kit, I wonder what compression is being discussed? Even 10.5:1 will ping on most all grades of pump gas.

the carbs are VM28sc (KZ900 1975 model)Calculated compression is 1:11,1 measured with warm engine and full throthle is around 185-195 psi pressure.

I know 28 mm is way to small but I'm not for top peak power. But with these carbs I can maintain the original airbox and air filter (and sidecovers)
Head has not been ported. It did run easily with 28mm carbs 11.000rpm in fourth gear... then it got scary

martijn wrote:

Does the pilot jet provide feul over the whole rpm range?? and thus richening??
I'm asking because I can not get my vm28 of my kz900 (1200cc) running well without pinging in the 4-8000rpm range. Tried serveral main jets,float heights and ignition settings. Still the 17,5 pilot.

At 11:1 compression, you are going to ping on pump gas unless you add some octane booster.

FYI:

www.batterystuff.com/fuel-treatments/OS6q.html

Octane booster is a poor way to deal with the pinging as it doesn't mix evenly in a tank of gas nor is it precise. I suggest you look into buying a Dyna 2000 ignition which will:

1. Give you retarded advance curves to tone down the pinging. I think there are 8 curves; 2 or 3 are advanced and 5 or 6 are retarded. You really need to retard the spark.

2. Give you a REV LIMITER - Any KZ engine spinning 11K rpm needs a rev limiter in the event a shift is missed. A bent crank or blown up clutch hub will result pretty quickly otherwise.

U could try thr dyna2000 as George said but they only have 2 curves for the 2 valve motors.But the higher compresion curve does advance a little slower so it will help with mid rpm ping. Of course, u can write your own curve too.
As George mentioned there are a lot of benefits with it. it also eliminates the old stock mechanical advancer completely.
Another option is to degree the cams for less advance.Say, 110 lobe centers. this will bring down the compresion and raise the torque curve.
Or install a thicker base gasket.

I was also of thinking retarding the intake cam..
I have not been able to test tke kz withe bigger pilot jets. It seems to have a complete electrical failure.
I'll let you know if there is any progress.
Just something about the ingnition. It is not an ignition timing issue. It is not pinging due a wrong timing. Even with 10 degrees full advance it keeps pinging....
That's why I'm looking at the carbs and the suggested intake lobe retarding might be the best to do.

martijn wrote:

I was also of thinking retarding the intake cam..
I have not been able to test tke kz withe bigger pilot jets. It seems to have a complete electrical failure.
I'll let you know if there is any progress.
Just something about the ingnition. It is not an ignition timing issue. It is not pinging due a wrong timing. Even with 10 degrees full advance it keeps pinging....
That's why I'm looking at the carbs and the suggested intake lobe retarding might be the best to do.

Even with 10 degrees full advance it keeps pinging.... --- perhaps misinterpreting, but am thinking ignition timing should be set more retarded (i.e., later) than stock timing to reduce pinging. If pinging when ignition timing is set to stock specs, it will ping worse if ignition is advanced ahead of stock specs. Firing before stock specs (i.e., set too far advanced) would be plug firing before the F mark reaches the permanemt timing mark on the case.

Just thoughts.

Good Luck!

you are right and that's what I did. Full advance is, when set to stock values 40 degrees btdc. I went to 10 degrees btdc. That is 30 degrees later/retarded. I experienced still knock, no power, not willing to rev and getting hotter.
Today wheater up her was miserable (rain) so no testride. I'll keep you informed. Thanks for your replies!!