Needle notches

Bike is running very well BUT plugs burning very black. Not exactly sooty but decidedly black.

Will moving the clips to slot #2 from current slot # 3 possibly rectify the problem.

Thanks.

Would consider one size smaller pilot jet before moving the needle clip.

And assure float bowl fuel level is not too high.

Am assuming good compression amd a good properly timed spark.

Patton,

Compression real good across all 4.

Spark is RIGHT on the "F" on both 1/4 & 2/3 when dynamically timed at 1,200RPM and both advancing properly.

Corrently running 20's (Pilots) as we had bad stumble off idle using 17.5's.

I'll double check the floats and report back.

Thanks.

Hi Barney - I would suggest a plug chop to find out what is going on inside the engine.

As discussed here before, you can do a plug chop at wide open throttle for a mile or so on a deserted highway. I would suggest third gear as not to lose your licence in the event a law enforcement representative is nearby. Keep an eye on the tach and try to keep the bike below redline as not to grenade the motor.

Pull in the clutch after a mile of steady high rpms and hit the kill switch at the same time. Coast to the side of the road and remove the plugs. This will tell you how the engine is running on the mains. Never a bad idea to keep a set of mechanics gloves handy when playing around with hot engine parts.

This plug chop can also be done at steady half throttle which (if I am correct) will give you an indication of the lean/rich mixture on the needle clips settings.

I have been told that just letting the bike idle for five minutes with new plugs will tell you what the air screw setting and or pilot jet setting is like.

The plug chop is a simple and easy way to find out where the sooty plug problem may be coming from in the carb circuit.

Cheers-Colin Firth-Ontario Canada

Post edited by: reborn650, at: 2007/08/07 23:40

#1 clip is at the top of the needle so if u go from #2 to#3 u will raise the needle.this will make it run richer.u may be able to lean out the pilots a bit with the air screws, but as barrny says u should do a plug chop first to find out wich circuit is rich.u will probably find that the only way u can run for 1 mile near redline is at much less than WOT(probably 1/4 throttle).So u may not be on the mains.i find it helpfull to put a piece of tape around the grip and mark off lines at 1/4 1/2 3/4 and full throttle so u know exactly wich carb curcuit u are using.U may also find that u meed a few miles to get colour on a new plug.imo.i find that 90% of my riding is on the pilots 1/8 to 1/4 throttle.Hope this helps.

Post edited by: mark1122, at: 2007/08/08 01:18

Post edited by: mark1122, at: 2007/08/08 01:29

Your jetting is too rich (if the jetting is still the same as in your signature). If these are 76 KZ900 carbs, try #122.5 mains, go back to #17.5 pilots and 5DL31-3 on the jet needle (3rd clip position). The 76 carbs are pretty forgiving for use with pods/pipes, etc and just need a small bump in the main jet not the huge jump you made which is more applicable to a CV carb than a VM type carb.

WG, Well noticed re the sig line. I actually chopped the mains down to 118's a couple of weeks ago but managed to forget to amend the sig line.

The bike is running well right now but I will do the suggested plug chop and see what results I get. if I think my problem is needle height, I should ride hard 7,000+ for 2+ miles at 1/2 throttle position. Yes?

Should I clean the plugs before I start the process?

Do the different needles have differing tapers?

BTW, I bought me a neat little plug cleaner attachment for my compressor last week, $ 16 at Harbor Freight. Works extremely well.

mark1122 wrote:
[quote... find that 90% of my riding is on the pilots 1/8 to 1/4 throttle....[/quote]

Same here, and believe this applies to the majority of riders.

Once made the mistake of raising the clip position while seeking a leaner cruising mixture. Resulted in poorer acceleration through mid-range (gasping) and continued sooty plugs. Finally resolved by getting a perfect carb pilot circuit and correct service float bowl fuel level (mine was too high); and putting the needle clip back in the MIDDLE position.

When thinking about it, first remember how well the bikes performed off the showroom floor. (Yep, I'm that old). Then strive toward returning the carbs to their as-new condition. And try to avoid straying too far away from Ma Kaw's specs.

Agree a step up in main jet size may better accomodate a freer breathing exhaust system and/or air filter(s) at WFO throttle. But at 1/8 to 1/4 throttle (most legal cruising speeds), am thinking the clip position and main jet size are secondary considerations with far less impact on the sooty plug condition than is the pilot circuit.

At least that's what worked for me in dealing with the OEM KZ900LTD and Yoshi Stage II Z1 with 29's.

And I have no quarrel with the professional tuners using various non-stock jet needle tapers and slide cutaways, as they are undoubtedly far more knowledgeable and sophisticated than me.

Can still vividly remember the thrill of moving up from a Honda CB750 and putting a new freshly broken in Kaw 900 through its paces.

Patton, Good post bud.

One question....Guide me on how to acheive a "perfect carb pilot circuit? I'm in persuit of perfection (just like Lexus) but it eludes me. Thanks.

BARNEYHYPHEN wrote:

...how to acheive a "perfect carb pilot circuit? I'm in persuit of perfection....

You're probably already way ahead of me on most of this, but please forgive some of the excruciating detail submitted in hopes that maybe another reader might benefit from it. So here goes nothing ---


IMO, having a perfect carb pilot circuit is returning it to basically as-new condition.

As we know, freshly filtered air goes into a small entrance hole on the airbox side of the carb. (Sometimes there's an air jet, but oftentimes not). This air continues along a passageway until reaching the pointed tip of the pilot air adjusting screw which allows some of the air to continue on to the pilot jet.

Meanwhile the pilot jet has picked up raw fuel from the float bowl. The air reaches the end of the air passage at the pilot jet where the air goes through the lateral holes in the pilot jet creating an air/fuel mixture which mixture then travels from the top of the pilot jet on through the pilot passage and out the pilot outlet, from where the mixture is sucked through the intake valve into the combustion chamber.

All this is accomplished while the throttle slides are positioned completely down with no additional mixture contributed from the needle jet. And the pilot circuit continues this function of providing fuel mixture until about 1/8th to 1/4th throttle opening position. As the throttle is opened, the slides are raised, which allows increasingly more mixture from the needle jet and lessening effect of mixture from the pilot circuit.

At least the above is my over-simplified understanding of the pilot circuit system.

IMO, the pilot circuit is to blame for many of the sooty plug woes (and sometimes a too high float bowl fuel level caused sooty plugs regardless of an otherwise perfect carb).


Now, toward a perfect carb pilot circuit --- And there are undoubtedly other and perhaps better methods, maybe even far superior methods, but here's how I do it, until learning a better way.



Pilot Air Passage

The pilot air passage throughout its entire length from entrance hole at airbox side of carb throat to the pilot jet should be clear and ultra-clean.



Pilot Passage

The pilot passage from top of pilot jet to and through the pilot outlet should be clear and ultra-clean.



Pilot Jet

The pilot jet central hole and lateral holes should be clear and ultra-clean. The pilot jet itself should be in pristine condition and the proper size. Remember, possible damage from previous cleaning efforts (with wire or otherwise) may be visually imperceptible. Holes appearing perfectly round and clean may be faulty enough to disallow the absolute precision needed to properly meter fuel intake from float bowl and infusion of air from the air passage. As new pilot jets are relatively inexpensive, I prefer to replace them. Opinions may differ, but new pilot jets worked for me. And I have yet to see any visual defect in the old original pilot jets.


Cleaning The Passages

With carb on the bench, remove float bowl, float and pilot jet. Wear protective goggles. Plug threaded area where pilot jet was removed so as to block access into float bowl. If pilot air screw has been removed, block its hole with finger. Direct carb cleaner spray into air passage entrance and blast away until spray freely exits from pilot outlet.


Pilot Air Screw

Remove pilot air screw and examine pointed tip to assure it isn't damaged. Carb cleaner spray directed into the (1) pilot air screw hole has three places where it may exit, (2) Air passage entrance, (3) into float bowl through pilot jet location, (4) pilot outlet. Any two of these may be purposefully blocked so the spray flows between the other two. Spray every combination until assured all the passages are clear and clean as new.


And please don't rely on the upside down work-bench method of measuring float level. The clear plastic tube method of verifying correct service float bowl fuel level is much more accurate and works just as well with carbs on the bench as it does with carbs on the bike. And remember WG's time saving tip, only one float bowl screw is needed during the fuel level testing. Hold the carbs level. It won't leak. But possibility of a little seepage from the gasket area won't invalidate the test because correct level will be below the gasket.

Here's to Ya!

Post edited by: Patton, at: 2007/08/11 10:04