cold starting

[Alexander]

Agree Alexander, the pilot circuit provides trim for the entire range but he wont have it.
That diagram is slightly mis-leading when you're talking about CV's because the rest position for the throttle ''''slide'''' is approx 25% open.
AL[/quote]

Yes Al, I was of course referring to slide carbs and as you have pointed out there is significant differences to CV'S of which I am not familiar and therfore unfortunately unable to offer much more in the way of advice to Gazza's problem, it does sound like you are on the right track now though, the bike requiring Gazza's intervention with restricting the air intakes does suggest weak mix and I suppose CV's would rely more on adequate vacume to operate properly? Alex.

[Pigford]

Main thing when tuning the carbs is to get the main jet right - as this has the most effect on the mixture & is where any weakness will cause most damage. Once thats sorted its then working back to the needle position for mid range trimming and finally the pilot system.

Yes, all parts of the system will have an effect on the mixture, to different extents

[Alexander]

Main thing when tuning the carbs is to get the main jet right - as this has the most effect on the mixture & is where any weakness will cause most damage. Once thats sorted its then working back to the needle position for mid range trimming and finally the pilot system.

Yes, all parts of the system will have an effect on the mixture, to different extents

Hi Pigford,
I agree this makes sense, you should always start at the main jet and if need be progress on to the needle and pilot.
However you cannot stop there because if the pilot jet is changed the main jet will be affected by this change and need recalibrated again, generally you must, start with the main jet and finish with the main jet, you cannot change the pilot jet and assume the main jet is still ok. As I previously tried to explain (Not too well) the pilot jet does not only contribute to the first ¼ throttle. It is contributing fuel right up to full throttle and likewise if the pilot jet size is reduced you will more than likely need to increase the main jet as it could be leaned off and lead to serious engine damage such as holed pistons as you mentioned before. It would be great to simply start at the main jet and finish with the pilot, but carburetion set up is much more complicated than this.
Most of us who find a need to adjust the jetting of the carburetors are usually doing so due to minor changes such as 4 into one exhaust or fitting bell mouths etc to an another wise fairly standard motor and these changes usually only require minor adjustment to the main jet, possibly 10 to 20%.
But with more significant engine mods, fitting an engine with different carbs or like Gazza here, installing carbs to a previously fuel injected engine there is no bench mark to start with.
Unless someone has already done the same mod and is able to advise what was finally used so will provide a good starting point and with some luck no need to make any change.
I think the point I am having difficulty trying to convey to you is the role the pilot jet plays, it does not simply stop functioning beyond ¼ throttle and it will have a say in determining the most suitable size of main jet. If the pilot is changed, fuel calibration at the other jets also change and sometimes by a surprising degree, this is true to all the jets but more so to the pilot as it is the only jet that influences fuel supply from 0 throttle to full throttle by the greatest degree (as can be seen in the diagram), or as Al put it better the pilot provides the TRIM.
Any change here will more than likely necessitate a recalibration of the Main Jet and or Needle jet. Things can get a lot more complicated the more heavily modified an engine is. I have heard it said that when the engine tuners and would be racers got their hands on the first z9’s the standard carbs were a nightmare to set up, not so much a problem for racing as the bike is run at full chat most of the time so flat spots and poor tick over were not an issue, but it is suggested this is what led to the introduction of the hens teeth 29mm smoothbores much favored by engine tuners.
There are many other components to a carburetor such as throttle valve cut away (2.5mm I believe on Z1 and 1.5 on most later versions), air jets and varying tapers to the needle jets etc just to make finding the perfect set up more elusive, it is possible to have a an engine modified to the extent its fueling requirements are beyond the adjustments of the original carburetors pilot, needle and main jet, and even the carburetors may need to be replaced with something more suitable.
It would be great if there was a simple step by step rule to lead you to the perfect set up but there are hundreds of variables which are why having a good starting point is crucial and making small adjustments at a time.

[Pigford]

Main thing when tuning the carbs is to get the main jet right - as this has the most effect on the mixture & is where any weakness will cause most damage. Once thats sorted its then working back to the needle position for mid range trimming and finally the pilot system.

Yes, all parts of the system will have an effect on the mixture, to different extents

Hi Pigford,
I agree this makes sense, you should always start at the main jet and if need be progress on to the needle and pilot.
However you cannot stop there because if the pilot jet is changed the main jet will be affected by this change and need recalibrated again, generally you must, start with the main jet and finish with the main jet, you cannot change the pilot jet and assume the main jet is still ok. As I previously tried to explain (Not too well) the pilot jet does not only contribute to the first ¼ throttle. It is contributing fuel right up to full throttle and likewise if the pilot jet size is reduced you will more than likely need to increase the main jet as it could be leaned off and lead to serious engine damage such as holed pistons as you mentioned before. It would be great to simply start at the main jet and finish with the pilot, but carburetion set up is much more complicated than this.
Most of us who find a need to adjust the jetting of the carburetors are usually doing so due to minor changes such as 4 into one exhaust or fitting bell mouths etc to an another wise fairly standard motor and these changes usually only require minor adjustment to the main jet, possibly 10 to 20%.
But with more significant engine mods, fitting an engine with different carbs or like Gazza here, installing carbs to a previously fuel injected engine there is no bench mark to start with.
Unless someone has already done the same mod and is able to advise what was finally used so will provide a good starting point and with some luck no need to make any change.
I think the point I am having difficulty trying to convey to you is the role the pilot jet plays, it does not simply stop functioning beyond ¼ throttle and it will have a say in determining the most suitable size of main jet. If the pilot is changed, fuel calibration at the other jets also change and sometimes by a surprising degree, this is true to all the jets but more so to the pilot as it is the only jet that influences fuel supply from 0 throttle to full throttle by the greatest degree (as can be seen in the diagram), or as Al put it better the pilot provides the TRIM.
Any change here will more than likely necessitate a recalibration of the Main Jet and or Needle jet. Things can get a lot more complicated the more heavily modified an engine is. I have heard it said that when the engine tuners and would be racers got their hands on the first z9’s the standard carbs were a nightmare to set up, not so much a problem for racing as the bike is run at full chat most of the time so flat spots and poor tick over were not an issue, but it is suggested this is what led to the introduction of the hens teeth 29mm smoothbores much favored by engine tuners.
There are many other components to a carburetor such as throttle valve cut away (2.5mm I believe on Z1 and 1.5 on most later versions), air jets and varying tapers to the needle jets etc just to make finding the perfect set up more elusive, it is possible to have a an engine modified to the extent its fueling requirements are beyond the adjustments of the original carburetors pilot, needle and main jet, and even the carburetors may need to be replaced with something more suitable.
It would be great if there was a simple step by step rule to lead you to the perfect set up but there are hundreds of variables which are why having a good starting point is crucial and making small adjustments at a time.

Cheers Alex... My Z1000 is 1075 with a gasflowed head and I'm running RFS36's with K&N's. I have tuned them by "seat of the pants" and after that took it on a dyno - and it was running a real linear output with fuel ratio a tad lean at around mid 13's. So my tinkering was only a smidge out and I had to increase the mains from 135 to 140 - sorted. This bike runs regular 1/4 miles at 11.5 secs.

Also tuned my old Gixxer 1127 - RFS 38's, and that run great.

What modified bikes you sorted out then

[Alexander]

If you do have to increase pilot jet you have to down size main jet but would leave as to see if cold start is sorted, would confirm step in the right direction. Opening throtle on weak fuel start up would not help starting as others have said so try and avoid this. Good luck, Alex.

Don't want to pick holes, but if the bike runs OK when warm - do NOT reduce main jets. The pilot & main systems are seperate, and when over 1/4 throttle, the pilot doesn't have much say in the mixture. If you reduce the main, it could run too lean = holed pistons

Thats great Pigfgord, would think you would know the basics then before you started picking holes, the pilot and main systems are not seperate and does have a significant say in the mixture contrary to your statement above, but hey flying by the seat of your pants often works so well done, I am truly impressed but dont't you think this debate needs putting to bed. Poor Gazza's probably given up, chucked his carbs and refitted his injection by now, and don't take it too personel, what makes this open forum great is the willingness of others to share there experiences or expertise to help a fellow member and we all won't always get it right but the important thing is everyone should feel comfortable to contribute should they wish without fear of retribution. Alex

[kev edwards]

Any progress Gazza

[gazza]

sorry boy's no progress as yet, waiting for some parts from kawasaki , will keep you posted ,thanks gazza.