Welcome, Guest
Username: Password: Remember me

TOPIC:

Jet needle improves acceleration. 10 Jul 2011 18:36 #462121

  • calvin17d
  • calvin17d's Avatar Topic Author
  • Offline
  • Member
  • Member
  • Posts: 187
  • Thank you received: 1
It is a 76 kz900 a4.
Carbs: VM26ss
4:1 Vance and Hines with baffle.
K&n pod filters
New coil wires
120 main jets stock is 115
Stock 17.5 pilots
Needle clip position is 4 when stock is 3.
Valve shim clearances recently verified at .12-.15mm

Mark
That earlier post was my Attempt to explain the hesitation when aggressive throttling at a cruising speed.

The screws Peak rpm's at 1-3/8, 1-1/2, 1-1/8, & 1-1/4 turns.
1976 Kz900 A4

Please Log in or Create an account to join the conversation.

Jet needle improves acceleration. 10 Jul 2011 18:42 #462123

  • mark1122
  • mark1122's Avatar
  • Offline
  • Member
  • Member
  • Keep twisting it
  • Posts: 5350
  • Thank you received: 107
if it is running that bad with the needle up, maybe u should drop it back down and see where u are. if it is smoking black we are way off.

what changes did u make to the bike in the first place, before u started adjusting the carbs?
did u just add the pods ?
76 kZ, frame gusset work,1200CC.Ported by Larry Cavanaugh,This email address is being protected from spambots. You need JavaScript enabled to view it., 1.5mm.over intakes,.ZRX12 rear end,and seat,96zx9 front end.
01 CBR600F4i Track bike.
Cobourg,Ont.Can.

~ ~ ~_@
~ ~ _- \,
~ (k) / (z)

Please Log in or Create an account to join the conversation.

Jet needle improves acceleration. 10 Jul 2011 18:56 #462126

  • 78kzturbo
  • 78kzturbo's Avatar
  • Offline
  • Member
  • Member
  • Posts: 49
  • Thank you received: 6
the carbs you have are manual carbs when you open the throttle the slides open instantly.when you crack the throttle real fast there will be a little hesitation due to the fact the slides open immediatly to much air not enough fuel.it takes a second for the fuel to match the instant air.this is typical for manual carbs.1981 and up carbs have cv style carbs that run off vacume so when you crack the throttle there is no hesitation because the slides open from vacume keeping the air fuel mixture correct.

Please Log in or Create an account to join the conversation.

Last edit: by 78kzturbo.

Jet needle improves acceleration. 10 Jul 2011 19:16 #462129

  • 78kzturbo
  • 78kzturbo's Avatar
  • Offline
  • Member
  • Member
  • Posts: 49
  • Thank you received: 6
if you are running a stock pilot jet you will need to go up to a #20 if stock is 17.5 this will help you.more air means more fuel.when you use the k&n filters you will need to jet both main and pilot jets.i would start my jetting at 125 main & 20 pilots 1 1/12 turns on air screw.i like to throw as much fuel as i can and then work my way down.i would rather be a little rich than to lean. and work my way down.running to lean can hurt your engine to rich will just foul plugs.
The following user(s) said Thank You: firthy1

Please Log in or Create an account to join the conversation.

Jet needle improves acceleration. 10 Jul 2011 22:51 #462156

  • Patton
  • Patton's Avatar
  • Offline
  • KZr Legend
  • KZr Legend
  • Posts: 18932
  • Thank you received: 2145

calvin17d wrote: ...Am feeling like a smaller than stock pilot could help reduce the excess fuel at idle that has come at the hand of the raised needle....


Jet needle clip position has no effect at idle.
Raising the jet needle does not contribute additional fuel at idle.

The pilot circuit governs air/fuel mixture at idle.
Application of choke adds more air/fuel at idle.

Btw, who's on first? :lol:

Good Fortune! :)
1973 Z1
KZ900 LTD

Please Log in or Create an account to join the conversation.

Jet needle improves acceleration. 11 Jul 2011 01:55 #462187

  • calvin17d
  • calvin17d's Avatar Topic Author
  • Offline
  • Member
  • Member
  • Posts: 187
  • Thank you received: 1
I must have been fouling the plugs while making the screw adjustments. Or something else was making it smoke.

I put the needle back to stock and put in an order for a larger pilot. I had heard the pilot increase recommendation in the past but before knowing how critical they can be to operation I decided to shine it. Perhaps this will provide the the correct amount of fuel when needed.

Thanks for all the help. I am almost there. It runs so well and smooth from mids up. Just need to smooth out that low end transition?
1976 Kz900 A4

Please Log in or Create an account to join the conversation.

Last edit: by calvin17d.

Jet needle improves acceleration. 11 Jul 2011 03:24 #462191

  • bountyhunter
  • bountyhunter's Avatar
  • Offline
  • Member
  • Member
  • Posts: 7249
  • Thank you received: 336

calvin17d wrote: I did not get a chance to make any adjustments to the first run on the first gear test. I was unclear on how this should be done? If I had a rich result (surging) during my first gear test, would I simply turn the screws out uniformly and test again?

The screws only adjust the idle mixture. My carbs have a "pilot bypass" which is fed by the pilot jet but unadjustable. That is what runs mainly in the region just above idle at slight throttle opening. hence, the 1500 - 2k running at lightest throttle tests the pilot jet regardless of screw setting.

BTW: make sure the fuel levels are correct as that really affects low end response and pilot jet operation. Also, do a mechanical sync on the throttle plates to make sure they open the same amount. That can really screw up low end. I just use the smooth end of very small drill bits to set the throttle plates open a touch to sync the idle positions.
1979 KZ-750 Twin

Please Log in or Create an account to join the conversation.

Last edit: by bountyhunter.

Jet needle improves acceleration. 12 Jul 2011 11:19 #462441

  • calvin17d
  • calvin17d's Avatar Topic Author
  • Offline
  • Member
  • Member
  • Posts: 187
  • Thank you received: 1

bountyhunter wrote:

calvin17d wrote: BTW: make sure the fuel levels are correct as that really affects low end response and pilot jet operation. Also, do a mechanical sync on the throttle plates to make sure they open the same amount. That can really screw up low end. I just use the smooth end of very small drill bits to set the throttle plates open a touch to sync the idle positions.


I have spent quite a bit of time working on both of these. I used a sewing needle to sync the carbs to the clymer spec'd height.

1976 Kz900 A4

Please Log in or Create an account to join the conversation.

Jet needle improves acceleration. 12 Jul 2011 11:42 #462446

  • Patton
  • Patton's Avatar
  • Offline
  • KZr Legend
  • KZr Legend
  • Posts: 18932
  • Thank you received: 2145

calvin17d wrote:

bountyhunter wrote:

calvin17d wrote: BTW: make sure the fuel levels are correct as that really affects low end response and pilot jet operation. Also, do a mechanical sync on the throttle plates to make sure they open the same amount. That can really screw up low end. I just use the smooth end of very small drill bits to set the throttle plates open a touch to sync the idle positions.


I have spent quite a bit of time working on both of these. I used a sewing needle to sync the carbs to the clymer spec'd height.


As known, with manual slide carbs, the "bench sync" matches opening heights of the throttle slides at their lowest positions, which achieves a basic beginning position for the later "engine-running sync" using a manometer or vacuum gauges.

The engine-running sync equalizes performance among the cylinders, which usually results in slight differences in throttle slide heights of the carbs.

Good Fortune! :)

1973 Z1
KZ900 LTD

Please Log in or Create an account to join the conversation.

Last edit: by Patton.

Jet needle improves acceleration. 12 Jul 2011 14:36 #462469

  • TeK9iNe
  • TeK9iNe's Avatar
  • Offline
  • Member
  • Member
  • What did you do!?!
  • Posts: 2440
  • Thank you received: 26
Most differences in engine vacuum arent as slight as one would think.
The vacuum requirements of each cylinder are off by more than one can imagine.

The bench sync is almost uselesss except to just get the old engine to run. A proper vacuum corrected manometer sync is considered mandatory basic maintenence for proper operation, and not performing one leaves you guessing what other issues are at hand.

It doesnt matter how close you make those throttles/slides off the bike, either with micrometers, by eye, whatever - they are required to be at slightly different heights once installed, and the engines demands are then seen with the manometer.

No more bench syncing! Its useless and ametuer.

Get a good set of vacuum guages even...

B)
Motorcycle Shop Owner/Operator

79 Kawie Z1000 LTD
81 Kawie Z1000 CSR
83 Honda VT750C A
85 Kawie GPZ900 A2
86 Zukie GS1150 EG
93 Yamie XV1100 E
Lucky to have rolled many old bikes through my doors ;)

Please Log in or Create an account to join the conversation.

Jet needle improves acceleration. 12 Jul 2011 14:38 #462470

  • calvin17d
  • calvin17d's Avatar Topic Author
  • Offline
  • Member
  • Member
  • Posts: 187
  • Thank you received: 1

Patton wrote: As known, with manual slide carbs, the "bench sync" matches opening heights of the throttle slides at their lowest positions, which achieves a basic beginning position for the later "engine-running sync" using a manometer or vacuum gauges.

The engine-running sync equalizes performance among the cylinders, which usually results in slight differences in throttle slide heights of the carbs.

Good Fortune! :)


I assume this would be best performed once all the proper jetting and mixtures have been achieved, and as the last touch on the carburetor tuning?
1976 Kz900 A4

Please Log in or Create an account to join the conversation.

Jet needle improves acceleration. 12 Jul 2011 18:03 #462496

  • mark1122
  • mark1122's Avatar
  • Offline
  • Member
  • Member
  • Keep twisting it
  • Posts: 5350
  • Thank you received: 107

calvin17d wrote:

Patton wrote: As known, with manual slide carbs, the "bench sync" matches opening heights of the throttle slides at their lowest positions, which achieves a basic beginning position for the later "engine-running sync" using a manometer or vacuum gauges.

The engine-running sync equalizes performance among the cylinders, which usually results in slight differences in throttle slide heights of the carbs.

Good Fortune! :)


I assume this would be best performed once all the proper jetting and mixtures have been achieved, and as the last touch on the carburetor tuning?


Thats the way i do it.

my 1135cc motor had vm33mm smoothbores. those carbs dont even have a spot to hook up a sync guage, and she ran sweet.
i'm NOT saying dont do a sync, just that i get everything else close first.
u may still be way off on jetting. but i think u are getting there.
76 kZ, frame gusset work,1200CC.Ported by Larry Cavanaugh,This email address is being protected from spambots. You need JavaScript enabled to view it., 1.5mm.over intakes,.ZRX12 rear end,and seat,96zx9 front end.
01 CBR600F4i Track bike.
Cobourg,Ont.Can.

~ ~ ~_@
~ ~ _- \,
~ (k) / (z)

Please Log in or Create an account to join the conversation.

Powered by Kunena Forum