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Carb Issues 17 Oct 2018 01:30 #792416

  • Kz44018
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I recently purchased a 1982 kz440 LTD Belt. It had the airbox removed and air pods installed and also the baffles cutoff. I ordered a jet kit from Sigma Jet kits and I installed it. I put 102.5 mains and 87 primarys and also put one metal shim with also the nylon shim your suppose to install with it. When it runs it backfires on idle a little and when you rev it up in Neutral it backfires, It also does it when downshifting. I also noticed I can only go 45 mph in 6th gear. When I checked the spark plugs they were white on the top. I was curious if anyone could help me figure out what's the problem.

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Carb Issues 17 Oct 2018 01:41 #792417

  • Warren3200gt
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White plugs means your running way lean. But on which jet needs to be determined or possibly both. When its back firing on idle is it through the carbs or exhaust? If through the exhaust it could be unburnt fuel igniting. Have you colour tuned it?
Cutting out the baffles will mean you will hear things which were happening before but was masked by the baffles.
Changing airbox and exhaust and carb kits all in one go is a recipe for problems. Golden rule is to only change one thing at a time, test it and document the result. At least then you can keep track of what change is causing what effect.

Z1000J2 somewhat modified!

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Carb Issues 17 Oct 2018 12:15 #792443

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What is colour tuning? Its backfiring through the carb I believe. I'm thinking of going up higher on the main jet.

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Carb Issues 17 Oct 2018 14:11 #792450

  • Warren3200gt
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I dont know anything about your model so only give general pointers. Do you have a workshop manual? You need to ensure the carbs have the correct fuel float heights, and are set up mechanically as per the manual.
You can download one here www.manualslib.com/manual/1004585/Kawasaki-Kz440.html
Once you happy that the carbs are set up correctly you can move onto fine tuning with a colour tune.
A colour tune is a effectivly a spark plug that allows you to see what colour the fuel air mixture is burning. Orange is rich, blue is lean. At tick over you are trying to achieve the boarder between the two. Orange with a tinge of blue. This is done using the mixture screw. If you cant get blue then the pilot jet is too big. If you cant get orange then the pilot jet is too small.
Once you get idle burn colour correct you can move on too other rev ranges.
Understanding how a bike carb works is critical to tuning for best results. The best laymans terms explanation I have found is this www.iwt.com.au/mikunicarb.htm Worth reading and understanding before you drive yourself mad. Its easy to get lost for the uninitiated and I suspect was the case with the previous owner.

Z1000J2 somewhat modified!

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Carb Issues 17 Oct 2018 17:33 #792456

  • 650Dude
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Kz44018 wrote: I recently purchased a 1982 kz440 LTD Belt. It had the airbox removed and air pods installed and also the baffles cutoff. I ordered a jet kit from Sigma Jet kits and I installed it. I put 102.5 mains and 87 primarys and also put one metal shim with also the nylon shim your suppose to install with it. When it runs it backfires on idle a little and when you rev it up in Neutral it backfires, It also does it when downshifting. I also noticed I can only go 45 mph in 6th gear. When I checked the spark plugs they were white on the top. I was curious if anyone could help me figure out what's the problem.


This was posted in another forum a LONG time ago and EVERYONE swears by it. It worked for me too. Here it is:

MAIN FUEL JET SIZE CHANGES NEEDED PER TYPICAL MODIFICATION:


Typical Exhaust Changes:

+2 main fuel jet size for custom 4-into-2 exhaust

or

+4 main fuel jet sizes for 4-into-1 exhaust

or

+4 main jet sizes for no muffler (open headers)


Typical Intake Changes:

+2 main fuel jet sizes for single K&N filter (inside a stock airbox)

or

+2 main fuel jet size for drilling holes in the airbox with stock filter

or

+4 main fuel jet sizes for individual pod filters (no airbox)



Additional changes:

- Add up all the main fuel jet size increases and subtract 2 sizes.

- Decrease main fuel jet size by 2 sizes per every 2000' above sea level.

- Under a mis-match condition, such as when using pod filters with a 100% stock exhaust, or 4-into-1 header with stock filter and air box, then subtract 2 main fuel jet sizes.


PILOT FUEL JET SIZES CHANGES NEEDED PER TYPICAL MODIFICATION:

Pilot fuel jet size changes are related only to the change in main fuel jet sizes according to the main fuel jet size formula described above. Note that this pilot fuel jet rule is for the main fuel jet size change BEFORE any main fuel jet altitude compensation is factored in:

Increase the pilot fuel jet size +1 for every +3 main fuel jet size increases.

Additional changes:

- Decrease pilot fuel jet size by 1 for every 6000' above sea level.



PRECAUTIONS:

- Make sure your carbs are in perfect working order before making jet changes....meaning fully cleaned internally and rebuilt, operating properly in their stock configuration, proper sized air jets and needles, etc. Otherwise, you'll like find that all of your efforts are going to be a HUGE waste of time.

- Check plug color often and adjust as needed, 2 main fuel jet sizes at a time and 1 pilot fuel jet size at a time. Bright white plug insulators are a sign of an overly lean fuel mixture condition and WILL cause damage to your engine over time, up to and including engine seizure!

- Synch the carbs after each jet change.

- Make sure the floats are set correctly

- Seriously consider purchasing a Colortune Plug Tuning kit.

- You may find it necessary to make changes to the size or shimming of the main jet needle. There are no guidelines on what or how to do these changes, this is true trial-and-error tuning!



EXAMPLE:

A 1982 XJ550RJ Seca using an aftermarket Supertrapp 4-into-1 exhaust and a single K&N air filter in the stock, unmodified airbox. Bike is primarily operated at an altitude of 2600 feet above sea level.

XJ550 Seca Stock Mikuni BS28-series Carb Jetting:

#112.5 Main Fuel Jet
#35 Pilot Fuel Jet
#70 Main Air Jet
#170 Pilot Air Jet
4GZ11 Needle


MAIN FUEL JET SIZE CALCULATIONS:

Changes made:

Exhaust:
4 into 1 with Supertrapp = +4 Sizes Main Fuel Jet

Intake:
K&N Pod Filters = +4 sizes Main Fuel Jet
Equals: +8 main fuel jet sizes above baseline
Subtract: -2 main fuel jet size per formula above
Equals: +6 main fuel jet sizes due to modifications, thus:

Stock main fuel jet size is: #112.5
+ 6 additional sizes
= a #118.5 main fuel jet size
Subtract: -2 main fuel jet sizes for Altitude of 2500' Average

= #118.5 calculated from above
-2 jet sizes for altitude adjustment

= a #116.5 main fuel jet size.


PILOT FUEL JET SIZE CALCULATIONS:

The formula is: +1 pilot jet size increase for every +3 main jet sizes increased.

Stock pilot fuel jet size is: #35
+ 2 additional jet sizes (since we went up +6 main fuel jet sizes before the altitude compensation was factored in):

= a #37 pilot fuel jet size.

Note that no altitude compensation is needed on the pilot fuel jet since our elevation is less than 6000' a-s-l.
1977 Kawasaki KZ650B
1977 Kawasaki KZ750 Twin

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Carb Issues 18 Oct 2018 08:28 #792484

  • Patton
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Kz44018 wrote: . . . Its backfiring through the carb I believe. I'm thinking of going up higher on the main jet.


Backfiring through the carb, may result from an intake valve failing to completely seal when closed, for whatever reason.

Reason can include too tight clearance, damaged valve and/or damaged seat.

Once proper clearance is assured, can perform a leak-down test to determine whether valve is completely sealing when it's closed.

A leak-down test injects air pressure through the spark plug hole to pressurize the combustion chamber.

Can perform a poor-man's leak-down test by introducing compressed air into a spark plug hole and listening to where it escapes from the combustion clamber. This may be done at TDC or any other cam positions where both valves are fully closed. Top dead center (TDC) is when the piston is at its highest position. An easy way to tell TDC is by alignment of the T mark with the case mark when viewed through the timing window.

May introduce a spurt of compressed air by using a rubber cone-tip blow gun (rubber air nozzle) held into the spark plug hole. And of course keep holding it in position to keep air from coming back out the spark plug hole while listening for escaping air at other places. The air compressor should not be running while listening because the noise will likely drown out any sound of escaping air. Or just use a portable compressed air tank.

Air heard escaping from exhaust port indicates exhaust valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from carb intake indicates intake valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from crankcase breather indicates loss of compression past rings into crankcase (perhaps worn piston rings or cylinders).

Air heard escaping from head gasket area indicates loss of compression past head gasket (perhaps due to a blown head gasket).

A leaking valve may sometimes be resolved by adjusting the clearance to within specs.

A leaking head gasket may sometimes be resolved by torquing the head fasteners when the engine is stone cold (such as after sitting overnight).

Good Fortune! :)
1973 Z1
KZ900 LTD

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