82LTD 750 Carburetor Slow Gas Leak

[calf82LTD]

Hello, I have a '82 Kaw 750 LTD bike runs great and I love it, but recently I have notice that a carburetor on the choke side is leaking gas. I have read through the service book and appears it may have something to do w/ the float valve??? I was also thinking maybe the O-ring has gone bad on that float bowl?? Does anyone have any suggestions? Is this a relatively easy problem to fix?

[MFolks]

Carb Cleaning 101
Written by MShively
Tuesday, 06 February 2007


The elements of internal combustion engines are: correct fuel/air ratio, spark at right time, adequate cylinder compression.

There are many passageways and openings to check and clean. All are important in function and when obstructed or not working properly, have subtle to radical effects on engine performance. Vacuum leaks and carburetor synchronization also effect performance and should be inspected and adjusted following the below procedures.

Carb Cleaning 101
Warning: Remove all rubber (Neoprene) parts before you begin. These parts usually include vacuum diaphragms, needle valves, o’rings, hoses, and other parts. Spray cleaners may damage these parts. Do not disassemble individual carbs from the carb bracket.

Air & Fuel Passageways: Trace and learn individual fuel and air circuits from beginning to end. Machines can only drill straight through the cast passageways. To change direction, another angled passageway must be drilled. The union is plugged with a brass or bronze bead. Inspect and clean each passageway with spray cleaner, brushes/pipe cleaners/etc, and compressed air. Remove any discoloration and debris. Look for spray cleaner to exit from one or more passageways.

Jet Cleaning: Inspect jets by holding to light and look through them. You should see an unobstructed round hole. Clean the jets with one or more of the following: jet cleaning wires, soak solutions, carb spray cleaners and compressed air. Re-inspect jets after cleaning and install when clear of obstructions. Some main jets have paper-like gaskets. Most have metal spacers between the jet and the emulsion tube. Some screw directly into a brass emulsion tube which is machined for a 7mm wrench at its float chamber exposed base.

Inlet Fuel Valve: Inspect the needle valve & spring. Press down the tiny metal rod that protrudes from the butt or float end of the needle valve. The spring should move freely and return the rod to its location. Check the needle valve’s seat area for a groove or other wear. It should appear highly polished. Some needle valve seats are rubber and wear may not be visible. Inspect the needle valve jet seat. You can clean the jet seat with Q-tips and semi-chrome polish if necessary.

Carb Body Castings: Blow air through the atmospheric vent holes located on the dome of each float bowl chamber. Air should exit via hoses or brass nipples. Inspect the emulsion tubes and passageways (cast towers that jets thread into) for discoloration and debris. Clean interior emulsion towers with a soft bristle gun cleaning brush. Clean each Venturi (main carb bore).

Needle Jets & Jet Needles: Clean the needle jets, jet needles, and passageway or tower that needle jet screws into. Clean the emulsion tube (pipe between needle jet and main jet) (Main Jet may screw into emulsion tube). Jet needles are part of the throttle slides. See below…

Throttle Slides: There are several types of throttle slides: Mechanical linkage, vacuum, diaphragm, and cable. Disassembling the jet needle from the slide is not always required for cleaning. If you have vacuum piston type throttle slides (large diameter solid metal slide), avoid cleaning the lubrication from sides and caps. If piston type check cap vents and passageways with air. Clean if necessary and re-lube. If you have rubber vacuum throttle diaphragms, inspect for dry-rot, defects, and tears by gently stretching rubber away from center. Do this until all areas around diaphragm have been inspected. Replace any defective part as described above. Clean carb body areas around diaphragm including air passageways and air jets. Diaphragms have a locator loop or tab fabricated into their sealing edge. Observe this locator upon reassembly. Avoid pinching the diaphragm when reinstalling caps.

Fuel Screws: Fuel screws have sharp tapered ends. Carefully turn one fuel screw in while counting the turns until it seats lightly. Warning: These screws are very easily damaged if over tightened into their seats. Record amount of "turns-in" and remove the fuel screw, spring, washer, and o'ring. The fuel screw is part of the enrichment (choke) circuit...clean passageways as described above. When carbs are assembled, spray low PSI compressed air into diaphragm air vents located at intake side of carbs. Throttle slides should rise, then fall when air is removed. Lightly lube external moving linkages. Reinstall carbs and follow through with carburetor synchronization.

Throttle Cables: Lubricate cables periodically. If cables are disconnected from carbs or removed for replacement, etc . . . remember cable routing and ensure proper reinstallation routing. Avoid bread-tying, sharp bends, and pinching cables. Adjust cables so throttle grip has about 5mm of play or throttle slides or butterfly valves may not open completely (full throttle)(wide full open).

Float Bowls: Inspect float bowls for sediment, gum or varnish, crystallization, and defects. Clean all pipes, tubes, passageways, and embedded jets with cleaners and compressed air. Remove and clean the drain screw and area. Inspect bowl gasket and replace if necessary. Clean and inspect overflow pipes and tubes, look for vertical cracks.

Floats: There are several types of float materials: plastic, brass, black composite, tin, and others. Handle floats carefully. Avoid bending, twisting, denting, or other means of mishandling. Most floats are adjustable by bending a small metal tab near the float axle end. Do not change the float adjuster tab unless tuning fuel service levels. Clean metal floats by soaking or by spraying cleaner and wiping clean. Other material type floats may require replacement if cleaning is necessary. Inspect the needle valve (float valve) and seat. Check needle valve’s spring loaded pin. It should depress and return smoothly and without resistance. Check the needle valve’s tip for a worn groove. Replace needle valve and seat if either symptom exists. These parts wear together and must be replaced as a set.

Synchronization: This is a fine adjustment performed usually and preferably with the carbs installed and the engine running. The unusual part is performed with gauged wire with the carbs on the work bench. Carburetor synchronizing balances Venturi vacuum at the exhaust side of each carburetor, resulting with smooth idling and optimized performance at all throttle openings. Synchronization is checked using a set of gauges which are either air vacuum type or liquid mercury type. The gauges are connected to vacuum ports on the intake manifolds via nipple tubes or if sealed with screws, sync gauge adapters will be needed. With the engine running at temperature, and with a fan or means of forced convection aimed onto the engine, the carbs fuel screws and idle are adjusted, then the synchronization is adjusted via adjustment screws on the carbs. A reserve fuel tank is recommended for convenience of accessing carbs during this procedure. See gauge instructions and repair manuals for detailed use of synchronization gauges.

Notes: While carbs are apart, record the jet sizes. Look for a very small number imprinted on the body of the jets. Verify that numbers are the same for all jets on models with in-line cylinders. A few transverse-4 models and V-engines, the inner and outer carbs use some different size jets and it's important to not mix them up. If you have dial or veneer calipers, measure and record float heights. Perform measurements with floats just touching needle valves, though not depressing the needle valve rods. Replace fuel and vacuum hoses. Be sure to use fuel rated hose for fuel. Install or replace in-line fuel filters. It’s a good time to remove and clean interior petcock fuel filters. Inspect carb manifolds for dry-rotting, inspect all clamps and air ducts. Inspect, clean, lube, and/or replace air filter(s).

[antiq]

That was a very long and very informative reply. Short version- Run some carb/injector cleaner with the fuel for the next few fillups. Should solve the problem. If not the it's probably time for a new float valve needle and seat.

[MFolks]

Yes I know, I copied it from the website KZrider.com - Home

[calf82LTD]

Thanks for the help, is replacing float valve needle & seat difficult? Is something I could do (I am a relatiove novice) or something a mechanic shoudl handle considering my experience level?

[MFolks]

You will need metric sockets, small needlenose pliers,something to sit on close to the ground,possibly an offset phillips screwdriver, a well lit working area, and it's not something to be rushed.

Yes, you can have a shop do it for $$$$, but what better way to learn about the parts on your bike than doing the maintenance yourself? Have you changed the oil,sparkplugs,done a carb sync or checked the valve clearance? All these can be done without going to a shop.

[calf82LTD]

Yes I routinely change my oil, I have also changed spark plugs, air filter, tach lines etc. Can I do this w/ the carbs still on the bike? Will there be any specific setting that need applied? Also in your opinion is it safe to ride the bike until I can get to the problem?

Thanks for all your help

[vinnye]

Calf, I dont know if you have a 4 cylinder Ltd or a Twin?
I have worked - albeit a long time ago on the 4 and found that taking the carbs off the bike was the easiest way to do this sort of task.
However, it should be noted that with age hardening of the air intake rubbers that connect the carbs to the airbox, removal and worse installation can be a pain!
If your rubbers are still quite pliable - you should be OK to remove the carbs.
If not, see if you can find a replacement set - it will be worth it if you have to get the carbs off.

[calf82LTD]

I have a 4, I was hoping to avoid taking the carbs off, mainly because this problem is linked to one carb & it is easily accessible.

My Clymer manual mentions gently tapping the top of the carb to "jiggle" loose any dirt. Has anyone tryed this successfully? Also someone has suggested running some carb cleaner through, I can hestitate to do this because I dont want to drive it w/ a fuel leak

[vinnye]

If its one of your outside carbs, you may be lucky.
With your bike on the main / centre stand ;
You could get a piece of clear plastic tubing and push it onto the drain plug and bend it up alogside your carb. You could attach it with a tie wrap or piece of string - so that you have both hands free.
With the pipe on, crack open the drain plug screw and see how far up the tube the petrol goes - it will give you an idea of the float height for that carb. If the float is stuck - a tap may free it off for you.:0

you could also at he same time run gas through the drain into a clear container to see if there is any debris . dis-colouration?
This may allow you to run a carb cleaner solution through at the same time?

You may also have enough clearance when you have taken the tank off to remove the 4 screws holding the top cover on the carb. This will allow you to remove the diaphragm and needle valve. It is often a needle vale not seating correctly that allows gas to overfill the carb. (There is also a pet **** problem at ther same time! If the tap was stopping gas except when the vac from the engine allows it to, then a stuck valve would not have enough gas to overfill the carb.)

Hope this helps.

[antiq]

Originally Posted by calf82LTD

I have a 4, I was hoping to avoid taking the carbs off, mainly because this problem is linked to one carb & it is easily accessible.

My Clymer manual mentions gently tapping the top of the carb to "jiggle" loose any dirt. Has anyone tryed this successfully? Also someone has suggested running some carb cleaner through, I can hestitate to do this because I dont want to drive it w/ a fuel leak

It's worked many times for me. I used a screwdriver handle and tap it on the heavy portion just above the float bowl.