Question about MSR Whisperlite International Stove

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When changing the fuel jet the shaker needle fell out. which way does it go back in? does the sharp needle go up into the hole in the fuel jet?

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The shaker needle is inside of the shaker jet, and should be pointed up, towards the tiny hole in the shaker jet (when the the stove is set up to cook - right side up).

When the stove is cooking the needle is below the hole, and not doing anything. It is not even needed to cook.
The needle is in there so that when you carry the stove around, the stove eventually goes upside down and the needle continually pokes the jet clear. Or if it gets clogged when using, turn it upside down and shake it to do the same thing.



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Posted on May 28, 2011

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I've changed the fuel float and tap on my dragster


Hi, It sounds like you have a blockage in the fuel line or the idle jet, take off the carb again and the fuel pipe from the tank, check the tank and make sure the fuel come out with a good flow of fuel, then check the pipe, by putting it on the tank and run the fuel through make sure, if you have a fuel filter its not blocked, then take the bowl off the bottom and the float and needle out and make sure fuel comes out it should be a small stream, next take the main jet out hold it up too the light and make sure it's clear from dirt, then do the same on the pilot jet that is the smaller jet next too the main jet, the pilot jet is the one that is for your tick-over if you find its all clean then you might have turned the air-fuel mix. screw in to far, one more thing, some people forget to put the vacum pipe back on that allows the fuel to come out of the tank. if the fuel doesn't com out of the pipe or the float needle hole then see if you can get an air line and blow it backwoods and if the fuel comes out put the float needle and float back in and make sure you set the height of the float so you don't get too much or not enough fuel in the carb, good luck, MH

Sep 22, 2014 | Motorcycles

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Where does the jet that fell out when I removed the float go


When you removed the float no jet should have fallen out. If you take out the retainer pin for the float you will be removing the bowl float and needle valve. The head of the needle has a shaft that fits onto the tab of the float bowl and fits into the hole where the needle valve seat is.

Jul 31, 2013 | Briggs Stratton IC Horizontal OHV Engine ...

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Only runs with full choke, I bought the bike last week and the float needle was stuck and I think it had bad gas. so I changed the gas, cleaned the carb, reset the float needle. I also set the main slide...


Hi mate reverse the needle clip position back to factory setting this issue is pilot circuit for sure - If you have cleaned carbi you need to replace or clean the pilot jet and compress air clean the hole where the pilot jet came out of to clear the circuit. Running only with choke on is classic symptom of block pilot circuit...
Also check you fuel air mix screw this may have been altered trying to correct this issue it should be 1.5 - 2.5 turns out from fully closed..
all the change of needle position clip is doing is allowing your bike to run off the main jet (not good)
and reason for running with choke on is it is changes air fuel mix with choke on compensating for lack of fuel from the pilot jet blockage
regards Jamie

Aug 07, 2011 | 2004 Honda CRF 150 F

1 Answer

My honda engine is idling up and down


Hi and welcome to FixYa, I am Kelly
I understand this is a 2200 / 2500 W generator with an automatic idle control and that you have a 5.5 Hp GX160 engine
Perform the following:
1. Turn off the fuel selector
2. Remove the float bowl nut and bowl
3. Dump the bowl contents
4. In the threaded area where the bowl nut screws into the carb.... there is a Brass orifice. Use a thinner than usual standard screwdriver and remove the orifice / jet. As you look at the screwdriver handle inverted rotation for the jet removal will be clockwise. There s a pin hole in the orifice.... clean-out the pin hole but DO NOT poke anything into the jet hole and make it bigger. Just clean it thoroughly. Hold it up to the light and look for the pin hole after cleaning.
5. Before reinstalling the jet / orifice spray carb cleaner up into the hole your removed the jet from.
6. Also before installig the jet... briefly turn on the fuel selector and watch for fuel flow from the float needle area with the float DOWN. Gently raise the float with one finger to horizontal and make sure the fuel flow stops. Then make sure fuel flow starts again when lowered. No fuel flow here = problems from the fuel tank outlet to the fuel mainifold on the carb. (can be a clogged fuel filter if so equipped) Also some fuel selectors have a mini-bowl under them. Unscrew the mini-bowl if you have one and remove the debris. Pull the hose off the carb fuel manifold fitting and check fuel flow again by briefly turning of the fuel selector. If you have fuel here and no fuel at the float needle then the manifold is clogged and you will have to remove the float and needle then spray carb cleaner into the float needle hole watching for carb cleaner to shoot out the fuel manifold fitting.
Reassemble float and needle along with reattaching the main fuel hose to the fuel manifold fitting.
7. Reinstall the orifice / jet.
8. Reinstall the fuel float bowl and nut.
9. Fuel selector on and check for leaks.... min 1 min pause
10. TEST engine performance now.
11. If the problem persists then the most likely suspect is the automatic idle control assembly. For troubleshooting... grip the governor arm and hold it steady to see if the engine maintains a constant speed. If by holding the governor arm still you have a constant engine speed; you have a bad automatic idle control.

Unless the automatic idle control is failing....the cleaning procedure above usually brings them back to normal operation.

Thanks for choosing FixYa,
Kelly

Apr 06, 2011 | Multiquip GA25H 25kW 120V Honda GX160

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My Briggs 5550 Generator wont start. We've changed out the sparkplug, cleaned the carburetor, and drained/put in fresh gas. If I spray carb cleaner inside the carburetor behind the air filter it'll start...


You have already located the carburetor. Remove it from the engine, and take the bowl off. Inside, you will usually find two jets (small brass plugs with a hole in the center of each). Remove each one and check the hole in the center for plugging. Soak the jets in carburetor spray cleaner and blow clean. Remove the float and the needle valve that it controls. Make sure the fuel passage under the needle is free of debris. If you are careful with the bowl, you should not need any gaskets. Make sure the two jets don't change places--the holes are different size. Spray some carburetor cleaner into the jet holes. Put some fuel system cleaner (not carburetor cleaner) into the fuel tank to help clean the carburetor further. Don't leave fuel standing in the tank for long periods. Hope this helps!

Jan 19, 2011 | Garden

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I've inherited a 1985 Virago 1000 with 16000 miles on the speedo. It will only run rough with the choke on. I replaced the battery with a new one when I got the bike. Since then I cleaned the carbs,...


the carburetors will need thoroughly cleaned and related rubber vacuum and fuel hoses will need replaced. Use fuel rated hose on fuel lines.
Gasoline goes bad with time and in as little as 3-4 weeks. This effect is known as varnishing. Jets and passageways within carburetors become obstructed when varnishing occurs.
Liquid gasoline changes chemically into a gel like substance. Advanced stages of varnishing results with the solid gel changing into a crystal powder substance. Interior carb surfaces are etched in the process and may require carb replacement.
The choke and pilot circuits with most motorcycle carburetors share passageways. When pilot jets become obstructed, the choke circuit compensates and allows engine to start and idle with choke, but stalls without choke.

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FOR MORE HELP:---
Carb Cleaning 101
The elements of internal combustion engines are; correct fuel/air ratio, spark at right time, adequate cylinder compression. Motorcycle and ATV carburetors have many passageways and openings to check and clean. Subtle to radical effects on engine performance occur when jets and passageways become obstructed. Vacuum leaks and carburetor synchronization also effect performance and should be checked and adjusted. The following procedures are a helpful guideline.
Carb Cleaning 101:----Warning: Remove all rubber (Neoprene) parts before applying chemicals to carburetor parts. 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 brackets.
Air & Fuel Passageways: Trace individual fuel and air circuit passageways from beginning to end. Machines can only drill straight paths through castings to form passageways. A change of direction or angle means drilling additional connecting passageways. Access holes left by the drilling process are plugged with brass or bronze beads. Inspect and clean each passageway with spray cleaner, brushes, pipe cleaners, and compressed air. Many household items can be useful cleaning tools. Remove any discoloration and debris from carbs. Look for carb spray cleaner to exit from one or more passageways. Chase immediately with compressed air.
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 **** 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 emulsion tower (main 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.
This will help. Thanks please keep updated.please do rate the solution positively .thank you for using fixya

Apr 20, 2010 | Yamaha V Star 1100 Classic Motorcycles

1 Answer

How do I clean the carborator on my 1994 kawasaki ninja zx600-c


Carburator Theory and Tuning
carb_jet_usage1a.jpg

For some reason everyone seems to think tuning a carb is just real easy. Change a jet or two and boom, your there. Yeah, right ! There are quite literally millions and millions of jet combinations. A rough check on Bing carbs shows there are at least 13,860,000 different combinations of jets. If you are going to change carbs you'd better be prepared to spend some time and money on the job.
venturi1a.jpgmainjet_1a.jpgIf you look at a carburetor, you will notice a rather large hole going from one side to the other. This is called a Venturi. Air passes into the engine through this hole (Venturi). As the velocity of the air entering the carb (and then the engine) increases, it's pressure decreases, creating a low pressure or vacuum in the venturi. This vacuum moves around in the venturi, as the throttle is opened, and sucks gasoline through the different jets in the carb. The gas then mixes with the air going through the venturi. The way the jets are made causes the fuel to vaporize as it goes into the venturi. Where the jets are placed in the carb and where the jet's outlet is located in the venturi, determines what part of the throttle opening that jet controls. The idle jet system (comprised of pilot air jet, pilot fuel jet and pilot fuel screw) controls from 0% to about 25% of the throttle opening. The throttle valve controls 0% to 35% of the throttle opening. The needle jet and jet needle control from 15% to 80% of the throttle opening and the main jet controls 60% to 100%. This means that when you open the throttle about one eighth of the way open, all of the gas/air mixture going into your engine is controlled by the idle jet. As you can see, the different jets over lap the operating range of each other. That is, the jet needle starts to effect things before the effect of the idle jet ends. This is something to remember when working on carbs... everything is interconnected. Change one thing and it will effect other things.
OK, let's go over the different systems in the carb and see what they do.
  1. Fuel level. The fuel level is controlled by the fuel floats and the fuel float valve. The floats are hollow or made of something that will float on gasoline, such as cork. Part of the float presses against the float valve, sometimes called a needle and seat. Most times the part of the float that touches the float valve needle is bendable so you can adjust the level of the fuel in the floatbowel. All plastic floats are not adjustable. If this level is way too high, gas can leak out the carb overflow tube or into the engine. If fuel gets into the engine it will thin out the engine oil, ruining it's ability to lubricate. This will, sooner or later, blow up your engine ! If a full tank of gas in the evening turns into a half tank by morning, check your oil. If it's thin and smells like gas, change it and replace your float valve and/or check your fuel level. If the oil is OK, check under the overflow tube. If it's OK, then check where you are parking your bike 'cuse someone is walking away with your gas ! If your fuel level is just a bit high, the mixture will tend to be a bit rich. If it's low, the mixture will tend to be a bit lean. This is because a high level takes less vacuum to **** fuel into the engine and a low level takes more vacuum to do the same.


  2. Pilot or idle jet system. The idle jet controls the idle and on up to quarter throttle, give or take a bit. On some carbs, like Mikuni there is an air jet too. In conjunction with the idle jet there is an idle jet air screw. This screw leans or richens the fuel mixture for a smooth idle and on up to one quarter throttle. From the idle jet, there are little passages cast into the carb that lead to holes just in front of the throttle valve or plate. There can be just one hole or there can be several, depending on the carb design. They effect the mixture as long as the vacuum, in the venturi, is over them. As the throttle opens further, the vacuum moves to the needle jet and jet needle.
  3. The Throttle Valve. The big slide that opens and closes your throttle has a bevel angle cut in one side of the big round (can be flat, too) slide, toward the air cleaner. This angle comes in several sizes and helps control the fuel mixture from idle to about 35% open throttle.
  4. Needle Jet. This jet doesn't really even look like a jet, but it is ! It controls the fuel mixture from 15% to 60% open throttle. It sets in the center of the carb, right over the main jet.
  5. Jet Needle. This is the needle that rides in the throttle slide and goes into the needle jet. This needle controls the fuel mixture from 20% to 80% open throttle. It can come in many different sized tapers. Sometimes, one needle can have several tapers on it. The top end of the needle has grooves cut in it, usually five, and you can move the little clip on the end up or down to lean (down) or richen (up) the mixture. Most late model bikes have needles with only one groove cut in them. This is so you can't richen the mixture, thereby keeping the EPA happy.
  6. Main Jet. This jet controls the fuel mixture from 60% to 100% open throttle.

Apr 16, 2010 | 1994 kawasaki ZZR 600

1 Answer

Clogged carburator, how do I get it out to clean?


BEFORE YOU START
Make sure that dirty carbs are actually your problem. Lots of things can make a bike run poorly or not start. Weak battery, corroded electrics, old spark plugs, bad timing, low compression, mis-adjusted valves, dirty air filter, and plugged exhausts can all cause poor running. I'll write an article eventually on how to diagnose poor running conditions shortly, but for now - lets just deal with the carbs.
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 parts before you begin. These parts usually include vacuum diaphragms, needle valves, o'rings, hoses, and other parts. Spray cleaners will 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 **** 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).

Nov 24, 2009 | 2007 Yamaha V Star Classic

1 Answer

Snowmobile problem


hi jay,,if u r having to use the choke to keep it go ideling , then either u the idel jet is blocked and will give u fuel starvation ,so usin the choke the main jet has to force fuel in 2 the float chambers,, at the bottom of the carb,, so firstly remove bottoms of carbs and one jet at time take the needle jet and main out , u will see little holes on the needle jet.or needle guide jet if u like, poke a pin in the holes ,and blow threw till u see light threw them, give every thing in the bottom carb a clean while u r there, then replace that jet and everything else ,,then move to the next carb and repeat the process,,put carbs back on the bike, then air boxmake sure theres no air leaks between air box and carbs ,, try that matey,, hope it helped,,

Jan 09, 2009 | 2000 Yamaha YZF-R1

1 Answer

Re-jet the bike


than it was the day before you can actually go back to your sea level jetting a 260 main jet! If you don't rejet you can kiss your assets goodbye when you rebuild the seized engine. Air temperature makes that much difference! Our final example will deal with something often overlooked. We are still up in the hills enjoying our NEW riding area when we notice the old fuel supply getting shorter. No biggie; there's a little store/gas station just down the road. A short trip a few bucks change hands and we are ready to go again. Out on the trail the bikes are running funny sometimes pinging and running HOT. What happened?!?! When we changed jets to compensate for altitude and temperature we were still using SEA LEVEL gasoline. Gasoline sold at higher elevations have a different blend of additives to compensate for the altitude. Generally high elevation gasoline is less dense to compensate for less available air going into the engine and to aid starting. The lighter specific gravity of the high elevation fuel actually leaned out our mixture! A 1 to 2 sizes bigger main jet will get us back into the hunt. If you ride in vastly different areas try to bring enough or your normal fuel along to last the entire ride. It will save you hassles and grey hair in the long run! PILOTS NEEDLES, MAINS: So far we have only talked about main jet changes to compensate for altitude, temperature and fuel density. As most of you know there is a pile of jets in a carb. While main jets are the most critical for ensuring full power operation and engine longevity, the other jets are equally as important for a good running engine. Let's run through them quickly. Pilot jets control the low-speed and idle mixtures. Many times an adjustable jet is used in conjunction with the pilot jet. The adjustable jet allows a precise setting of the idle mixture. If the adjustable jet is located to the rear of the carb and usually on one side it is a AIR adjustment. It controls the amount of air that mixes with the fuel coming from the pilot jet. If the adjustable jet is to the front of the carb, on the side or bottom, it controls the amount of air/fuel mixture going into the engine. In either case if adjusting the mixture screw won't improve the low-end running speed it's time for a different pilot jet. Throttle valves (the slide) control the off idle, to 1-quarter open ,mixture. Some aftermarket carbs have replacement slides available with different cutaways. Changing the cutaway changes the mixture. More cutaway is lean, less cutaway is rich. Some carbs do not have different slides available, so you have to compensate by changing the mixture on the idle circuit or needle circuit. Partial throttle hesitation or rough running can be caused by the slide cutaway. Needle jets control the amount of fuel going by the needle and into the engine at low to mid throttle. There are 2 types of needle jets used in a carb. One is a primary type that has a very precise hole hole drilled through the middle of it, along it's length. The size of the hole relative to the size of the needle determines how much fuel goes into the engine. The other type of needle jet is constructed essentially the same except for a bunch of holes drilled into the side of the jet. These holes allow air to mix with the fuel before it's metered into the engine. Either type of needle jet works well in most cases but there is power to be gained on HIGH PERFORMANCE 4-STROKES by going to the needle with the holes in the side. These are called bleed type needle jets and produce more midrange power in a 4stroke. In any engine going to a leaner (smaller) needle jet is the easiest way to rejet the midrange running when going to higher elevations. Changing the needle jet leans out the mixture evenly at all the midrange throttle settings moving the needle clip doesn't. Jet needles more commonly know as the needle control the fuel mixture throughout the midrange. The shape or taper of the needle dictates how much fuel goes into the engine at a given throttle opening. The needle must work in conjunction with the fuelling requirements of the engine relative to slide position. If you have an engine with a strong hit in the midrange the needle will probable have a noticeable reduction in size the the slide is half open. Remember it takes fuel to make power and when the engine makes power it needs fuel NOW! If it doesn't get the right amount of fuel it pings or misses. You many have cleared up a little midrange pinging by moving the needle up a notch but at the same time you may have overrichened some other areas. If the problem isn't too bad you won't even notice the rich condition. If the machine stutters before it comes on the power that part of the needle's taper is too small and the only way to cure it is to get a needle with a different taper. Finding the right needle can be difficult so hopefully moving the clip will do the job. Finally the good old mainjet comes into play at 3-quarters open to full throttle conditions. Most of you already know a bigger mainjet has a bigger hole so it lets more gas into the engine! Pretty simple!! As simple as it is the mainjet is absolutely CRITICAL to high-speed engine operation. Not only does it meter the gas into the engine, it can aid in cooling the engine as well. A properly sized mainjet will let the engine make good power for a long time. A one size smaller mainjet may make greater power for a while. A slightly rich mixture burns cooler than a lean one so be sure the mainjet is big enough! One final note on jets. All of them and the carburetion functions then perform tend to overlap into some other jet's territory. If you mess with one jet, you may have to mess with a few of the others. My best advice is to not change more than one jet at a time. Slowly work out the correct jetting and keep notes on what you are doing. If you get totally fouled up at least you can go back to where you started. SIGN, SYMPTOMS AND CAUSES: How would you know if there was something wrong with your jetting? If you listen, your engine will tell you! All you need is an interpreter. Since I speak and understand several different engine dialects, I will give you a hand. Let's start with lean conditions because they can cause the most damage. In a lean condition the engine will surge and sometimes ping under acceleration. The engine will also be cold-blooded (hard to start and keep running) but will run better when hot. The spark plug will look bone white or burned in extreme cases. The engine may spit back or sneeze thought the carb once in awhile too. If the engine is running rich the throttle response will be fuzzy and not too quick. The engine will burble, miss and blow black smoke. It will start easy but will run funny when fully warmed up. The plug will be dark, wet or fouled (possible all 3!). Ok so what do you do first to cure the problem? The very first thing is to check and adjust the float level. If it's off one way or another it can throw the jetting off too. Set the float to the specs and retest the running. The next item is to determine a rich or lean condition. Let's say the engine gets hot and doesn't pull well. This is a lean condition so the engine wants more fuel. Stick in at least a two size bigger main jet and try it again. If it's better but still not right go even bigger on the jet. and try it again. Bear in mind that drastic or sudden changes in jetting usually mean an air leak has developed somewhere in the engine. Find it and FIX IT!! When the engine burbles on the top end come down 1 jet size at a time until it winds all the way down. Don't drop and more sizes! If the engine seems sluggish and lumpy or want to load up on the bottom end the mixture is TOO RICH. Adjusting the low speed mixture screw helps a little but doesn't cure the problem completely. What you need now is a new pilot jet. Go 1 size smaller and try the adjustment again. When the engine runs smooth with the adjustment screw about 1 and a half turns out from the seat you have it!! IS THAT ALL THERE IS TO JETTING??: There's a lot more to jetting than just stuffing jets in holes and hoping the problem goes away. If you can understand what your engine is trying to tell you when it runs funny you will have a better chance or correcting the problem than someone who doesn't have a clue. When you rejet, go slowly and carefully until the problem is solved. As a final thought let me remind you that jetting is a lot like life, if you have a choice it's always better to be a little rich!!,,,

Nov 10, 2008 | 2003 CCM 604 DS Dual Sport

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