posted Jan 6, 2010 10:41 AM by Doug Machan
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updated Mar 21, 2011 9:25 AM
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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.  If you look at a carburetor, you will notice a 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.
 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 float bowel. 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 suck fuel into the engine and a low level takes more vacuum to do the same. 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. 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. 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. 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. Main Jet. This jet controls the fuel mixture from 60% to 100% open throttle. We want nice clean acceleration from idle to full throttle, with no stumbling or flat spots. This can be quite a tall order if we are starting with a new carb. Actually, it can be a real challenge to get things to carburate right after something as simple as an exhaust pipe change. Now, I wish I could tell I'm the great carb man, but, well... no one has ever been dumb enough to hire me to really work over a carb. Well, there was that one time with that Kaw 650 and aftermarket pipes. It had some kind of weird stock carbs that looked like Mikunis but really were not. It had TDK or KDT or DTK, something like that, carbs. It had aftermarket exhaust pipes and was running too lean, and stumbled at one point under acceleration. Worthless pig ! The jet needles where not adjustable, so I put little washers under the needle clip, to raise the needles. The main jet only came in one size, so I drilled it out with ity-bity, expensive, jet drills. I could move the miss around, but I could not get rid of it. From the beginning I told the guy it wouldn't work and that he was wasting his money, and that at the least we needed carbs we could get parts for, but nooo. Just rise the needles, drill the jets he said... $200 later he finally gave up. I guess I shouldn't complain, I did get paid... but ! But you want to try it, don't you ? OK, the drill really isn't that hard. Simply run the engine at whatever throttle opening you want to test, for a mile or so, and look at the spark plug. Is the spark plug reading lean or rich ? Now look for the jet that controls that particular throttle opening and exchange it for a richer or leaner one. Now that doesn't sound very hard, does it ? Oh yes, the throttle transition from one jet to the next must be smooth too ! Go back over the areas that each jet controls. They overlap each other. Some a little, some a lot. Make sure you have a good selection of jets ! Most carb manufacturers have tables of specifications on the jet needles and needle jets, and other jets that you will find very useful. With these specs you can make a better guess as to what jet will work best. Some places use motorcycle dynamometers for testing. These can be a big help to get real close to the best jet setting. Working out the best main jet for a 170 MPH bike can be quite unhealthy if you only have a freeway to test on ! Just remember one thing. A dynamometer is not the real world. A fact more then one factory has found out the hard way when their super hot, dyno tested, race machines didn't run so fast in the real world, on real pavement, in real air with real bugs on the windscreen ! Anyway, what I'm trying to get over to you is that just because your buddy said he got new carb, changed a jet or two and now his bike gets 100 miles per gallon and has double the horse power, doesn't mean you can too ! It just might require a lot more work than you bargained for. Look on the bright side. Carbs used to be real simple at the turn of the century, but they didn't work as good as today's carbs. Oh, one last thing, seeing how we are talking carb theory. When an engine is cold, like when you first start it up. It doesn't evaporate the gas well. Liquid gas does not burn, so you have to put in lots of gas, because a lot of it does not vaporize. The choke helps the carb to put into the engine a very rich mixture, and at least some of that mixture will vaporize and burn. |
posted Jan 6, 2010 9:42 AM by Doug Machan
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updated Dec 28, 2010 1:36 PM
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To start any engine, Two or Four stroke, you must have Three things.- A burnable mixture of something. Gasoline, starting fluid, carb cleaner, But it must be able to burn.
- It must be compressed, that is under compression by the piston.
- There must be a way to ignite the compressed mixture at the right time.
If all three things are present, the engine MUST run. It may not run long and it may not run good, but it will run. Always remember that! The reason I say that is because engines can do funny things. Sometimes things that shouldn't work...work. Other times, things that should work...don't. We need to remember that there is a reason why it works and why it doesn't work. If you did it all right then it MUST work ! If it doesn't work...you did something wrong. When things don't work, remember these three things and go back and double check your work. In an engine these things occur as part of a cycle. That cycle is basically this: The fuel mixture must be brought into the cylinder -SUCK, compressed -SQUEEZE, ignited -BURN, and then expelled from the cylinder -BLOW. All reciprocating engines must go through these steps no matter what the design of the engine ( two-stroke, four-stroke, whatever ). In a Four-Stroke engine the intake valve opens and the piston goes down, sucking the fuel mixture into the cylinder. The intake valve then closes as the piston comes back up squeezing the mixture. Spark now occurs and the burning gases expand, pushing the piston down with lots of power. As the piston comes up again, the exhaust valve opens and the burnt gases are blown out of the engine and the process starts over again. This is all done in four strokes of the piston.In a Two-Stroke engine the piston goes down, compressing the fuel mixture under the piston and blowing it into the cylinder. As this mixture blows in it also blows the burnt exhaust gases out. The fuel mixture is blown into the cylinder through passages ( Ports ) in the cylinder walls. The piston comes up, covering the ports in the cylinder walls and compressing or squeezing the mixture. This also creates a vacuum in the crankcase under the piston, sucking the fuel mixture into the crankcase. The spark then ignites the mixture and the burning gases push the piston down, starting everything again. This is all done in two strokes of the piston.Two-Stroke
That's all there is to it. There are other engine designs but they are not used much. The rotory engine was used on several makes of motorcycle, but not many were made and they all have been gone for many years. |
posted Nov 30, 2009 8:32 AM by Doug Machan
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updated Dec 28, 2010 1:36 PM
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You will be working a lot with gasoline. Any spark, including static electricity will set it off. Plugging and unplugging electrical connections and performing electric starter tests can produce big sparks. If you light yourself off, things can be very painful indeed. A cheap fire extinguisher cure this problem and eliminates pain ! Engine backfires can also set a motorcycle air box, say like on your expensive race bike, on fire. You might find that you can almost blow out the flames, but not quite. You might find that after ten or so really big puffs of air that you are hyperventilating and getting light headed and that you are wondering whether you can get to the fire extinguisher and back before your favorite toy melts. You might, you might, yes, you might ! So you might want to put that fire extinguisher REAL close to the work at hand next time. Ah... trust me on this... You really NEED a good fire extinguisher and you NEED it close at hand !
 Safety glasses will help keep inappropriate material out of your eyes. This you will find is a very good thing ! Yes, it's just a test ride around the block, but what if the countershaft sprocket comes off and locks up the rear wheel ? Wear a helmet, leathers, gloves... just in case. Put all oily rags and paper in a metal container and keep a lid on it. This will prevent spontaneous combustion. Keep all gasoline in air tight containers which are made specifically for gasoline. This may seem simple, but far too many people are not scared of gasoline. I am terrified of the stuff. One cup of gasoline has the explosive power of two sticks of dynamite. If you leave a pan of it out uncovered the fumes can be ignited by any spark and you will not believe the fire it will start until you see it ! Special gasoline containers made with steel or thick, gas proof, plastic, are needed. No milk jugs need apply ! Clean your parts with solvent and NOT with gasoline.
 Setting up a safe shop Working on motorcycles can be dangerous, but it doesn't have to be. Common sense can go a long way to turn a major problem into a minor one. Minor cuts, if left untreated, can easily become infected and end up costing you a finger. John, the shop foreman of an auto shop I once worked at, told the story of once almost loosing a finger to a very minor cut. It got infected and puffed up like a balloon. Doctors had to cut it open and drain everything out... Yuck ! So after he told me this story, I took his advice and stopped work, washed my newly cut finger off, and put some disinfectant and a Band-Aid on it. This is what I do when I get a cut. Immediately wash with soap and water. Then rinse it with a 3% solution of Hydrogen Peroxide. Then put on some antiseptic cream and a Band-Aid. If you do this immediately, it usually does not hurt much. If you wait a while to do it, it WILL hurt. At night I leave the Band-Aid off so the wound will dry. If it gets a bit infected I squeeze the infected part with my fingers as hard as I can stand it. This sounds strange and it hurts like everything, but it seems to get rid of infected liquid in the wound and helps it heal. Put on more antiseptic cream. If it still stays infected, soak in a mixture of hot water and Epson salt. Make the water as hot as you can stand it. Again, more antiseptic cream. If it STILL stays infected, a trip to the Doctor is indicated.
| First and foremost, keep your garage floor clean! You should always have a wide, clear pathway from your walk-through door to your main garage door. Make sure you keep this pathway swept and dry. If you have a wet, greasy, or oily floor, especially on an epoxy finish, then you’re simply begging for a broken tailbone…or worse.
Next, you must have adequate lighting. There’s just no if’s, and’s, or but’s, when it comes to garage safety and adequate lighting. When you’re working on any project in your garage, always make sure you have enough room around your workbench area. If you’re cutting a long 2X4, you don’t want to pay for a new side window in your car.
Well… first and foremost a garage workbench. A good, solid garage workbench is the foundation because the rest of the work area gets built around it. Where you put your workbench is critical. If your garage is small, you have fewer options, and you should consider a relatively small workbench. If your garage is huge, then of course you have more options. Regardless of the size of your garage, the workbench should be placed in an area where it won’t affect vehicles being parked or prevent people from getting from one place to another in the garage.
Once you’ve chosen where to put your workbench, it’s time to decide what goes around it. Again, the size of your garage will play the biggest role in this decision. Every garage work area will have garage tools in it, so it’s a good time to consider some of the possibilities for tool storage. The most common solution is a tool box, followed by pegboard, shelves, then cabinets. Your own preferences take over at this point. For me, a combination of the above works well. Some folks want all garage tools in their tool box(es), while others prefer them to hang from pegboard. The point is… it’s up to you to figure out what you like or don’t like.
Having a place to design, review, stage, build, and complete your garage and home projects is a great asset for every homeowner. A garage workshop also gives you incentive to fight that ever-lurking clutter by helping you keep your garage as a place for things to happen instead of a place to pile up and stumble over stuff.
Burns come, basically, in three flavors. First degree, like a sunburn. Second degree, which produces a blister, and third degree, which is a burn that goes deep, deep into the skin. A real crispy critter. Most of your burns will, hopefully, be first and second degree. Put Ice on them as soon as you can. This cuts the pain and helps keep the blisters small. With a third degree burn, you need to see a Doctor. A burn this bad may require a skin graft. It's a good idea to keep a First Kit in your tool kit AND to use it. Even a minor cut or burn can really slow you down if you get it infected. Other things you can include in your tool kit is baking soda, water, and a good working Fire Extinguisher. If you get battery acid on you, the baking soda will neutralize it. Water will also wash acid off your warm, quivering, flesh. If you get acid on you and do nothing, the acid will give you a VERY bad chemical burn. If you have water and baking soda the problem, and the pain, disappears.
Lastly, start thinking about what you are doing. If you are really pushing hard on that screw driver, and it slips off the screw, where will it go ? Into the work bench, or into you hand ? When you really pull on that wrench and it slips off the bolt. Where will your knuckles go ? Into something hard and sharp ? Try to think ahead. Pain hurts, so avoid it. One more thing. Being a Macho Man or Women will NOT stop a piece of wire, from the wire brush wheel on you bench grinder, from ramming into your eye. Be a pansy, wear safety glasses, helmets, gloves, and use safety equipment. Like I always say,"If you don't, It's OK... I don't care, it's not my body, and it won't HURT me at all !"
Feel Free to post up more tips that will help your fellow racer be safe. |
posted Nov 17, 2009 9:19 AM by Doug Machan
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updated Dec 28, 2010 1:41 PM
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SPARK PLUGS Spark plugs....We can make this easy or we can make it hard. Let's start with easy. After running for a while normally, stop the bike and take the spark plugs out. They should look a light chocolate brown in color. If , black and sooty the engine is running too rich in the fuel departement or too cold of spark plug. If black and shiny (oily) they are oil fouled. If they are whitish you are running too lean a fuel mixture and/or wrong ignition timing or too hot of spark plug. When you see this, your engine is about to blow up!!! Now the harder stuff. A spark plug does not make your engine run hotter or colder. The terms hot or cold refer to the temperature of the tip of the spark plug itself. The plug must keep a temperature of, between 752 and 1652 degrees Fahrenheit. If it gets too hot it can fire off the air/fuel mixture at the wrong time. This can cause detonation and/or pinging which will put a hole in your piston... not good. If it gets too cold it will not burn off the carbon and fuel deposits on it's tip and the plug will foul out (stop working) not good either. The heat range of a spark plug is controled by the length of the center electrode. A longer one is hotter because it takes longer for the heat to flow through it to the cylinder head. As you might think the cooler plug has a short center electrode. To get a true plug color reading you must run the engine,on a level road, at the throttle setting that you want to test, for about a mile, then kill the ignition, pull the clutch in and coast to a stop. Then pull the plug and look at it. This could be a real thrill on most of the newer street bikes. As the engine ages and more oil gets past the rings a hotter plug may be in order. If you ride at low speeds all the time a hotter plug will keep the plugs from fouling. If high speeds are your thing, a cooler plug may be just the ticket. Don't be afraid to pull that plug out and give 'er a read! If you would like to see more Spark Plug Images... 29 to be exact.  Oil fouled | Oil Fouled | Carbon fouled | Too Cold | To Cold | Cold or Rich But OK | Cold or Rich But OK | Cold or Rich But OK | Good | Good | 
Good | Good | Real Good | The Best | Best | 
Best | Best | Good | Good | Good | Kinda Hot | Hot or Lean But OK? | Hot or Lean But OK? | Hot or Lean But OK? | Too Hot or Lean Pre-ignition Range | Too Hot or Lean Pre-Ignition Range | Too Hot or Lean Pre-Ignition Range | Too Hot or Lean Pre-Ignition Range | Too Hot or Lean Pre-Ignition Range | |
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posted Nov 17, 2009 7:34 AM by Doug Machan
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updated Mar 21, 2011 9:29 AM
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Drum Brakes are used mostly on the rear wheel these days. If you are working on early 1980s, or earlier, you will find them on the front wheel too. They come in two general types. Single Leading Shoe and Twin ( Dual ) Leading Shoe.
The Single Leading Shoe has a cam which pushes one side of each brake shoe out to make contact with the brake drum, when the brakes are activated.
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The Twin Leading Shoe has two cams on each end of the brake shoe pushing both ends out to meet the drum. This gives better shoe to drum contact, increasing braking power. They are, however, more difficult to adjust and if not adjusted right, give less braking power than Single Leading Shoe types. |
Most motorcycle brakes die from abuse not wear. The brake cam shaft rusts up tight and/or the glue holding the linning to the shoe fails. In both cases you will need to remove the wheel, remove the brake shoes and drive out the brake cam and clean it.
To replace the Brake shoes simply lever one up and they both will pop off, but still be connected by the springs. Switch the springs to the new set of shoes and lever them back on. If they still have thick, within spec, linings, sand the glaze off with sand paper and reuse them. Do not breath any of the brake dust. Clean up the brake backing plate, grease the brake cam shaft and pivot post. Then put it back together. Take some sand paper and sand the inside of the brake drum. Again, don't breath the dust. Very probably it will have some wear and/or grooves in it. It should be turned down to give the best braking, however this takes special equipment and can be expensive. Most times, just sand it as smooth as you can and things will work just fine.
Front Drum Brakes are normally cable operated. You need to adjust the connector between the two Brake Cam Levers (arms) so that both ends of each shoe contacts the brake drum at the same time. To do this, loosen both the cable adjuster and the rod connecting the two brake cam levers. Tighten the cable adjuster. The one on the brake drum, not the one on the handlebar. When the brake starts to drag, keep turning the wheel and get a good " feel " of how much drag there is. Now tighten the rod going to the other brake cam lever till the drag " feels " about twice as much as before. Tighten the lock nut, then adjust the cable so that there is at least an 1/8" of play at the handlebar brake lever. By adjusting the play you can make the brake lever engage the brake wherever you like. Like closer to the handlebar if you have small hands. Don't be afraid to make the lever fit your hand. Just make sure there is enough free play in the cable so the brakes don't drag, and that the lever does not touch the handlebar when they are full on. How do you tell if they are dragging ? Feel the drum after riding a ways. If it is really hot and you have not used the brakes much, they are dragging. If you are sure the brakes are not dragging and the drum is still hot, check your wheel bearings.
Rear Brakes can be cable or shaft operated. They need about 1/2" of play. Normally, they are adjusted by a nut or wing nut on the rear end of the cable or rod that is actvated by the Rear brake Pedel. Most, if not all, are of the Single Leading Shoe type. Repair them just like the Front Brakes.
When everything is back together, but before you tighten the axle, spin the wheel and put on the brake hard and hold it. Then, still holding the brake on, tighten the axle. This aligns the brake shoes and drum, making the brake work better. Do this for both Front and Back Drum Brakes, Single or Twin Leading Shoe. (click on images to get full size)
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