The Keihin FCR Carb With Zip-Ty Racing - Dr. Dirt

writer: Karel Kramer
photographer: Karel Kramer

Tech How-To
A good portion of modern four-stroke engine performance is due to the Keihin FCR arburetor. An accelerator pump and a high-tech slide supported by four wheels make the FCR a relatively complex design. There are many parts that can wear out and get dirty or gummed up. There are a few shops that specialize in mods and service for these carburetors. Some, such as JDJetting (www.jdjetting.com; 253.939.7114) and Factory Pro (www.factorypro.com; 800.869.0497), sell kits that you install yourself, and others, such as Zip-Ty Racing (www.ziptyracing.com; 760.244.7028) and Tokyomods (www.tokyomods.com; 888.457.9403), will set up the carburetor for you or actually modify it for increased performance and response. White Brothers offers both options.

As complex as the FCR carburetor is, it is more intimidating to look at than it is to work on. You will still need a good manual.

Getting the carburetor off and back on will be the hardest part. You'll need to remove the cover on the side of the carburetor, disconnect the throttle cables, make sure the vent hoses are all free from the bike and disconnect the wire to the TPS. Do not remove the TPS from the carburetor; it is synched to the throttle shaft with a meter, and it must be resynched if removed. With perimeter-frame machines, it is almost always easier to take off the subframe and the shock before removing the carburetor.

01 Ty Davis starts by thoroughly cleaning the FCR body in a solvent tank filled with Simple Green rather than using a petroleum-based solvent or contact cleaner. He warns that you should never spray contact cleaner into the mouth of a carb

02 If you have an aftermarket fuel screw installed, this is a good time to remove it. Take care so you don't lose the small spring, washer or O-ring. If you still have the stock fuel screw, removing it can wait.

 

03 You will need to extract this bolt from the throttle linkage above the slide. It may be a secure Torx with a tiny post in the middle. You may need to visit a special tool store to find a dimpled Torx socket.

04 With the Torx removed, the slide's lifting arm can rotate out of the way, and the slide can be pulled out. The brass fitting on top of the slide holds the needle in place.

05 The slide has a wear plate that lifts off. Some companies recommend changing it every 25 hours. It is an expensive part, but replacing it can make a big difference in how crisply and cleanly the bike runs down low.

06 The back side of the wear plate has this very delicate seal. Davis warns that chemicals like contact cleaner will cause the seal to swell and ruin it. It is a good idea to replace the seal when the carb is apart.

07 Davis removes all the vent hoses at this point. Small brackets mounted on each rear corner of the float bowl guide some of the vent hoses. Remove the bowl screws and the idle adjustment bracket.

08 Work off the float bowl and look for any dirt or other junk in the bowl. This one is quite clean. Most water and sediment will settle in the drain bolt.

09 With the bolt removed, the throttle pivot shaft should simply pull out. Note the return spring attachment and the placement of the two washers. Clean up the shaft and assorted parts. Set these parts safely aside.

10 At the top of the slide will be some arrangement that allows removal of the needle. Some off-road bikes have nonadjustable needles (only one clip position), and they can be replaced with an adjustable one for tuning.

11 Using a small tool, push out the float pin. A small Allen wrench or the back end of a drill bit should work fine. Once the pin is moved, you should be able to pull it out with your fingers.

12 The float manipulates this float needle to keep the fuel level in the float bowl constant. Look for damage near the pointed rubber tip. The needle is loosely attached to the float via the wire loop. Don't lose it.

13 The main jet is threaded into the needle jet, so remove them together. The fuel baffle (called a "spacer" in the manual) will come off easily after the needle jet tube is out.

14 Unscrew the starter jet and the pilot jet. A blade screwdriver with a tip or shaft larger than 4mm wide will jam in the pilot-jet opening. Clean all the jets, and ensure that all of the openings are unrestricted.

15 There is a screen at the bottom of the needle-valve seat that prevents trash in the fuel from entering the float bowl. It cannot be removed for cleaning, so use compressed air to blow it clean from this side.

16 Use a finger to operate the accelerator-pump rod through a full stroke. You should feel spring resistance but no hard spots or hitches in the travel. If it doesn't move freely, pull it apart and clean it.

17 A small screw holds the fuel-line fitting in place. The carburetor was otherwise quite clean, but this fitting and passage need a bath.

18 A little grease on the O-rings will ease the cleaned fitting back into the carburetor body. Don't get carried away with the grease. Install the screw that holds the fuel-line fitting. It shouldn't need thread-locker.

19 The throttle shaft rides on two small needle bearings, and they should get a little grease before the shaft is installed. A cotton swab is a good tool for this job.

20 The throttle-return spring has a hook that must engage the throttle shaft before the shaft is reinserted. The shaft washers fit between the body and the throttle-valve lever: the metal one against the carburetor body and the resin washer against the lever.

21 Getting all the throttle-valve parts lined up takes a bit of fiddling, but once they are arranged, the throttle shaft should easily slip through the freshly greased bearings.

22 After setting the plastic spacer in place, use a socket to thread the needle jet/main jet combo into the body. The pilot and starter jets go in next. The threads are brass inside aluminum, so don't go crazy tightening jets.

23 Before the float and needle valve go in, this wire loop attached to the needle must be slipped over this tang on the float. Work over a surface that will allow you to find the float needle if it is dropped.

24 Lower the float and needle valve together. Carefully guide the needle valve into the needle-valve seat. If the tip of the needle bumps the seat, it will pop the wire loop off of the float and cause needless cursing.

25 The manual outlines a method for setting the float height using a caliper. Davis uses a Honda tool that measures the height of the float while lightly blowing into the fuel line.

26 Lift the throttle-slide lever arm out of the way with one hand, and hold the slide (throttle valve) and the throttle-valve plate together with the other hand. Make sure the needle doesn't hang up while going in.

27 The bolt holding the lever arm to the throttle shaft is the only one in the carburetor that calls for thread-locker (blue). Again, you may need a special Torx bit that is drilled to clear the center post.

28 Insert the front float-bowl screws and snug them down, but remember to add the vent hose guides. Then attach and tighten the idle-adjustment screw and bracket.

29 Using your good #2 Phillips, take out the three small screws holding the accelerator-pump diaphragm in place. Detach the cover carefully so you don't lose the spring that rests on the diaphragm.

30 Early FCR carburetors had much poorer accelerator-pump sealing, and the pump membrane could pack with dirt. You can see that only a little dirt has entered this pump and the membrane is in good condition.

31 Replace the diaphragm, spring and cover; tighten the screws; then move to the top of the carburetor body and replace the top. On a Honda, this wire holder goes on the front screw.

32 Before installing the fuel screw in the carburetor body, first slip the spring over the end of the fuel screw, followed by the washer and the O-ring. This Zip-Ty screw comes with the new parts. The rubber covers are separate.

33 With a stock or aftermarket fuel screw, it should take between eight and nine rotations to fully tighten. If you get less than eight turns, don't force it. Check the threads on the screw and in the carburetor body.

34 The stock hot-start fitting has a plastic 14mm hex that is a pain to get a wrench on. Zip-Ty Racing sells a billet-aluminum unit with a 10mm hex. If you haven't already, remove the hot-start plunger and check for corrosion.

35 Zip-Ty Racing also makes a float-bowl drain bolt with a magnet in it. We've tried them, and the magnet nearly always has metal stuck to it. Now install the drain bolt (stock or aftermarket).

36 All that is left is to reattach the vent hoses neatly, and the carburetor is ready to go back on the bike. Now just keep it this clean, and your engine will stay very happy.

How to Work the System 4 stroke engine

Why is called a 4 stroke engine, because there are four steps. Here are the details of each process. To make it easy, then your email settings to HTML, so images will appear sequentially. Images taken from the website www.howstuffworks.com / engine.htm. On this website, the image seen moving. But for the sake of simplicity, the picture intentionally set of steps.
1. Intake Called the intake step because the first step is to suck through the piston from the carburetor. Fuel supply is not enough just from the spray carburetor. The way it works is as follows. First piston at the top position (or called Dead Spot On). Then the piston to suck the fuel that already gives a chance / mixed between gasoline and air in the carburetor. The piston then retreated to suck fuel. To open, the necessary valve or inlet valve that will open when the piston down / sucked downward.
Movement is governed by the inlet valve or a mechanical camshaft. Namely, camshaft valves regulate the amount of opening by pressing a lever valve. Own camshaft driven by keteng chain which is connected between the camshaft to the crankshaft. For details, see the following figure.

Notice that A is the Intake Valve (valve into the fuel) and the valve is pressed (opening) because I (camshaft), pressing the valve A. Thus, when the piston descends, then A is open at the same time the fuel drawn into the combustion chamber. A will cover a certain extent before the second step: compression. Keteng chain is not visible because it will be difficult pictured above, but the crankshaft (P) is connected with the camshaft (I). Some European cars like Mercedes use the chain as a liaison between the crankshaft and camshaft, but mostly in Japanese cars use belts that we know as the timing belt.
2. Compression This step is a continuation of the steps above. After the piston reaches the lowest point in the phase of intake, and intake valve is closed, and the compression process. Namely, the existing fuel in the combustion chamber is compressed. The room was shut tight because the two valves (intake and exhaust) is closed. This process continued until the bursting of the following steps in step 3 spark plugs.

3. Combustion (Combustion)
The following stage is the spark plug at some point it will explode after PISTON STOP MOVING OFF TO ACHIEVE AND REVERSE A FEW DEGREES. So, do not explode when the spark plug piston at top point (called a point of 0 degrees), but the piston back up, just exploded. This is because to avoid the energy wasted because when the piston at top dead point, there is still latent energy (that is saved due to urge the compression process). If at the point of 0 degrees spark to explode, could be the piston back but mengengkol crankshaft to the rear (the motor backwards, not turn the wheel to the front).
After the burning process, the piston has the energy to push the crankshaft which will be channeled through the gearbox and the sprocket, chain, and lastly to the wheels.
4. Exhaust (Disposal)
The last step is done after burning. Due to the combustion piston is pushed down to the lowest point, or is called Bottom Dead Point. After that, the piston will be pushed to the front and exhaust valve open while the intake valve is closed. Therefore, the exhaust gas is pushed into the exhaust port hole (or we say the connection to the exhaust hole). Thus, we can discard all the rest of the exhaust gas due to combustion. And after the net again, and then we'll go back to repeat step 1 again.

Tech Tips to Keep Your Bike Running Strong

With Pro Circuit's Dave Chase.



Today's bikes aren't cheap, so getting your money's worth out of your bike is critical to your enjoyment of the sport. It's possible to offset the cost of riding and greatly extend the life of your bike if you keep up the necessary routine maintenance. There are many little chores that are easily neglected; such things as lubing the cables after you wash your bike or tightening the spokes properly can allow your bike to not only last longer but to operate better. Some of these tech tips may seem simple, but we feel these seven areas are often overlooked—and have the most potential to save you money in the long run. So we caught up with Pro Circuit's ace wrench Dave Chase and asked him about routine maintenance.

Chase is an experienced mechanic and fabricator, with off-road and motocross credentials. Plus, earlier in his career he earned the S No. 1 plate by making fragile Husqvarnas survive distance races. He's worked with budgets of all sizes, so he was the ideal source for information. Here's what he said about exhaust-pipe maintenance, carburetor care, spoke maintenance and tightening procedures, proper chain treatment, the cleaning and lubing of cables, diagnosing reed-petal problems and doing a "quick fix" at the track should you break or crack plastic parts on your bike.

Cleaning and Lubing Cables



Lubing your cables is one of the cheapest ways to keep your bike feeling new. Water and dirt seep into your cables when you wash the bike. Using a pressure washer is even more of a problem. Cleaning and lubing your cables not only eliminates the water and dirt but also increases the cable's life. To clean and lube your cables, you have to remove the cable from the perch and lever. For throttle cables you must disconnect the carburetor end; you don't want to flush water and dirt into the carburetor.Put on a standard cable lube tool and flush the cable with contact cleaner. The contact cleaner will cleanse any dirt and grime in its path. Then flush the cable several times with a lubricant.

About every third time you lube the cable, reassemble the lever with some light grease around the pivot hole. The light grease will give the lever a smoother feel and reduce the effort required to operate it. The grease will also attract grit, so you will need to clean the lever and perch more often than if you leave it dry.

You must remove the cable from the control end
(both ends on the throttle cable)to lube it.



Motion Pro and some of the manufacturers sell
these little cable pressure devices.



The lube tool is sealed with rubber,
but the spray will leak, so use a rag to save the mess.

Pipe Maintenance



Plated pipes can be cleaned with any bike washing product, but raw steel pipes need Scotch-Brite. When installing your exhaust system, you should remember the seal between the cylinder and the exhaust spigot is crucial to your bike's performance. On a two-stroke, whenever you remove the pipe, the rubber O-ring (or crush gasket on some Hondas) should always be inspected for any cracks or blemishes. Even if it just has a flattened look to the outside, replace it. Some bikes have a thin metal ring that goes into the exhaust port to prevent the steel pipe from damaging the aluminum surface the pipe butts up against. Make sure this ring is still in place and in good condition. If new O-rings don't make a tight fit, you may need to use a thin coat of high-temp silicone to get a secure seal.

Install all pipe springs before you bolt the exhaust into place. This will allow the pipe to get the best seal with no binding. Installing the springs first will allow the somewhat-delicate vibration-canceling rubber mounts to do their job without being torn in half. After every wash, scrub the entire surface of bare steel pipes with a Scotch-Brite pad and some cleaner. Scrubbing will rid your pipe of any corrosion and make it look new again. If you have a four-stroke, you should always wipe down the header with a Scotch-Brite pad. Keeping the surface looking like new will ultimately make it last longer.

Cleaning a four-stroke header will prolong
the life of the part and keep it looking nice.



Keep the O-rings or gasket that seal the pipe to
the cylinder joint fresh and tight for best performance.



Exhaust pipe springs should be kept new and tight as well.
They age like any other part.

Chain and Sprocket Care



The key to good chain life is always having your chain adjusted properly and keeping it lubed. Whenever you install a new chain, you must replace the sprockets. When you have a new chain and new sprockets, they wear together. Replacing the whole drivetrain also allows you to get the most out of your chain and sprockets. Putting a new chain on a worn-out sprocket will wear out the chain immediately. Similarly, a worn chain will ruin new sprockets. For all but the most-serious 125cc-class racers, replacing the standard chain with an O-ring chain will save a great deal of money. An O-ring chain lasts much longer, so it doesn't wear out sprockets as quickly.

Whenever you install a new chain, make sure the master-link clip opening is facing the opposite way of the travel, so there is no chance of the clip hitting something and getting knocked off. If you ride in any mud, watch to see that the master-link clip doesn't get worn. The clip can wear so thin it breaks! Always make sure your chain is adjusted correctly and is lubed every time you head to the track. The best time to lube your chain at the track is right after you pull off. When the chain is still hot, it will allow the lube to flow inside the rollers and pins where it is needed most.

Make sure that the closed end of the master link
clip faces forward so it doesn't get knocked off.



He sprocket bolts must be tight or the hub will be ruined.
Many mechanics suggest using new bolts.

Spoke Maintenance and Tightening



There is a definite science to tightening spokes; you can't just crank them tight with a spoke wrench and call it good. When tightening spokes, always space out the tightening, skipping five spokes at a time. It will take about seven wheel rotations to tighten every spoke. Skipping those five spokes allows them to be tightened evenly; you won't be pulling one side of the wheel more than the other.

When tightening, go a quarter turn at a time with your spoke wrench to avoid pulling the wheel out of true. If any spokes are loose but the nipples are hard to turn, give them a drop of assembly lube or motor oil so they turn with more ease.

You can buy this small lube bottle at a hardware store.
Aerosols are too much for this job.



A small amount of lubrication (light motor oil)
will keep the nipples from corroding to the spokes.



Use a spoke wrench with a snug fit on the nipple,
and tighten a little at a time.

Carburetor Care and Maintenance



Four-stroke and two-stroke carburetors are very similar in that they both require general maintenance on occasion. If the bike sits for a while, gas will evaporate and leave a dry, powdery or sticky buildup in the carburetor. The residue may plug all the jets, but almost certainly it will block the pilot jet. Ideally, you should drain the float bowl after riding and store your bike with its fuel petcock turned off. If you fail to take those steps, it's important to disassemble the carburetor if your motorcycle hasn't been ridden in a while. Some of today's fuels can go bad in just a month.

On four-strokes you also have to take apart and lube the hot-start cable just as you do with all your other cables. When you wash your bike, water runs down the cable, gets into the hot-start mechanism and causes corrosion in the carburetor. If the hot-start mechanism corrodes badly, it could demand a new carburetor body.

Check your float level based on what the owner's manual says. The floats can come out of adjustment over time and with extreme use. The carburetor is the heart of your bike, and it should be serviced and cleaned on a regular basis.

Use a Phillps screwdriver with a good tip
that fits the carburetor float bowl screws well.



Clean inside the float bowl, then disassemble and
clean the accelerator pump on the bowl's bottom.



You adjust the float level by bending the small
tang that depresses the float needle valve.

Emergency Plastic Repairs



Drill small, paired holes along both sides of the crack that needs repair. If you break a fender or a shroud while at the track, there are quick and dirty ways to repair the crack or break so you can finish your ride. You can stitch up your plastic just as a doctor would stitch up a cut. Just drill a few holes on both sides of the crack and run a few zip-ties across. Also, you must drill a hole at the end of the crack so the crack doesn't continue. Don't space the holes more than 1/2 inch apart. It may not be the prettiest way of repairing your bike, but when you're out at the track, it's an easy fix and it really works!

Make sure there are sufficient holes
for the repair to have strength.



Use plastic zip-ties or safety
wire to "sew" the repair together.



The temporary repair isn't
pretty but it amazingly effective.

Reed Maintenance



When your bike becomes hard to start or won't carburet cleanly at small throttle openings, you should begin to suspect your bike has a reed problem. When you pull out the reed cage, look at the outer corners of the reed petals. Usually, the first area to wear is the outer corners, which will chip or fray. Any chipping or fraying will keep the reed from sealing completely. Whenever you see any damage or wear to the reed edges, you must replace the reed petals. Simply remove the screws that hold the petal in place and install a new one.

Use a quality screwdriver, since the screws are often sealed in place with a thread-locking compound. Plus, the heads are tiny, and you don't want to risk stripping them. When you install the new petal, make sure it is indexed properly. Simply match it up with the shape of the cage and the petal stop. When you screw the petal back into place, be sure to use a thread-locking agent on the screws so they have no chance of backing out; digesting a reed-petal screw is bad news for a two-stroke engine. Also, make sure you use a fresh gasket (if any) when you put the reed cage back in the motor.

Reeds usually install only one way.
Note that one corner is round and the other angled.



Reeds tend to show wear at the tips and front corners.
They can fray or even chip.



Use Loctite on the screws that hold the reeds to the cage.
The engine won't like digesting one.