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Carbs/Fuel System - Troubleshooting

WARNING - you may actually be able to fix your own carburetor after reading this section!

Choose your repair method:

Quick fix  Not-so quick Fix   Half a day Fix 
(if you're lucky) (tough luck. could be worse) (what did you do to it?)
 

So how do you trouble-shoot the darn things? Well, hopefully having a better understanding of how they work will help you not fear their disassembly. First and foremost, if you haven't already done so...buy the shop manual. If you canít get your hands on the original factory manual which, unfortunately, is usually worth the small fortune they cost, buy either a Clymer manual or a Haynes manual. Regardless of whether youíre a cheapskate or not, you may have to take the carbs apart.

TIP

When taking carbs apart, always do it one at a time so you can look at the others to see how they go back together!

 

The Quick Fix

I always say that it pays to try the easy, cheap things first. I've had this work for an awful lot of the rough-running bikes with carb problems I've worked on:

Try putting a whole bottle of extra strength GUMOUT in a full tank of fresh gas. If you have to, drain the old gas (if itís been sitting for more than a month) and use it in your lawnmower. After the Gumout and fresh gas is in, run the bike for a while. If you can, ride the bike for an hour or so at varying speeds to effectively work the GUMOUT through the carb system.

The Not-so Quick Fix: 

(do this with a friend)  

BE CAREFUL WHEN WORKING WITH GASOLINE. Make sure you are well ventilated and AWAY from any sources of heat or spark. Disconnect the gas tank (it should be able to be disconnected without draining Ė unless your tank valve is broke). Remove the gas tank from the motorcycle and set it on some cardboard (be careful not to bend the fuel valve). Keep the key out of the ignition. Drain the carb bowls (it's usually a screw on the very bottom of the carb body) into an empty container one at a time.

Tip

Attach a clear plastic hose to the nipple on the bottom of the float bowl (buy about 3 ft of 3/8" tubing from a hardware store). Don't drain the gas into styrofoam, gas will melt right through it (donít ask me how I know that!).

If you can, remove the bowls from the carbs one at a time, without removing the carbs from the bike (be very careful NOT TO BEND THE FLOATS!!!). If you cannot do this without having the hands of an infant, sorry, you must skip to the next section. Be sure to hold the floats up and donít let them hang. While you or your friend is holding the floats, clean out the bowls with a can carb cleaner (buy the cheapest stuff money will buy at the auto parts place) and a lint-free rag (donít leave any shnibbles of fuzz in the bowl) Take the carb cleaner can with the attachment hose that comes with it and spray it up into the jet nozzles. Again, be careful with the floats! The jet nozzles stick out from the bottom of the carb and usually look like little brass slotted cones with holes in them. Hold the throttle part-way open and spray a bit of carb cleaner up the bigger jet nozzle(s) as well.

Use the carb cleaner to clean off any visibly "varnished" pieces of the carbs. As always be careful NOT TO BEND THE FLOATS!!!- did I say that yet?

Reassemble, and go on to the next carb. After you are finished, reassemble everything, put the tank back on and reconnect all fuel and vacuum tubes. Turn the fuel tap to PRI to get some fresh gas into the bowls. Check to be sure no gas is leaking.

Half a Day (but thorough) Fix:

Drain the carbs (unscrew the drain plug at the bottom of each & catch the gas in a glass jar below). Take the carbs off of the bike. This usually involves removing the fuel line, the choke cable and the accelerator cable (and the deceleration cable if it has one). You may also have to remove any vacuum hoses that may be attached either to the carbs, or near to them (label where they go or take a Polaroid or a digital picture before you do it if youíre afraid youíll forget where they go). The clamps at the engine side and the air filter or airbox side will need to be loosened or removed. Sometimes the airbox also needs to be removed or at least loosened to give you the "play" necessary to take the carbs out.  When taking them out, be careful not to bend anything on the carb body.

After I perform the above-mentioned steps, I usually take the carbs out by straddling the bike with the seat off. I then grab the bank of carbs from each side of the bike, and pull back (pretty hard) towards the rear of the bike (which smashes the rubber boots on the inlet side a bit). Once the carbs snap out of the boots on the engine side, rotate them in your hands so the bowls are either facing the front or the back of the bike (or whatever angle will make it work!). Slide them slowly and gently out of the side of the bike.  Stuff some clean rags into the holes on the engine side of the carbs to prevent junk (or rodents!) from getting in the cylinders.

Once the carbs are out, place the assembly on a table with a piece of corrugated cardboard underneath them.  Prepare for carb disassembly by doing the following:

  1. Put a towel over the cardboard to prevent the small pieces from rolling if they fall out of your hands.
  2. Make sure you have a can of carb cleaner.
  3. Get a small empty, clean tin can (a tuna or soup can works great) for cleaning parts in.
  4. Either use an air compressor or buy a can or two of compressed air (found anywhere computer accessories can be found).
  5. Get yourself an old toothbrush for cleaning the small parts.
  6. Make sure you have good lighting.
  7. A small flat-head screwdriver.
  8. A Polaroid or digital camera (optional).

Once you have gathered the above items, flip the carbs over such that they are upside down (the bowls facing up). Donít be surprised if a little bit more gas comes out. However, if a lot of gas starts to come out, flip them right back over and try to drain the gas out of the offending carb by reopening the drain valve over your can (take the screw all the way out if you have to).

Next, starting at one side, remove the 4 screws that hold the bowl onto the carb body. Depending on how frozen the screws are, you may have to have someone else hold the carbs for you as you loosen the screws.

Tip
If your carb screws are absolutely frozen, try putting your screwdriver in the screw and give the screwdriver a couple good whacks with a hammer. Still no luckÖ you usually can grab the screws from the side with a smaller pair of Vice-Grips. Just remember that once you trash the head of the screw, bring it in to your local hardware store and get FOUR replacements (or 4 for each carb that has stuck screws). Donít just replace one screw on the carb, cheapskate!

Once the screws are out, slowly pull the bowl off (if it is stuck, gently tap on it with the handle of your screwdriver). Set the bowl aside and clean it out with carb cleaner and a clean, lint-free rag. Be sure there is no sediment in the bowl. Youíll now be looking at the float(s) and the jets. From here, you can decide what you want to clean off/out first.

Next, take the floats out. If you look where they pivot, youíll see a little bar that holds them in. Once the bowl is off, you should be able to take a piece of wire or a punch and push the rod a bit to the side. Depending on how neglected your carbs are, this may be difficult. Try soaking the rod and pivot point in carb cleaner for a couple of minutes before trying again. You have to be careful not to bend the carbs, they are extremely fragile. Once you get the rod out, the carbs should pull right off. BUT, when they do, theyíll probably take the needle valve with them. This is a teeny little needle that usually has a little spring loaded bump towards the top (away from the needle side). Note the way the needle valve is held to the float assembly and take it off. Once the floats are off, shake them. Listen for any fluid or particles shaking around inside; if you hear anything, the float must be replaced. Carefully clean off the float and needle valve. Set them off to the side.

Tip
If you forget how to put the needle valve back on the float assembly, open up the carb next to the one youíre working on and look at it as an example!

Iím not sure what the professionals do, but Iíve had very good luck removing the jets using a small flat-head screwdriver in an old rag to remove the jets. Most of them will unscrew (counter-clockwise, as usual). I wrap the rag over the screwdriver because the jets are usually made of brass, which is very soft compared to your steel screwdriver. Have someone else hold the carbs steady and unscrew the jets ONE AT A TIME. Each one you take it out, drop it in your can of carb cleaner and clean it out/off as best you can with your toothbrush. If youíre REAL careful sometimes you can use a thin piece of wire (or part of a multi-stranded wire like speaker wire) to fish through the little jet holes to clean any chunky stuff out. Some of the "purist" cycle mechanics might criticize me for this suggestion, but Iíve never (knock on wood) had it damage the jets. Just BE CAREFUL not to scratch or mar ANY PART of ANY of the jets (donít be a bonehead, eh?). After you have taken a jet out, use your can of carb cleaner and spray it up both the jet and where the jet came out of.

If you want to be more thorough, carefully unscrew the plate on the top of the carb (usually 4 screws). BE CAREFUL, because as you take the screws out, the plate will probably start to push off by itself. Thatís because thereís a weak spring (itís supposed to be that way) underneath that pushes the jet needle down. Take the top off, and carefully remove the vacuum diaphragm assembly with the jet needle. Inspect the diaphragm for any tears or dry cracking. If you see either, replace it Ė donít try to repair it. Chances are, you may have to replace the others as well.

While the jet needle is out, soak a corner of the rag in carb cleaner, then CAREFULLY wipe off the needle, taking care not to scratch or bend it. If you do, go buy another one. Leave the jet needle/diaphragm off to the side. Take a look in the carb all around. Hold the butterfly valve (the throttle) open and wipe off any deposits that may have formed. Spray/wipe off anywhere you see a varnished look or black crud (for lack of a better word!). Follow up with a good blasting of compressed air (BE CAREFUL NOT TO BLOW ALL OF THE LITTLE PARTS ACROSS THE GARAGE!) in the various passageways. Depending on the extent of the clogging, you may want to alternate carb cleaner and air a couple times to be sure youíve got it all.

Re-install the jets. Carefully reinsert the diaphragm/jet needle, spearing the needle into the needle jet in the carb body and be sure to insert it properly orientated (they usually have a notch on the diaphragm or at least look at the cylinder in the venturi and make sure itís the same way as the next carb). Donít bend or mar that needle! Put the spring back in (be sure itís centered properly) and reattach the cover. This is sometimes a trick to get everything lined up properly. Tighten the screws, but not really tight. Flip the carb over and reinsert the jets, being careful not to cross-thread them (remember they are relatively soft metal). Tighten the jets down.

This next step is tricky as well. Either hang the needle valve from the float and see if you can reposition the float in its place, or drop the needle valve in place and see if you can get the float to be in place and attach properly to the needle valve. You may have to play with this a bit to get it right. Once the needle valve is properly hanging off the float "tang" (that little metal tongue that pushes on the valve), and it absolutely must be correct for the carb to work right, align the floats and spear the float pin back so itís even on both sides. Check the gasket on the float bowl, replace them all if one is bad (cracked or not continuous). Put the bowl back on tighten the screws.

Thatís it! Take a break and go on to the next one.

After youíre done with all the carbs, take your can of carb cleaner and a tooth brush and clean off all of the linkage and springs on the carbs. Dry it off with your compressed air. A little WD-40 will help keep them from corroding after theyíre clean and dry.

Remount the carbs on the bike and reattach all cables and hoses you disconnected. Hopefully, your carbs are cleaner and work better. Itís usually best to drop a new set of gapped spark plugs in at the same time.

 

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Last Update: Wednesday, December 14, 2005 11:53 PM