Carb Cleaning
Cleaning details by Peter Kurzenhauser
editing, additions, and procedures by Jeff Mountin, as well a little tips garnered from the XJ Owners mailing list.
INTRODUCTION:
Peter originally sent this message to the XJ Owners list on 7/31/2000 to which I added a few points. This will need to evolve a bit to accommodate differences between Mikuni and Hitachi carbs, as well as the differences between various models. Additional information is always welcome and will be added.
Peter owns an '82 Seca 650 with carbs. My ride is an '86 MaximX 700 with Mikuni carbs. Removal and installation procedures are based on this model and may vary somewhat. The actually cleaning is mainly Peter's with a few details added by myself.
PRELUDE:
Problems usually occur when the bike has been sitting for months (or years) without use, and without the gas being drained. When this happens, the gasoline in the tank slowly trickles down into the carbs and dries out and forms gum and varnish in the passages of the carb. Other additives in the fuel create even heavier deposits in the bowls and parts that are submersed in the fuel.
Proper storage does much to help reduce the build-up. When the time comes to "call it a season" or are not riding very often, say only on weekends, some things should be done as preventative maintenance:
First off, keep the gas tank full. This prevents rust from building up inside the tank.
Use a carb cleaner or stabilizer in the gas. Seafoam is the preferred cleaner and like Stabil, can be used for storage. This should be added before filling up to both to mix it well with the gas and to ensure that the treated gas is in the carbs as well. Running the engine for a few minutes will work just as well.
With a good cleaner or stabilizer, draining the carb bowls should be considered optional, but recommended, along with then disconnecting and plugging (in case the petcock leaks) the fuel line.
OK, so you have done all this religiously since the first day. Yet still there may come a time when it just doesn't start or run the same.
Build-up from the additives in fuel, not varnish or gum (which are cured by adding a carb cleaner monthly or just plain riding every day), will still mean at some point the carbs will need to be torn down and cleaned.
Regularly, rather than monthly, use of Seafoam (or other additive) in the fuel may help reduce the build-up caused by the fuel additives, but even so the day will come and this tutorial will help make it less daunting that many seem to think pulling and cleaning the carbs is.
This tutorial is not designed to replacing having a shop manual, so you better have one before proceeding. It is further expected that you are familiar with the manual and know the names used for the internal carb parts.
At least until I have enough pics and can get scans of the manual.
PREPARATION:
While the process is time consuming and complex, it does not take a skilled mechanic to do a good job. It only requires basic tools, time, patience, and attention to detail. Expect to spend a day or two the first time, which does not include soaking parts. That can take up to two days.
Some materials you will need:
Carb cleaner - Gumout or Gunk work fine. Will also suggest Gunk's Super Spray, which is by far stronger and should work better for cleaning the interior passages.
Carb dip - Usually comes in a one gallon bucket and has a cage for parts.
Compressed air - Preferably an air compressor. Some have been able to use "canned" air. Canned air can provide adequate pressure, but not the volume, so expect to use several cans.
Dixie cups or other method should be used to keep parts separate for each carb, as well as the other parts removed during this process.
Other optional materials and tools will be noted along the way.
REMOVAL:
Now that you are ready to tackle the job it is time to get started...
Remove the trim pieces on the barrels. They are held on by hex screws with very large heads. Remove the plastichrome trim pieces from the carbs. While not entirely necessary, removing the plastichrome trim pieces from the airbox is a good idea to avoid damaging them come installation time.
Disconnect the throttle, choke, and clutch cables. Move them out of the way.
Tip: Use an 18 mm wrench on the clutch arm to relieve the tension on the cable.
Loosen the clamps on the carb and airbox boots and slide them away from the carbs. The shop manual suggests pushing the airbox boot into the airbox. This is not necessary and pushing them back out is difficult. The clamps on the airbox side should be pushed back right to the airbox or removed.
Loosen or remove the bolts holding the airbox in place.
Pull the relay unit above the carbs from the frame tab and move it out of the way. It will interfere with carbs when removing them.
Will now suggest wrapping the frame with masking tape to prevent scratching and chipping when pulling the carb rack.
Note: Leave the fuel line attached to the T between carbs#2 & #3. It is very easy to break the T and that will require more work.
Now comes the fun part.
First off use the center stand and prepare to use some muscle. Don't be afraid to push hard on the rack. The rack and boots can take the abuse. Make sure that nothing with catch as you push the rack out, so use a twist-tie to pull the throttle linkage up, in, and avoid bending it like I did. Doing this in little steps is easier, less frustrating, and takes less force.
Now pull the airbox back as far as possible. Should it move forward, just tighten up the bolts or have another person assist.
Unless you care to muscle them out, a heat gun or hair dryer can be used to heat up the carb boots. With a heat gun you can heat them to the point where they are uncomfortable to touch making them real pliant. The airbox boots are thin and don't need such treatment.
The first move should be to pull the rack back and up until the top rear of the carbs contacts the frame. This should pop the carbs off the airbox boots about half the way and the bottom of the carb side.
Optionally you could remove the tops of the carbs along with the slide assembly and spring for extra clearance.
Now pull up on the front of the carbs, wiggling a little from side to side, but mainly the right, in preparation for pushing them out in that direction.
(Personally I prefer pulling them off from the right and installing them from the left. For me it has nothing to do with being right-handed.)
The idea is to pop the front of the carbs out of the boot, so they can be pushed off easily, which is to say you could just as well skip this step and push them to the side, but why make it more difficult.
Once that is done apply pressure to the side of the rack and firmly push the carb rack over. Initially it will take more force with all four boots resisting. As you progress over make sure to relieve any flexing on the carb boots to avoid tearing and make it easier as the carb move from boot to boot. Suggest having a flat screwdriver with rounded edges handy, as they will catch.
When only two carb boots remain, it would be a good idea to move to the other side and pull them off the rest of the way.
Congratulations! You now have them off and can move on to cleaning.
After four times, I can have the carbs off in 20 minutes or less.
CARB DISASSEMBLY:
There are two ways of cleaning the carbs. Either leave the carb rack intact or pull the individual carbs out of the rack. Both have advantages and draw backs.
Pulling the rack apart is not something that should be done lightly, as the procedure is more complex. Have yet to do this myself, so won't say much about it other than it allows you to dip the entire carb body for cleaning. Might make the cleaning process easier, but that gain isn't worth the hassle in my opinion. Those that wish to do this can read a manual.
By far more common is to leave the rack holding the carbs together intact.
Before tearing the carbs down there are several things that should be done.
Make sure the brass plugs been removed to allow access to the pilot mixture screws located top, front center. If not, remove them now. Easily done with a sheet metal screw and pliers.
Clean the exterior of the carbs. This is where Gunk's Super Spray works very well. However, use this stuff only in a well ventilated area and take care with blow back. Eye protection might be in order. While this stuff remove just about any amount of crud, a tooth brush will make cleaning the return springs go quicker.
The fuel line should be still attached. You can either leave it on or, with care, remove it. Find that sticking a blunt mini-screwdriver between the hose and fitting makes it very easy to remove. Even so, mine cracked.
After cleaning the outside set the carbs on a bench or table and have your part containers handy.
Reminder: Have the bowls been drained of fuel? If you forgot, you may have been lucky so far, but it will get messy in a moment if you didn't.
Remove the screws holding the tops of the carbs on. Note the locations for the carb bracket and clutch cable guide.
Tip: Rather than using a cup, laying out the top covers as they are might be easier.
Remove the springs and slides. Take care not to damage the diaphragms
Important: DO NOT lay the slides on their side. That will distort the the diaphragm and affect slide operation. Use a cup or jar to avoid this problem.
Remove the choke slide and set off on the side.
Problem: Even with the slide off, the #2 and #4 starter plungers cannot be fully removed. If the passages on #1 and #3 are extremely dirty you may wish to consider pulling the rack apart.
Hitachi: Not sure at this time.
Turn the carbs over, remove the screws holding the bowls on, then tap on the bowls to break their seal with the gasket. With luck the gaskets will remain intact and be reusable. Generally they stick to the bowl and the body.
Remove the pins holding the floats with a roll pin punch. One slightly larger than the pin can be used to start them and a smaller one to push them through. Use light taps to avoid damaging the pin or breaking off the boss on the carb body. Slide the valve needed off the float.
Remove the screw, yoke clamp, and valve seat.
Remove all jets, which include the both air jets, pilot jet, and main jet. The main jet involves three parts. Loosen, don't remove, the slotted main jet. Push or gently tap on the main jet to push the emulsion tube (needle jet) down for removal. There is also a washer under the main jet.
Remove the pilot mixture screws.
Important: The shop manual does not detail them, so be aware that there is a spring, metal washer, and o-ring to be removed. The o-ring was missed my first time around and spent a couple hours looking for two of them after seeing them fly out with the first shot of compressed air to the starter circuit passages.
Drafting notation:
Should be fairly complete to this point.
The rest will be pulled from Peter's original message and my reply.
stuffing that tube up into the passages as far as I can and spraying liberally works better than compressed air. Also get a can of carb cleaner for soaking the carbs in. It needs to be at least big enough to submerge the lower halves of the carb rack into, in an appropriate container, or get two at a time into, or some such arrangement. Remove ALL the rubber parts, choke/enrichment valve, slides, needles, fuel jets, air jets, float valve and float, pilot (idle) screws and their dinky o-rings, etc., and clean them separately.
Note that there are o-rings for the fuel passages between the carbs. They should NOT be submerged for any length of time.
The "emulsion tubes" in the center of the carb are critical for good transition from idle to part throttle operation. These press out the top on the Hitachis (I don't know about the Mikunis) after you've taken out the main jet, slide and needle. They may be pretty well stuck and gummed in there. These have holes drilled in the sides of the tube which typically get clogged--make sure they are clear.
The tube cleaning is easy enough. Just let them soak overnight. No need manually clean them.
I've said this before -
Soak the pilot jets. Soak the pilot jets. Soak the pilot jets.
The passage size and shape makes it next to impossible to completely clean them otherwise. One small particle that is missed is very likely to clog them once more and any deposits left are a foothold for future deposits. When the pilots clog up, the engine will be next to impossible to start, idle, and will not sound right. Should you clean the carbs and end up with a "cold" cylinder, most likely something clogged a pilot jet.
For those that have never seen the pilot jets. Consider that after they are so clean as to look new, it is very hard to hold them just right and see the opening. A single grain of sand could stop them up. Get the picture? White-room clean and an in-line fuel filter after all the hard work.
Compressed air to blow out the passages is a must. Not canned air. Good pressure, but no volume.
Let the carbs soak overnight, then spray out all the passages with the Gumout. Put the carbs back in the cleaner to get the other half, let soak overnight, and spray out again. COMPARE the amount of spray flow you get through the passages from one carb to the next. If one flows significantly more or less, you're not done cleaning! Pay particular attention to the very small passages in the bowl itself (Hitachis) and the small brass pipe that sticks down into the bowl (it feeds the choke/enrichment circuits). There are several passages that travel around inside the carb body. Make sure you follow them from start to finish and get them clean!
Rather than waste Gumout (or whatever) I recommend a can of compressed air. Less chance of blow back, which stings on the eyes almost as bad a jet fuel (the additives are killer), but also has a better "feel" from my experience. Being quieter, it's also easier to actually hear differences.
--snip--
Enrichment/choke circuit: This can cause rich running, especially at idle. I had this problem myself on one of my carbs, and I may still be having that problem on another. You have to remove the enrichment valves on the top front (Hitachis) and make sure they are clean. If they are not, the valve won't seal completely and extra fuel will get sucked into the airstream. Basically, it's like you didn't get the choke all the way off on that carb. Those of you who are complaining of black soot-fouled plugs are prime candidates for this problem. After you get the enrichment valve re-assembled, suck on it or spray Gumout from the supply passages to make sure none of it comes through the valve.
There is a problem with pulling out the plungers on the Mikuni carbs that are racked. Only 2 of the 4 (#1 & #3) have enough clearance. Use a flare wrench or socket to loosen the nets. They are brass and deform real easy. A touch of grease or anti-seize should be used on assembly for the nut and a small squirt of silicone spray on the boot.
Pilot Screws: You must get these out, first by removing the brass or aluminium caps that cover them (on the top front). First turn the screws down to bottom, counting the number of turns. When you put the screws back in, put them all the way to the bottom, then back them out the same number of turns. Don't forget the tiny o-rings, washers and springs, in the same sequence, or it WILL run poorly at idle. Be careful when screwing to the bottom. You want the screw to touch bottom, but don't ram it in there, or you will damage the screws/seats, again causing poor running at idle. Use your judgement. These screws have a long tapered needle that is easily damaged--don't drop them on the floor! Somewhere between 2-1/2 to 3 turns is the usual factory setting
Mine where way off. Have the turns, but know that the outer 2 were bottomed out and one was like 3/4 and the last 1 7/8 or so. I'm the OE and had to drill the plugs, so one has to wonder.
The o-rings were a hassle for me. Didn't now about them or the washer, since the shop manual doesn't break that part of the carb. So when first spraying the passages saw a few things fly out and it took me the better part of an hour to find them. Great fun, especially when I didn't first realize that the 2 *were* stuck with the needle and spring.
Float height: This is critical to correct operation of the carbs at idle and full throttle. Various listers have described using the gas tank hooked up to the carbs off the bike so that they can easily check and adjust the float levels. That's fine and a good idea, but you must also measure the float level with the tube attached to the drain valve with the carbs on the bike and the engine running, to be sure. Set it to shop manual specs. Don't try to make it richer by raising the float level. If anything, you want to err on the side of lower float level than too high.
After setting the float height, use the body of the carb and not the lip that surrounds the gasket surface, make sure that when closed the float does not hit the passage (main air jet on the Mikuni). When set at 17mm, mine might have were the float to be slightly uneven. Use a flashlight to check this or modeling clay. It is possible to notch the exterior of the passage, but do so carefully and make sure of exactly where you want a slight notch.
Reassembly: Follow the shop manual. Also, check the opening and closing of the throttle plates and synchronize them by checking visually and with a strip of paper to make sure they close together. The strip of thin paper is a feeler guage to make sure that one plate isn't hanging slightly open when the others are closed. Put it in the throttle bore on each carb and let the plates close on them. The effort to pull the strip outward should be the same on each bore. If you do this, the carbs will be very closely synchronized before you put the cabs back on the bike, and it will run well. Then do the running sync check to double check and fine-tune. This static sync will also help you find any worn throttle shafts. Finally, lubricate the throttle shafts with oil or chain lube. I like chain lube because I think it stays in there longer. Work them open and shut a many times to work the lubricant into and around the shafts.
Also make sure that the slides move roughly the same for each carb and exert roughly the same force. One time found one that was much slower to return. It is helpful to have a something thin and flat to make sure the diaphragms are seated evenly. During disassembly DO NOT set the slides down, so that the diaphragms are deformed. Makes assembly a real pain. Sometimes it does help to push the slide up a little, but by just barely threading each screw and ensuring the diaphragm fills the indentation all the way around make all the difference to how the slide (and entire carb) operates. A light crease will change how the diaphragm flexes and how smooth and quickly the slide responds.
Now all that is needed are some pics for a how-to page. 8-)
Thinking about getting my carbs anodized/coated to make them look sharp during the off season, so might eventually be able to step-by-step illustrate the procedure.
Jeff "The Mountin Man" - '86 MaximX
(Editor's note: Jeff had not quite completed putting together his illustrated version at the time of his death. If anyone has the opportunity to take pictures for a spread similar to the Hitachi tutorial, it would be appreciated.)