Now we have the carburettor out of the bike we need a nice clean work area. Some nice clean rags and a work space where small bits can’t get lost or roll off the bench. We also come to a dilemma in my normal, cheap-as-chips servicing guides – I use an ultrasonic cleaner to clean my carbs. Not that ultrasonic cleaners are that expensive these days, but I can understand if someone didn’t want to spring for one just to do a single AG200 carby.
After years of doing it with the basics, like carby cleaner and compressed air, I found that with AG bikes, the neglect has usually been severe. The built up crud from around twenty thousand ag-kilometers (equivalent to one hundred thousand normal Kms 🙂 ), and then getting chucked in the shed for 10+ years to let corrosion and old fuel do their work…well, sometimes carby cleaner isn’t enough.
It all depends on the condition of the carb. If the bike is running and is not too old then a bit of compressed air and carb cleaner may do the trick, but so many times I’ve had to remove the carb multiple times to get it right. I will admit though that was always with bikes that were really bad. What I like with ultrasonics is that you get it right every time. Its very effective when the carby is fully disassembled.
So all I can do is roll on here and show you how I do it and I suggest you get yourself a can of carby cleaner and access to compressed air if you want to do it without ultrasonics. Carby cleaner will still work well if you disassemble the carb like I do here and clean it all out and make sure any varnish, dirt and corrosion is removed. It may take a bit longer and you might have to be a bit more observant on your results but in the end you will get the same thing – a nice clean carb that works the way it was supposed to when it left Yamaha.
I will make a quick mention about tools; I have already done a post on JIS screwdrivers, you can get by without them and good quality screwdrivers (especially European ones) seem to fit reasonably well – just be careful and observant. If the driver doesn’t fit nice then try another. Screwdrivers for the slotted heads on the jets are a different story. Don’t tolerate a poor fit here; they are made of brass and there is a good chance they are effected by corrosion, varnish and/or caked on sediment. You will only get one chance with these jets. If you hack the slot on them you will be in a whole world of pain trying to get them out.
OK, the first thing to do is remove the top throttle slide/diaphragm cover. It pays to check this first because if the rubber diaphragm is split or torn then you need a new one and if you don’t want to pay for the Yamaha part then there is no point going on with the clean. So remove the four screws and remove the pressed steel diaphragm cap and slide spring. Slide the throttle slide and diaphragm assembly out and inspect the rubber closely. If it looks OK, store the assembly so it isn’t placing any weight on the diaphragm.
If all is good then you can proceed to disassemble the slide/needle assembly. Look down the top of the slide and you will see two Philips screws holding a metal plate. Have your wits about you when you remove the screws because there is a spring under it. Don’t get too stressed about how it all goes together because I will show all that in the re-assembly blog that’s to come, just make sure its all in bits so you can clean it up good. It also might be a good time to inspect the needle and take note of any wear because it will be helpful in diagnosing any running problems later on when its all back together. Cleaning will only do so much on the AG200, if the needle and emulsion tube are worn, the bike wont run well and you will have to replace them as a set. I will cover this after this series on carb cleaning.
Time to remove miscellaneous bits off the carb body now. Start with the three hoses if they are there – the fuel line, bowl drain and float chamber vent. Remove the idle control adjuster and spring and the throttle cable holder bracket.
Now we turn our attention to the top of the carburettor. The picture to the left shows the pilot air jet (1) and the pilot screw (2). If they look like they have corrosion issues (especially the jet) then a squirt of your fav. penetrate and a cup of coffee might be what you need! Otherwise just unscrew them and put them aside. Just be aware of the spring under the pilot screw when you remove it and down underneath that spring will be a steel washer and under that a tiny o’ring. These parts are tiny and like to flick away onto the floor or in other dark places never to be seen again so be on guard!
Now we have a nice flat surface to stand the carb on the bench upside down so we can concentrate on the float and underside parts of the carby. Remove the float bowl drain screw first then the four Philips screws holding the bowl on. Remove the bowl and you should be greeted with something similar to as shown here on the right.
A bit of a look in the bottom of the float bowl will tell you (if you don’t already know!) what sort of a battle you will be up against with the rest of the carb. Is there corrosion or just varnish or neither? While you are looking, remove the plastic shroud from around the main jet and the rubber plug from the pilot jet tube and the bowl gasket and put them aside.
Get yourself a fine pin punch and lightly tap out the float pivot and remove the float and the needle from the needle valve assembly. I have read so many horror stories about Mikunis and their float pivot post breakages. I have never found one in an AG200 to be that tight that it causes issues, but be careful with it and if tight, relive pressure on the post by laying it on a solid surface. A single Philips screw fastens the bracket that holds the rest of the needle valve assembly into the body of the carb. Sometimes the needle valve needs a bit of persuasion to come out because of the rubbish that can accumulate on the filter on the other end of the valve, a bit of penetrant to soak down onto the o’ring can help things out here.
Take a look down the pilot jet tube and see how bad it is down there. If there is a lot of crud, try to get as much of it out as you can before attempting to remove the pilot jet. Some carby cleaner and compressed air should do the job. When you have it as clean as you can, put a good fitting slotted screwdriver down there and undo the jet. Now do the same to the main jet using a larger slotted driver and also remove the brass washer under the jet. After you have done this I use something plastic like a cheap pen case to tap the emulsion tube out through the top of the carburettor.
Now we could end it here and say the disassembly is complete and cleaning can commence, but I will give the reader the option of removing the throttle butterfly and shaft assembly. I often wonder if Yamaha ever expect it to be removed with the pressed on cap over the end of the shaft, but if the job is to be done properly then it should be removed and cleaned up. Having said this, I have left in place to do cleans where the carb is in pretty good condition. There are no air or fuel passages involved with theses parts so If the bike doesn’t run correctly it will be related to another area of the carburettor. I will leave it up to the reader on what they want to do but I will document the procedure below.
If you look closely at the photo at left you will see where I have the screwdriver placed to lever off the shaft cover. There is a nib in the alloy casting of the carb that will allow you to use as a fulcrum of sorts to lever the cap off. under the cap is an E clip that can be removed along with a fibre or plastic washer. There are rubber seals at each end of the shaft that fit into the carb casting, keep an eye on them. If they don’t want to come out while the shaft is still in place then leave them until you slide it out.
For the shaft to slide out, we now need to remove the two Philips screws holding the butterfly to the shaft. The brass butterfly plate passes through a slot in the shaft and is a pretty tight fit so be patient removing it so you don’t damage (especially the edges) it. Take note of its orientation to make it easier for you to re-assemble. Be careful the return spring doesn’t skewer you when you slide the shaft out and watch for the seal on the spring side of the shaft.