How to Clean your Carbs. as well as install Jets and Shims

by Greg Cothern (MOOT #1) on 9/19/2006

OK several have asked if I can do a write up on how to clean the carbs on a Magna. This will be an exact reference to the non California model ’94-’03 Magna’s but a lot will hold true to the previous generations as well but they will be different. Cali models have many many more hoses, LoL, but basically the same.

I have done over 25 of these on the ’94-’03 Magna’s and it cures the midrange issues as well as the deceleration popping.

If you are running aftermarket exhaust and K&N air filter then I would also suggest the Dave Dodge main jets (105s are what he sells and work great!!!) I DO NOT recommend the Dyno Jet kit either, as they have you drill the vacuum slides, they are expensive. Dave’s setup is a simple install and no part
modifications necessary.

First make sure you have a good clean place to work, assemble your tools with a good setup metric socket set, wrenches, screwdrivers, and basics.

A tip when removing bolts and screws: If you are able, put any removed bolts and screws etc. back into their homes. If you can’t, I recommend a multi-compartmented plastic tray for those loose items.  (I generally use all the compartments and keep my loose fasteners separated by their various placements)   This will assist you in putting the correct screw or bolt or whatever back to its proper home once re-assembly is started. An added bonus is that you are less likely to lose anything during teardown and assembly.

Pull the seat by removing the 12mm bolts.

Tip: Once the seat is removed I place a shop towel over the battery box area to keep from inadvertently shorting the battery if I place a tool on it.

Next turn off your fuel (it would be a good idea to have a near empty tank) at the petcock.

With a 6mm Allen wrench; remove the bolt holding the tank, lift up rear of the tank to remove the fuel supply line. Place a shop towel under the petcock to catch the little bit of fuel that will drain from the hose. Take a big flat blade screwdriver to help with “breaking loose” the hose then gently twist and pull. Remove the shop towel that now has fuel on it, take it out of the work area so you wont have to smell it for the rest of the job. Next you must remove a small 3.5mm vent hose located in the middle of the tank bottom, gently twist and pull, it will come off. Now remove the tank and place in a safe area.

Tip: Take some masking tape and place around the end of the small vent tube you just disconnected so that you will remember to reconnect it when re-installing the tank, I see this happen all the time.

Next you will need to remove the air filter housing and snorkel.

Tip: The screws running around the housing lid are soft, make sure you use a good # 2 Phillip’s and get good purchase so you don’t strip the head.

The lid has 9 screws holding it to the the filter housing. It is a tight fit but the lid and housing will slide out to the left side of the bike with patience. Be careful not to force it as the trumpets for the carbs are soft material that can bend and distort easily. You may have to turn the housing counter clockwise a little to get it out. Patience is the key here – it will come out just don’t force it.

The air filter base has 3 Phillip’s head screws holding it in place. They will usually not come all the way out of the housing so don’t worry it is a design feature so you wont accidentally drop them down a carb. The brackets on each side bolt to the base with 10mm bolts. You will also need to remove the plastic chrome faux air cleaner covers, they have a 8mm bolt in the bottom and 2 tension tab/grommets holding them in place.

On the left side of the bike it’s necessary to remove the entire bracket to gain access to the throttle cable mount. There will be a hose you need to remove along with the choke pull handle, simply slide the idle adjustment knob out of its bail. The right side bracket does not need to be removed, just the bolt at the top holding the air cleaner base in place. There is also a vacuum hose on the rear of the housing base that needs to be removed. Again, patience in removing the air filter base over the trumpets.

Now the top of the carbs are exposed, visually check to see if there is any gross amounts of dirt and or varnish. Remove the 2 Phillip’s screws that hold the throttle cable adjustment mount to the carb body. Gently work the cables loose from the throttle plate wheel, mark each cable if necessary as you remove to make sure you get them re-installed correctly.

The auto fuel shut off diaphragm has 2 hoses coming off one with a “T”. Rremove this from the diaphragm. Usually needs gently persuasion with a flat blade screwdriver to release. Next you will need to loosen the rubber boots (several turns you want them loose quite a bit) at the carbs don’t loosen the bottom at the head intakes. Your are ready to pull the carbs off, but they are in the rubber boots pretty snug. I use 2 small pry bars or very large flat blade screwdrivers wrapped with a shop towel to gently, I say gently break them loose. Make sure you do not pry on them as you are working on a prt that can be broken easily. Patience again is the key. You will see or hear them release, work side to side little bit at a time to make sure you do not damage anything. Once the carbs are released from the boots, you will need to take the choke cable out from under the water pipe.

Now you can take the entire carb bank to the bench to work on after you drain the fuel from the bowls. Be careful the bowl screws are soft. Flip the carbs upside down so the bowls are facing up. With an 8mm wrench (5/16’s also works) carefully loosen the carb bowls.  Once loose enough you can use a # 2 Phillip’s screwdriver. Working one bowl as at a time remove the bowl, clean the bowl with some spray carb cleaner and a old toothbrush, wipe dry with a shop towel. You will see the floats, main jet, and the slow jet.

Refer to the manual so you know which is the slow jet. Remove it with a flat blade screwdriver. It is brass and very easily damaged so be very careful and patient with them. Once removed; use compressed air to blow through the orifice, hold to the light to see the light shine through the orifice. If you can see the light then it is fine re-install, if not then you need to clean it out again with carb cleaner until it’s no longer obstructed. Re-install the bowl and go to the next carb, working one carb at a time.

If you plan to install main jets for your aftermarket exhaust then do it now, I recommend the Dave Dodge jet kit. It is the easiest to do and works great, www.drp123.com. Go the contact page and call  or email him. The Jet and Shim kit will have great instructions and a tool as well as the jets and shims. The tool is what you will use to adjust the pilot screw. When adjusting the pilot screw I recommend removing it; being careful not to lose the spring, and cleaning it with carb cleaner, then re-install.

Tighten down to a light seat (remember it is brass and will easily damage). Once at the light seat back out 2 3/4 turns for completely stock setup. 2 7/8 turns for modified stock mufflers, 3 turns for modified stock mufflers and K&N air filter and 3 1/4 turns for aftermarket exhaust and K&N filter.

If installing shims which I highly recommend no matter what, then remove the 3 screws holding the black plastic cover on (be very careful that you do not strip these screws as they are very soft) (This is a great time to replace these soft easily stripped Phillip’s screws with good quality Allen head cap screws 4mm x 16 mm long, you will need 3 per carb for a total of 12. Remember the cover is plastic, do not want to break it by over tightening.) Remove the diaphragm spring and diaphragm/vacuum piston containing the jet needle being very careful not to tear the diaphragm. Remove the jet needle holder from the piston by screwing one of the cover screws in the holder, gently pull the holder. Carefully remove the jet needle and the 1 factory installed shim. Add the Dave Dodge shim in addition to the factory installed shim, I have always just added the additional shim on top of the factory shim. Re-install the jet needle in the vacuum piston and replace the holder, make sure you fully seat the holder into the piston, it has an O-ring and needs to be fully seated.

You are now ready to re-install the jet needle vacuum piston assembly back into the carb, be very care to not force anything as the jet needles are very susceptible to damage and life will be bad. They will only fit one direction and the needle has to insert into the main jet.

Once the piston assembly is back in place carefully fit the diaphragm back into its seat groove, you will need to exercise great patience in replacing the diaphragm making sure it is in the seat correctly. Insert the spring and carefully line up the cover while seating the spring into the piston housing, it will try and bend around but gently persuade it to go straight with a small screwdriver or such. When the cover is fully seated and you are sure the diaphragm is seated and the cover fits flat and smooth replace the 3 cover screws. You are almost done, just have to do this 3 more times, LoL.

Now to re-install the carb bank back onto the rubber boots. You will notice on the top of the rubber boots to the middle of the engine “V” there will be 2 little guide horns, you must make sure these are outside the carb bore. Straddle the bike with 2 shop towels placed on the top of the carb housing, push firmly and evenly to seat the front bore’s into the boots, check to make sure the guide horns for the rear boots are still outside the carb bore then firmly and evenly push down to seat the back bore’s. Once the carb bore’s are fulling seated in the boots tighten the clamps on the boots making sure to get them tight but not damaging the clamps. Re-install the removed vacuum lines and throttle cables, side brackets, air filter housing, etc and go ride (Crank the bike with the throttle closed to activate the fuel shut off diaphram to fill the bowls quicker)!!!