How to clean CV motorcycle carburetors step by step

The carburetors used in this "how to" article are from a 1993 Kawasaki zx6e.

Most 1cyl, 2cyl, 3cyl, and 4cyl street legal motorcycles will have carburetors similar to theses.

You will need:

-tools

-can of OMC marine "engine tuner" carb clean (from any Johnson/Evenrude marine dealer)

-can of aerosol brake cleaner

-air compressor with "blower tip"

My main advise with carburetors would be to be VERY thorough the FIRST time or you will be doing it all over again.

Read all step before you start!!

Step 1:

clean excess dirt, oil, and junk from the outside of the carb bodies with brake clean

drain and remove carburetors.

step 2:

remove top covers, vacuum diaphragms, and springs.

carefully check for any rips or warping in the rubber of the vacuum diaphragms.

replace any damaged ones or all 4 as a set. (keep the old good ones as spares).

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step 2:

remove breather tube(s).

fuel line too if you want.

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step 3:

remove float bowls.

tapping on the face of each screw head with a flat punch and a hammer before you try to unscrew them.

this shock loads the threads loose and flattens any 1/2 stripped screws heads.

use a new, good quality screwdriver to remove all screws.

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step 4:

remove floats. and float needles.

inspect float needles for damage. check to see if any are floats are "sunken" (filled with fuel or water). replace as needed.

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step 5:

remove float needle seats.

inspect o-rings and screens. replace as needed.

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step 6:

remove main jets and emulsion tubes.

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step 7:

remove pilot jets.

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step 8:

count the turns in it takes for the pilot mixture screw to seat LIGHTLY in the bottom of the threaded hole.

write down the number of turn in case you can find the specification for your bike.

remove mixture screw and spring.

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step 9:

remove small washer and o-ring from mixture screw hole.

you can make a hook tool from tie wire!

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step 10:

remove intake plate and boots

lots of bikes NO NOT have this plate, if so ignore this plate!

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This is the "carb clean" you want to use. it is by far the best and strongest stuff sold. its cheap, $7-$10 at any OMC outboard dealership.

"motorcycle carb clean" like the Honda stuff work OK but nothing like this stuff (Honda carb clean is 2x the price too).

Warning the active chemicals in this "engine tuner" are VERY BAD FOR YOU!!! ware goggles and gloves!!!

wash immediately if it comes in contact with skin.

call poison control then get to the hospital if it gets in yours eyes!!

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Step 11:

spray "carb clean" into every passageway, hole, and vent you can find on all sides of carbs.

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pull chokes open to get "carb clean in that end of the choke passage.

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step 12:

remove and clean large o-rings.

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step 13:

clean carb bodies.

i use the "carb clean" run off in my tray and an old tooth brush.

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Edited by simon@vic

next you will want to rinse the bodies in a solvent tank. and or an ultrasonic parts cleaner if you have one of either.

if you don't have either then you can use hot water but the run-off is toxic. (needs to be disposed of with used oil??)

step 14:

using safety goggles/glasses/face shield, blast out every passage with compressed air.

note the vapor coming from each similar passage. they should be equal on all carbs 1-4 for each passage.

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step 15:

using safety goggles/glasses/face shield, blast out every passage with "brake and parts cleaner". any brand is fine.

note the flow of brake clean coming from each similar passage way of the different carb bodies.

EG: the spray going into the carb from the pilot screw hole should be equal on all carbs.

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carb bodies are now clean. the remaining brake clean will evaporate or burn with the fuel.

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step 16:

put main jets, emulsion tubes, pilot jets, float needles, float needle seats, and mixture screws in a small container.

fill 1/2 way with "carb clean", put lid on and shake it softly for a 5 min. drain "carb clean" and rinse with brake clean.

hold each jet up to the light and look through the hole. they should be equal.

if they are still plugged you can use one strand of a broken or frayed cable to push out the blockage.

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step 17:

scrape any gunk from the bottom of the float bowls with a small screwdriver.

fill with "carb clean" then rinse with brake clean.

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step 18:

re-attach the intake plate and boots. don't forget the o-rings!

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step 19:

install main jets, emulsion tubes pilot jets and float needle seats.

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step: 20

install mixture screw, spring, washer, and o-ring. turn until it seats LIGHTLY in the bottom of the threaded hole.

turn back out to your bikes "pilot mixture screw" specification. normally about 2 turns out or 1.75 to 2.75 turns out.

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step 21:

install float needles and floats. set float height.

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step 22:

check float bowl gasket o-rings for cracks or being "flat". replace if needed.

install float bowls.

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step 23:

install diaphragm and springs.

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step 24:

install diaphragm top covers. be very careful the top outer rubber lip is in its grove in the top of the carb all the way around.

if it is not properly sealed all the way around on all 4 carbs the bike will not throttle up. if they seem stretched you can put the rubber end in a pan of freezing water. this should shrink them down to there org size for installation.

another trick is to hold the slide 1/2 way up with a finger thorough the venturi, fold the rubber down towards the top of the carb bodies. with your 2 extra hands (you will need help) use 3 small flat blade screwdrivers horizontally to hold the rubber lip in the grove. then with the 4th hand push the cap down onto the screwdrivers. then pull them out one by one. i guess this method could be downgraded to "road side fix" if the freezing water works.

also when all is said and done (together) you can lift each slide through the venturi and let slide back down on the spring pressure. there should be some resistance and an "air sound" should also be equal. if one or 2 close too quickly with a smack as they hit the bottom then you didn't get that one sealed properly.

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step 25

install carbs on bike and synchronize.

i will be doing another ones of these for the FCR carb soon.

Edited by simon@vic

Thanks for taking the time to put this all together! I have a couple of comments based on many years of grazed knuckles...

1) Clean the carbs thoroughly before you take 'em off. Obvious really, but dirt on the outside will get on the inside and you'll save a bunch of time in the end.

2) Being a cautious type I would keep components from each carb separate - especially float needles and seats. Cleaning each carb's bits and pieces separately won't add a lot of time to the job.

3) Refitting diaphragms into their grooves in the carb bodies can be an exercise in patience - get it 95% seated and it can ping out (unless you have four hands!). As simon@vic says it is imperative that they are seated properly. The tiniest smear of grease in the locating groove will hold 'em in place. Don't use too much now!

Finally, I've seen the occasional grey import bike (made for the Japanese home market usually) that is restricted in it's Keihin CV by preventing the slide from opening fully. The restriction is in the carb top casting and the cure is either to buy different tops (expensive if you need four) or a bit of love from a Dremel. It's a rare situation but I thought I'd throw it out there...

Finally, the op's excellent post shows the importance of having a clean, well-lit work area and the correct tools. :excuseme:

lay the diaphragm end of the slide in a pan of freezing water, they'll reinstall with less stretch

freezing water shrinks the rubber? nice tip!!

some time they are so swollen i feel like throwing them all out and ordering new ones ($200-300 in some cases). another trick is to hold the slide 1/2 way up with a finger thorough the venturi, fold the rubber down towards the top of the carb bodies. with your 2 extra hands (you will need help) use 3 small flat blade screwdrivers horizontally to hold the rubber lip in the grove. then with the 4th hand push the cap down onto the screwdrivers. then pull them out one by one. i guess this method could be downgraded to "road side fix" if the freezing water works.

also when all is said and done (together) you can lift each slide through the venturi and let slide back down on the spring pressure. there should be some resistance and an "air sound". they should also be equal. if one or 2 close too quickly with a smack as they hit the bottom then you didn't get that one sealed properly.

1) Clean the carbs thoroughly before you take 'em off. Obvious really, but dirt on the outside will get on the inside and you'll save a bunch of time in the end.

thank you! i missed that one. im going back to add it. i normally use the brake clean to hose it down before i take anything apart.

2) Being a cautious type I would keep components from each carb separate - especially float needles and seats. Cleaning each carb's bits and pieces separately won't add a lot of time to the job.

i used to do this and even did in my piles. when cleaning i just toss them all in the same tub now.

i figure if there is anything wrong with the needles or seats im going to replace them any way.

good tip none the less thx!

3) Refitting diaphragms into their grooves in the carb bodies can be an exercise in patience - get it 95% seated and it can ping out (unless you have four hands!). As simon@vic says it is imperative that they are seated properly. The tiniest smear of grease in the locating groove will hold 'em in place. Don't use too much now!

if doing this, make sure it is a grease that wont degrade rubber. there thin and anything seems to destroy them.

Worth brake component grease would be fine!

i used to do this and even did in my piles. when cleaning i just toss them all in the same tub now.

i figure if there is anything wrong with the needles or seats im going to replace them any way.

S'cool, it's just a habit I've got into. I'm sure I once saw a bike with the centre cylinder(s?) jetted different from the factory than the outer cylinders. Can't recall what it was though! Old bike and old age...

Many multi cyl 4's were jetted different, and /or synced the center carbs off from the outer carbs. Many theorys and school of thought about why, but off topic.

:thumbsup:"use a NEW, good quality screwdriver to remove all screws.":thumbsup:

This is the number one rule with carbs... there's nothing like stripping the last screw...

Excellent thread with great pics! -BIG DAN:thumbsup:

that is called "cross jetting".

if your bike is cross jetted normally the #2 and #3 carb have slightly bigger main jets (same pilots). the theory behind this is that the inner 2 cyls get slightly hotter the the outside 2. there for atomizing the fuel more. so for things to run more evenly they give the inside 2 cyls slightly more fuel. a cross jetted V twin or V 4 will have the rear cyl(s) richer for the same reason.

i will also add this when i do my editing.

thank you for the input!

you will sometimes see 2/3 jetted leaner as well. theory being they run hotter and thus richer.

ive done lots of testing with this and have found more by tuning each individual cylinder rather than making a guess that 2/3 are the same and 1/4 are the same.

reality is they are all different.

ive done lots of testing with this and have found more by tuning each individual cylinder rather than making a guess that 2/3 are the same and 1/4 are the same.

reality is they are all different.

EXACTLY!

every carb body is slightly different in ways you can see and ways you can not. individuality tuning carbs is defiantly the the way to go to get max HP if...... you have a dyno and an EGA and a shit load of time. but it is basically a thing of the past now that most people have EFI bikes.

i find with a 4cyl carb-ed bike as long as you. clean carbs properly and get all the right jet in the right place (if they be stock or a jet kit) it will run better then most people need.

you will sometimes see 2/3 jetted leaner as well. theory being they run hotter and thus richer.

i have seen that too but its rare and i couldn't think of one bike off that that is jetted that way. that is one of the things you check 3 times in the carb specs when you pull apart a customer bike for a carb clean and it seems "back words"

more great input, keep it coming!

do you still have the old burned drz s?

you can actually tune each cyclinder individually with the powercommander and bazzaz controllers for FI bike.

zx7's were jetted leaner 2/3 than 1/4.

i parted the burned drz out a few years back.ive owned several in the period of time ive been here.

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