How to Clean a Motorcycle Carburetor, the RIGHT way.
Posted on September 1, 2008 | Posted by Evan Fell | 216 Comments
I get asked about Carburetor Cleaning regularly both from readers and from friends offline. So I’ve decided to write a definitive guide for cleaning carbs the RIGHT way. So put your tools down for a minute, grab a beer, and give this a read. You might just save yourself a lot of headache and sweat.
Carbs come in many shapes and sizes. Single carbs, dual carbs, racks of 3, 4 or 6, V racks, carbs with ticklers, carbs with accelerators, carbs with asynchronous designs, and carbs that operate vertically. While working on some carburetors is more difficult (due to design) than others, they all share the same basic components, and the process of cleaning those components is generally indentical.
BEFORE YOU START
Make sure that dirty carbs are actually your problem. Lots of things can make a bike run poorly or not start. Weak battery, corroded electrics, old spark plugs, bad timing, low compression, mis-adjusted valves, dirty air filter, and plugged exhausts can all cause poor running. I’ll write an article on how to diagnose poor running conditions shortly, but for now – lets just deal with the carbs.
OK, SO YOUR CARBS ARE DIRTY
Once it has been determined that the carbs are the problem it’s time to get to it. Some racks of carbs are easier to remove than others. If you’re working on a newer model bike the rubber boots from the airbox to the carbs and the manifold boots from the carbs to the motor should be relatively soft and pliable. On older bikes however this is rarely the case.
First remove the fuel tank, seat, and side covers. Depending on your model of bike other parts may need to be removed too. Â For many single cylinder bikes the carb can often be removed without removing any body work at all.
The bike below is a 1983 Yamaha XJ750 Seca with 4 inline Hitachi carburetors
You’ll want to loosen the circle clamps on all of the rubber boots. Sometimes I’ll even take them all right off (carefully, without bending them too badly) so that they aren’t in the way.
Inspect the airbox. On many bikes it is bolted in place to tabs on the frame. Remove those bolts and try to create as much space as possible for the airbox to pull backwards.
Next, put the bike on it’s centerstand and straddle it facing forward. Put your right hand on the right-most carburetor and your left hand on the left-most carburetor and get ready to sweat. Sometimes you’ll be able to pull the carbs straight backwards nice and easy, but that is pretty rare. I usually end up rotating them up then rotating them down as best I can while pulling backwards furiously. This can really take some work and time, especially if you’ve never done it before. In real extreme cases where you simple can’t get the carbs to pull backwards out of the manifold boots I have a couple tips. These tips should only be used in extremely difficult cases when you have been struggling for an hour and simple can’t get the carbs to pull backwards out of the manifold boots.
Tip 1: Ratchet Straps – This is sort of a last resort, but it has worked without fail for me when I’m pooling sweat on the garage floor and the carbs aren’t budging. Wrap a ratchet strap around one of the outer carbs and put the hooks somewhere on the rear of the frame. Then slowly ratchet the carbs right out of the boots. Be careful not to pull them too cockeye’d or you could damage the boots. Attach a second ratchet strap to the other side if necessary. (Note: you can do this in the opposite direction to force carbs back into the boots once they are clean.)
Tip 2: Full Pull! – You should do this before you do the ratchet strap method above. Sit down on your butt along one side of the bike. Wedge one of your feet up between the forks and the front fender, then put both hands on the same outermost carb and PULL PULL PULL! This might not work so well if you’re short! Ha.
Ok, So The Carbs are pulled back
Chances are the airbox boots are all crammed up now. Do your best to rotate the carbs up and out from the boots and pull them out one side of the bike. Sometimes it’s easier to pull the carbs out one side than the other, so have a look to see if there are frame elements, motor elements, or hoses that may block the carbs from coming out on one side.
Also keep note of the throttle cable(s) and choke cable (if there is one). Now may be a good time to loosen the nuts that hold them in place and disconnect them.
Struggle just a couple more minutes wriggling the carbs out the side.
Ok, You have the carbs off the bike
Make sure you brush off any loose dirt or grime, then flip the carbs over and remove the screws from the corners of the carburetor. Some carbs won’t have bolts in the corner and instead have a wire latch over top which can just be forced over.
Remove the bowls.
If the carbs are real gummed up the insides might look like this:
It’s obvious that these carbs are all clogged up. Some carbs might not look so bad, some might be a lot worse. It’s always a mystery what will be inside the bowls.
Now it’s time to remove the floats. It’s generally a good idea to drench everything in carb cleaner (available at any autoparts store). Sometimes the pins will practically fall right out, sometimes they’ll be so stubborn you won’t think they’ll ever come free. But they will! Carefully push on the pin from either side. Sometimes a nail and a gentle tap from a hammer is helpful. **BE CAREFUL**, using force to remove a stuck float pin can break off the pin tower. If they are really stuck and you can’t seem to work them free here are a couple tips.
Tip 1: Heat – Adding a little flame to the float pin towers can help. **Don’t Burn Down Your Garage!!**
Tip 2: Pliers – Using pliers to gently clamp the end of the pin and push it through has worked well for me in the past. **Don’t break the towers!!**
Once the float pin is out you can remove the floats, the float needle, and unscrew the float jet screen.
Set everything aside. Next remove the main jet, pilot jet, and idle jet (if there is one). They should come out easily with a flathead screw driver.
Set them aside.
Next flip the carburetors back over and remove the caps. Underneath the caps is a rubber diaphram with a spring. Sometimes the caps have a tendency to shoot off the top, so be very methodical when removing the screws. Other times the cap tends to stick down until you start to pry at it, then it shoots off, again, just be cautious and don’t loose any parts.
Next you’ll want to gently pull the slides up out of the carburetor body. You can gently pull on the rubber diaphrams, but be very careful not to tear them. If they don’t come up easily stick your finger into the carb intake and push the slide up with your finger. You can also gently pry it with a screw driver (gently). If it doesn’t want to budge don’t force it. Instead finish reading this article and pay attention to the boiling tips further down.
Now your carbs should be pretty well emptied out. If the throttle on the bike moved fluidly and smooth there is little reason to do much to the carb bodies themselves. However, if the throttle was real sticky or frozen there are a few things you can do to free it up. Sometimes just drenching all the throttle components on the carbs and letting it soak is enough, other times it is not. I generally try not to break racks of carbs apart. It isn’t often necessary and can be confusing to put everything back together in the right places. Also, the little rubber connector hoses and o-rings have a tendency to crack or leak if you mess with them. If you can’t work the throttle back and forth until its smooth have a look at the boiling tips further down.
Keep it Neat
Organization pays off.
Clean the Main, Idle and Pilot Jets
Hold each jet up to the light and see if you can look through it. The idle and/or pilot jets have extremely small holes so make sure you are looking through them straight. If you can see through the jet it isn’t clogged. There could be a little gunk built up around the edges so spray them down with carb cleaner and let them sit a bit.
If you can’t see through the jet it is clogged and needs to be cleaned. Always try the easiest things first. Here’s an ordered list of a few things you can do to clean the jet.
- Blow through it. – Rarely works, but hey, who knows.
- Compressed air. – Force 100 pounds into it. Works occassionally. Make sure to hold the jet tightly so it doesn’t go flying across the garage. You might put the jet back into the carb body to hold it in place for this.
- Soak it in cleaner. – When I first started cleaning carbs I thought carb cleaner would be the magic answer. It isn’t. In fact, I hardly ever use carb cleaner any more, because it simply doesn’t do a very good job of anything but removing varnish from the bowl and slide. But try this.
- Poking it through. – Collect a few different diameters of needle like objects. A wire from a steel bristle brush works well, a bristle from a broom works well, a baby pin, small sewing needle, etc. Very gently try to poke it through the jet. If you are using a metal needle use caution, brass jets can scratch and deform easily.
- Boiling! – This works better than anything. Toss the jets into a pot of boiling water and let them bounce around for a couple minutes. When you pull them out blow some compressed air through them and you’ll most likely be good to go.
Some idle jets can be real tricky and never seem like they’ll be cleaned out . . . Just keep working at it, I’ve never met a jet that couldn’t be cleaned.
Cleaning the Choke and Air Mixture Screw
Air mixture screws have a tendency to strip or break. If the carbs were real gummed up you might find that the air screws are stuck. Don’t force them, if they don’t want to come out, just leave them for now. It is fairly rare that these screws will need to be cleaned because they are above the float level. If you can get them out just wipe them down with carb cleaner and spray some through the jet.
Cleaning the Slide and Needle
These are easy to clean. Squirt them with a bit of carb cleaner, wd-40, or anything similar, then wipe them down with a rag. Once the varnish is gone they’re good to go. Sometimes they get heavy varnish on them which I will scratch off carefully with a piece of plastic. Scratching the slide and needle is a BAD thing, use caution.
Cleaning the Carb Bodies
Use the same squirt and wipe method noted above. Most of the time the other pressed jets and passages in the carburetors won’t be clogged. But if the bike has been sitting a real long time with squirrels in the airbox it is certainly possible. Us a compressor to blow some air into every passage you can see. Listen for the air coming out the other side. If no air compressor is available use a can of WD-40 with a straw attachment.
If some of the pressed jets are clogged it can be difficult to open them up. There are a few things you can do.
- Carb Dip – Most autoparts stores sell carb dip. It comes in a can similar to a paint can and is a VERY harsh cleaning agent. Soak the entire carbs in this dip. This dip can eat at rubber and plastics if they are submerged for too long, so try and remove everything you can from the carb bodies before soaking them. Once you pull them out swish the carbs around in a bucket of water to clean off the excess dip, then hose them down with WD-40 to get rid of the water.
- Boiling in Water – Not many people do this but it is by far the best way of cleaning carburetors. Dropping the carbs into a pot of boiling water will instantly free up stuck slides, throttle plates, and other frozen parts. It will also loosen the dirt and grime clogging up pressed jets and other passages. Just make sure to dry the carbs thoroughly with compressed air or the sun afterwards.
- Boiling in Lemon Juice – There is NOTHING BETTER at cleaning carbs than a giant pot of boiling lemon juice. The acidity from the lemons eats through everything; gas varnish, oil build up, dirt, grime, etc. Sometimes I won’t even bother doing anything but this – I’ll just remove the bowls, remove the caps, then drop everything into the pot and let it sit for 20 minutes (rotate them a few times). The one caveat to doing this is that you’ll want to wash the lemon juice off the carbs as soon as you pull them out. So have a bucket of water ready, or a can of WD-40 to hose them down. Also note that the acidity has a tendency to put a dull finish on the aluminum bodies of the carbs. This isn’t a problem in most cases, but if you must have everything shiny be prepared to do a little scrubbing and polishing afterwards. It may sound weird, but trust me, I just saved you LOTS of time. (Most dollar stores sell 1/2 gallon jugs of lemon juice, so buying a few gallons will only cost you $6. Plus you can put it back into the bottles afterwards and save it for next time.)
Cleaning the Bowls
This is pretty straight forward. Use any of the methods above to tranform your varnished bowls.
Most carb bowls are simple, just clean them up and they are good to go. But I picked this Hitachi’s for photos because they have a jet built into the bowl. You can see the ‘fifth’ hole along the edge of the bowl, that is actually a thin passage that extends to the bottom of the bowl. This is for the idle jet and is extremely important. If these passages are clogged, the bike won’t stay running, period. Use the same poke, soak, and boiling methods outlined elsewhere in this article. Not all bowls have these passages, only some, if your’s don’t – good for you!
Once Everything is Clean
Now that everything is clean it’s time to put it all back together. Take your time and make sure you put everything back where it came from. WD-40 is your friend. When screwing in the jets don’t over do it, they only need to be seated and snug, do NOT use any force putting the carbs back together.
If the bowl gaskets got goobered up you can put a little RVT on them. So long as the float needles are still in good condition leaky gaskets shouldn’t be an issue. However, prudent carb tinkerers may want to order replacements if necessary.
Once the carbs are back together stuff them back into the bike!
Extra Notes
- Rebuild Kits – This guide did not mention rebuild kits until now. Rebuild kits (consisting of new gaskets, jets, needles, etc) can be purchased for nearly any bike, both old and new. 95% of the time these are NOT needed. I have rebuilt enough carbs to block off main street, and only once have I used new parts. ONCE!
- Carburetor Adjustment – Carburetor adjustment, setup, jetting, and synchronizing is a whole encyclopedia waiting to happen. Those topics are not covered in this article, but I will address them in future articles.
- Carburetor Polishing – External carb asthetics will be important to some, and not to others. Cleaning is all I am covering here, this will be addressed in the future.
- Work Space – Make sure you have lots of space to keep organized. I also like to work on a wooden surface because it absorbs the spilled gas and cleaners rather than pooling.
That’s it! You’re Done!
I’ll continue to write a couple more related articles about diagnosing carburetion issues as well as the proper way to adjust, jet, and tune your carbs.
KTM 500mx Piston
Posted on August 30, 2008 | Posted by Evan Fell | No Comments
This is the piston from the 1988 KTM 500mx I picked up (see the previous post).
You can see the giant gouge that was created as coolant flooded into the cylinder from the blown head gasket. When metal changes temperatures that quickly there’s really no predicting how severe the damage is going to be.
The cylinder has a matching scare on it but is otherwise in good condition.
Unfortunately these pistons are a bit hard to come by these days. Some custom piston houses do limited runs from time to time. There are also a few remaining NOS pistons on dealer shelves and the guys over at KTMTalk.com bump into them from time to time while fishing through bins like old vinyl.
1988 KTM Big Bore 500mx Dirtbike
Posted on August 30, 2008 | Posted by Evan Fell | 5 Comments
This is a KTM 500mx bike I picked up as a project off of Craigslist. I have a bit of an obsession with KTM 2-stroke motorcycles.
These bikes were known to be absolute beasts. In terms of power they put the competing big bore bikes of the time to shame. The KX500 and the CR500 just did not produce as much peak power as these KTM’s.
This bike had been torn down when the head gasket blew – a fairly common problem with these bikes due to their insane compression. I got it from the previous owner almost exactly as shown. He had already resprayed the frame and polished up a few bits here and there. Still lots of work to do though.
Riding at Elevation
Posted on August 25, 2008 | Posted by Evan Fell | 1 Comment
I’ve been out riding off-road a lot lately. This week I’ve been riding up over 8,000 feet and wow is it exhausting. The terrain is rough and the oxygen content is low.
If you want to ride up this high and have a carbureted bike you’ll need to rejet. Some bike are more picky about oxygen levels than others, but for my KTM I had to drop 2 sizes on the main jet, 1 size on the pilot jet, and I lowered the needle 1 clip. I’ll put together a good guide for altitude jetting across different motor types shortly.
I’ve Redesigned This Site
Posted on August 25, 2008 | Posted by Evan Fell | No Comments
This site needed a facelift badly. It’s now much nicer. Back to business as usual.
Did I Respond To You?
Posted on June 30, 2008 | Posted by Evan Fell | No Comments
Hi All!
The site has been a bit dormant lately while I’ve been preparing for an all out epic motorcycle adventure. It’s about to begin and this site will be ground zero for all that the trip entails.
This site has been getting lots of traffic lately which is flattering to say the least. As a result I now receive emails on a daily basis from visitors who have questions about their bikes or motorcycling in general. I am happy to answer these questions and they are part of the reason I put this site together in the first place. It brings me great satisfaction to know that I can share knowledge and help others enjoy the hobby I have grown to love so much. I am doing my best to respond to as many emails as I can, but am sad that some have slipped through the cracks. I plan to take a more structured approach to your queries in the coming months and I might even start responding to them here on the website.
Hopefully you can all rest soundly in the fact that despite the slow going recently I have in fact been working on many great bikes. All of which I will post about over the next few days!
Until next time, keep the rubber down.
-Evan
Harley’s Legal Issues Over Time
Posted on May 23, 2008 | Posted by Evan Fell | 1 Comment
I love how passionate Harley riders get about their bikes, but most of it doesn’t make much sense to me. Harleys have been proven over time to be extremely expensive, labor intensive, and prone to breaking down. I’m all for having an old Iron Head motor bike for bar hopping, but if I had to cruise across the country I’d much rather take a $200 Japanese bike from 30 years ago.
I just stumbled upon some Harley arguments on a forum and thought this one was particularly interesting. Please excuse the authors poor grammer!
——————————————————————————–
when harley sued the jap companies for sound ,they tried to copy write the exhust note! what a bunch of pussys!
then they sued for looks… and it was proven that harly stole the looks from indian and excellsor and 3 others!
and as for v twin “harley” motor…it was stolen and copied from Jason A Preswick.
harley sued everybody under the sun! the sued a shop called the hog farm! claiming hog was a harley copy write and that shop was not a dealer.once the jugde found out the shop has had that name longer than harley was in business he told them to go fuck thems.
if harley had more enginers than lawyers,they would have a better bike!
buy the way a honda golw wing is made 95% in the US vs. 60% of a harley!
so much for an american bike! the forks.japan,wires, grips ,lights,shocks,tins,black box, tiawan…….and more.
just so you know,i am a certfied cycle tech from MMI and i works in a few harley shops and have built 3 bikes(helped on 7 others) that got into easyriders mag.
yes i love harleys ,i just hate all of that mine is better than yours bull shit.it makes me sick.there is a reason you can buy a 1970 honda cb 750,that has been sitting for 10 years…clean the carb,new oil ,plugs..and ride away!
its called better enginering.
the only bike in the world that needs more attention and work..and tune ups… is ducati..but atleest they go fast!
-VTF
A Full Garage
Posted on May 21, 2008 | Posted by Evan Fell | No Comments
is a thing of beauty.
KTM 300 EXC on the Trail
Posted on May 21, 2008 | Posted by Evan Fell | No Comments
I’ve been able to enjoy riding the KTM over the last month. It’s an excellent trail bike just like my 1999 KTM 300exc was. The Marzocchi 45mm conventional front end is proving to be a good choice and has nice performance offroad.
I love to wrench on bikes, but its also nice to get out into the mountains and just ride!
1983 Honda XL600R with XR600R Motor
Posted on April 18, 2008 | Posted by Evan Fell | 2 Comments
I’ll be damned if the bike doesn’t look good to boot!
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I have owned nearly every make and model of vintage Japanese motorcycle as well as a number of other Europeans and more modern bikes. I do everything from simple fixes to full restorations. I also travel and ride every chance I get.
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