Carb Cleaning by Larry

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Here is a primer on carb cleaning written by Larry. For a more detailed version, purchase the book he has written. I highly recommend it. He can be contacted at: [[1]]

You can buy Larry's book! Larry Cargill's guide to rebuilding the Keihin CX/GL carburetors

Correct Carb Cleaning and Idle Jet

I'm going to start by telling you I just put a new oil & cam chain and mechanical seal in my motor and doing some maintenance after it sat for almost 3 years while I rebuilt my house from an electrical fire. I wanted to update the carbs to the style with the accelerator pump so I could eliminate the stumble on my 78 CX500 Standard during take off. (Later you’ll find out that had nothing to do with it) After 4 bad sets of carbs fished out of the Bay, I finally bought a good enough set to rebuild. I did the normal dismantlement and soaked them it the 5 gallons of Chem Dip carb cleaner, rinsed and sprayed them out with carb spray and 120 PSI air hose. I put the motor in and found the left cylinder was running lean at idle and low end. Even though I didn't even take it out on the road, I could tell. The pipe was starting to turn a deep gold in about an hour or more of tweaking with the motor and the carb synchronizing. The idle mixture screws did not act evenly when I started to adjust them. The right one almost turned in all the way and made the motor run better. It turns out though, that is probably because of the over filling float bowls, or so I though! I'll find out after they are installed and re started once again. I found a way to seal the needle and seat again like new!

One of the main problems with these old carbs, and I suspect many others, it that over the years of use, and lack of service, there are many areas where corrosion an calcium from water in the fuel tend to leave their deposits and clog passages and holes in emulsifying tubes, as well as air bleeds that control the level of fuel that is allowed to be pulled through the fuel jets and passages. Everything in a carburetor is designed to complement and control the next section of the system. If one is out of it designed specs, the next section suffers because of its short-sided ability to do its job adequately. We have all used carburetor sprays and dips to clean them with, and thought we were doing the best that could be done for them! Only to find out when we got it back together that not only didn’t they work right, but also there was something different happening now. Sound familiar? I’m going to show you that there are many small passages that affect the performance of these fuel systems. Many of you will be able to relate to what I show you if you have ever had a set of carbs apart or have an old set sitting in the shed that you thought were junk. Use them to follow this tutorial.

The systems, believe it or not, that control EVERYTHING else in the carburetor, are the idle and air bleed circuits. They affect even the main fuel feed for the high-end circuit.

Because of the need of an online acquaintance, Harold, I decided to explore the idle circuit on a set of carbs with stripped out threads and badly corroded bodies. These would be my sacrificial test beds. I was willing to cut them up if I needed to.

As you may know, there is an idle circuit jet embedded in the body of the carb under a rubber plug. Most that I know of, have never had one of these jets out, or been able to get out to service, or even know what it looks like inside! Under it was a world of surprises to me, as well as it will be to you! As you will see, I found a way to remove the idle mixture jet from the body to inspect and clean the idle system and it's passages. I found that because the idle jet is so high in the carb body, that any water that got into the system over the years, or even moisture in the air, tended to collect on the small holes in the idle jets emulsifying tube and cause calcium to form and block the jets holes. I ripped apart 3 sets of carbs and they all had similar deposits plugging at least a few emulsifying holes and had deposits formed around the space between the jet and the body. That would explain why the idle circuits would not perform properly.

These next few pictures show the removal of the idle jet. I used a screw extractor made by Mac tools that I have had for years. I’m not sure if they still make it, but I’m sure they have them if not better quality than the one I have. I used the smallest size in the set. It was labeled size 1 or 5/64th. I tapped it in with a small hammer to set it into the brass jet. It wont hurt it, or effect the jetting, because the actual jet size is drilled down inside the center of the jet, and there is a free space around the jet and the body so when the extractor is hammered in, it won’t get jammed in while it expands with the pressure.


Now, with a small wrench of some type, I used a small crescent wrench to turn the extractor in reverse, and PULL at the same time.


It might help to heat up the aluminum of the body a little with a low flame torch, but I got all of the ones out this way in good condition. NOTE: Do not use CHEAP extractors, they will break and end up making the project as well as the carb, come to a screeching halt. As you can see, there is a shinny ring around the middle of the jet! This is the step where the jet presses into the carbs body. If you look closely, you will see that a hole above the open one is plugged with calcium.


Because the clogs were from calcium, I went out and got some CLR! Calcium Lime Rust remover to see if it would eat away the deposits left by the water in the idle jets. One of the concerns was would it attack aluminum? Yes, it will, but not as fast as it attacks the calcium deposits. I placed these parts in a full strength solution of CLR, and it cleaned VERY quickly. The deposits were dissolved in about 10 to 15 minutes. While the CLR worked, I noticed that the end of a broken throttle shaft that I put in, the metal end, was bubbling, and the end of the idle adjusting screw that had the aluminum limiter was bubbling a little also. The aluminum throttle plate did not react. After rinsing with water, what you see is the end result. NO CALCIUM DEPOSITS!!!!!

First is the sacrifice of carb bodies and equipment used!


These are the parts I soaked in CLR for about 10 to 15 minutes. All types of metals were represented here! Notice the CALCIUM build up of white on the idle jet!


This shows the start of the chemical cleaning reaction on the metal end and the aluminum in the CLR!


Now you will see there is no more calcium deposit after the CLR soaking, and it did not eat any of the aluminum since I only dipped it for a short time.


After cleaning, I found each orifice size in each hole of the different emulsion tubes and jets. IDLE JET






PRIMARY EMULSION JET (under secondary let)


This is the air cutoff passage port going in under the idle jet. Make sure its clear!


Each air or fuel orifice was checked with a very accurate precision jet drill index to ensure the holes were clean and set to their proper size. I did this by starting with smaller than accurate sizes of each hole, and could feel the gummy or crusty build up inside each one. When I got to the right size jet drill, I could no longer feel the smoothness of the build up in the passage, and I knew I was at the right size for each orifice. None of the holes were drilled larger. I used a small drill jet drill index to size each hole in every jet or emulsion tube! You can see the set in the picture of the idle jet and the drill going into the side holes!

NEW ADDITION; In the original post I forgot to add this! Included it the idle circuit cleaning, there is 3 holes inside by the throttle plate. ALL are directly connected and are ALL a part of the idle circuit. The holes in mine were plugged in various degrees. In order to be able to clean and knock loose the deposits in and under them, I used a welding tip cleaner. It's soft metal and was easy to bend and get in the holes. When you open the throttle plate, you will see 2 more. Clean them out as well, and then spray carb cleaner through them from the same side you entered the tip cleaner. This will spray the dirt and deposits out through the larger holes in the circuit. Blast every thing each way, and all ways possible before you blow it out with the high pressure air blower. This is my worst possible goof up in this post. It is so important to clean these out. These are the idle and off idle system holes that effect the throttle just as you start to add the gas. When these are plugged the transition of the throttle could be a little uneven. Sorry I missed it guys, but it's here now


Now it's time to reset the idle jet back into the body! I use a VERY thin coat of lock tight to ensure it's sealed and tight just at the base where the jet presses into the body! Where the shiny ring is! Don't use so much that it will drain down into the holes and plug them up again. Tap it in securely so it sets tight! Use a brass punch, not metal. It could flatten the end of the jet!


These are the air jets in the top of the body under the piston. I found a couple of these were really gummed up, even after I soaked and cleaned them with carb cleaner and blew them out with 120 PSI air hose. It took the jet drills to clean them out thoroughly. And then sprayed them out with the carb cleaner again and blew them out with the air hose. These are the air bleeds that I mentioned above, that effect the entire fuel circuit and its performance.


I went to a jewelry supply store and got a rubberized fine polishing bullet shaped polisher that had the angled tip to clean the seat for the needle and seat assembly. I put it on my reverse easy out and twisted it about 4 times while pressing in on the seat to clean and polish it. It cleans and polishes the seal very nicely now with no old build up to get in the way to make it leak. The narrow one under it is a brass wire brush that I used to clean out the entire seat assembly. I got that at the jewelry store also.


Just so you can see and understand what is under the seat for the needle and seat assembly, I pulled one out. There is a large area and a tapered step under the seat. It can collect a lot of debris in there, so you need to do all you can to flush it out and loosen all the deposits possible before assembling the carbs. If you thing you have done enough, do it some more! You can't get this area to clean. When the vibrations of a running motor start to loosen up the deposits, they can flow in and under the jets. Clean them some more!


NOTE: DO NOT PULL OUT THE FUEL NEEDLE SEAT. THESE PICTURES ARE FOR VISUAL BENEFIT ONLY. (The easy out will distort the inside interfering with the movement of the float valve.) Notice the step around the seat! This is where the junk collects and settles.


After all this cleaning and re cleaning, these carbs should perform like new. Make sure that after all the drilling and cleaning you spray the carbs out well. There will be a lot of deposits that you are going to be knocking loose and will need to get out of there. If you can, use a high-pressure air hose and a good quality carb spray that does not evaporate quickly, it will eat more out the longer it stays moist.

In the last few years, things have changed in my process of cleaning carburetors. I now use an ultra sonic cleaner with a mix of simple green and water. 4 to 1 mix. Purple Power at the same mix ratio, even works better. Without a doubt there is NO better way to get them cleaned. It cleans out passages inside the carbs that you could never do by hand or with sprays. It is absolutely the best and most thorough way to get your carbs cleaned.

When I was done with the set for my 78 CX500, I no longer had an idle issue, and all the adjustments in the idle circuit worked evenly on each side. Even the discoloration on the exhaust headers stopped changing, and has stayed the bright chrome finish since I have done this procedure.

The responsiveness of the motor has improved drastically, and it seams that my gas mileage has improved as well. I will post those results when I get a better record of what it has done.

If you are not confident that you can perform this procedure, or do not have the equipment to do so, E-mail me if you would like your carburetors done. I would be happy to service them for you!

Good luck, and enjoy the results! Its well worth the time and effort, to rid your self of those gremlins that have been haunting you for so long. Larry

#page-comments Here is a picture by Larry on how the idle mixture screw is to be arranged:

his is a better picture of it. But you can see where it goes in the cutaway.


If your going to do something, do it right, don't do it half [email protected]*d.

78 CX500 Std, 79 CX500 project, 80 CX500C, 83 GL650I

Here is more information from Larry on cleaning the idle circuit:

There is a way you can clean out the low jets center orifice. But remember, you won't know about the emulsion tube side. Hopefully you used an ultrasonic cleaner. You could use a guitar string, but the tip of a cut piece of wire ends up with sharp edges that flare out on each side from cutting it with wire cutters. Those edges will make it VERY difficult to get the wire through the hole. A better choice us to get a micro drill set off ebay. Their very cheap. Now straighten out one of those large paper clips and use JB Kwik to bond the .018" #77 micro drill bit to the end of it. It will cure enough to use in less than an hour to be safe. Now you can ream out the inside of the low jet safely. You should pull out the mixture screws and blow out the debris from cleaning out the jet. This should get the hesitation out if the rest of the system is clean. Set your mixture screws at 2 1/2 turn out to start with.

Just so you know, if there's a lot of build up in the low jets drill passages that lead to the center hole, it COULD end up plugging the center again when it gets loosened up. I use 5 different drill bits to clean each low jet when I pull them out. The larger passages leading to the center need to be clean too.

Good luck and ride safe.


For those of you who have not dozed off and want to read another 41 pages on cleaning the CV carbs, here is a link for cleaning the 4 cylinder CB carbs. Virtually the same carbs as far as cleaning goes, but jet #'s and specs are different. But it may increase you knowledge base.

(Editor Note, the former link was dead so has been deleted from this post)

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