Common Honda GL1000 Carburetor Rebuilding Mistakes

You might consider this item: Randakk’s GL1000 Carb Rebuild Video

Here’s a partial list of problems encountered by amateurs when rebuilding GL1000 carbs. Often, I’m called upon to resolve botched rebuilds by incompetent mechanics, current or previous owners, brothers-in-law, and neighbors. Avoid these mistakes if you tackle a rebuild yourself.


GL1000 Carbs Restored by Randakk Customer Jouko Tomminen of of Lahti, Finland

1. Overestimating your own mechanical aptitude, patience and attention span. This is not rocket science, but it does require a fair amount of planning, calm concentration and methodical execution. Interruptions are death for amateur carb rebuilders. Get all your necessary supplies in advance and block out your entire Saturday.

2. Not doing a valve adjust and compression test. These MUST be addressed before doing ANY carb tuning. There is no point chasing carb gremlins unless you have good compression.

3. Failure to perfect all ignition issues before tackling carb work. There is no point chasing carb gremlins unless you have perfect ignition.

4. Commencing work without access to a good workshop manual. The official Honda manual is best. Others are adequate. Be aware of the infamous “Air Jet Mix-up Problem” with Clymer Manuals. See my Tech Tip covering this for details.

5. Deciding that it’s OK to reuse old rubber parts. This false economy will likely doom you to misery. When the internal o-rings harden they also shrink. This can allow fuel to by-pass the jets and float valve seats. Needless to say, this leads to over-rich and flooding problems. Ditto for float bowl gaskets. Oddly, one of the functions of the fuel bowl gasket is to help form a “channel” from the idle mixture adjustment port to the idle mixture nozzle. When the fuel bowl gasket gets tired, split, torn, overly compressed, etc. this “channel” can get compromised and idle performance deteriorates.

6. Using inferior carb rebuild kits from dubious vendors. You can evaluate and decide for yourself the best kits to use by considering this comprehensive review of available carb kits.  Many GL1000 owners eventually conclude that the Randakk Master Carb Overhaul Kit® for Honda GL1000 is superior and the overall best value:

Randakk's GL1000 Master Carb Kit

7. Insufficient cleanliness. Work area should be well lit and surgically clean. The external surfaces of the carbs should be thoroughly degreased before you crack them open.

8. Failure to use bodacious quantities of compressed air. There is no substitute for 125# psi! These carbs are blessed with a myriad of internal air and fuel passageways that must be blown clean.

9. Failure to pre-soak internal components to facilitate disassembly. I use PB Blaster.

10. Breaking float pivot pin bosses when removing float pins. I use a small pick awl and tap with a toy brass hammer (really!) after pre-soaking per #9 above. If you look carefully, you will notice that one end of the pin should have a slightly beveled tip. This is the end you should tap on. Place the entire assembly on a shop rag or towel on the bench so that the entire rack will “float” across the workbench when you gently tap the pin. If it doesn’t immediately begin to move, try tapping from the other side. If it still fails to move, try more solvent and a longer wait before re-trying. If it doesn’t budge on try #2, try a gentle application of heat from a pinpoint “torch.” If this fails, sacrifice the float and pin and remove with a miniature hacksaw or Dremel. This hurts, but it’s not nearly as painful as replacing the entire carb body! Sourcing replacement carb bodies is very difficult. That’s why we developed this fix for broken float pivot posts.

11. Incomplete disassembly. You’re wasting your time if you don’t address all of these:

a. You MUST separate the carbs from the central plenum to replace:
■ Carb-to-plenum special fuel seals
■ Carb-to plenum “air” O-ring
■ Special gasket that seals the 2 halves of the plenum together

NOTE: I strongly recommend that you leave the decorative chrome trim carb “stay” in place as you separate the carbs from the plenum. This way, the #1/#3 carb pair and the #2/#4 carb pair will stay connected to each other when you remove them from the plenum. You can leave them attached to each other this way throughout the entire overhaul process. For amateurs, it’s probably best not to disconnect the carb pairs. This avoids the rather tedious task of re-uniting the carb pairs correctly. If you do separate the pairs, the synchro links must be joined with a washer on either side of the arm, there is a special connector link that joins the choke butterfly shafts and there is a spring that goes between the 2 throttle butterfly shafts (near the synchro screw).

b. Fuel inlet screen. These are located under each float valve seat. Usually can be removed with a small pick, cleaned and reused If they need replacement, they are only available from Honda as part of the float valve needle and seat assembly.

c. Main Nozzles / Secondary Nozzles. These perforated brass emulsion tubes are located beneath the primary and secondary main fuel jets. They are necessary to premix the fuel into a “froth” to promote proper air/fuel mixing. To remove, they are pushed out from the main carb venturi bore side. Take care because they are easily damaged. I use a #2 sharpened pencil which is the perfect tool for this task (thanks to Mike Nixon for this tip!). These tubes contain many small orifices that are typically clogged in carbs that have sat for long periods with fuel in the bowls. If these orifices are blocked, the air circuits can’t provide sufficient air and chronic richness is the result.

d. Idle Jet…a small rubber “bung” passage plug between the 2 main fuel jets provides access to the idle fuel jet. This jet has an impossibly small orifice and must be removed for cleaning and inspection. This orifice and all the associated passages must be clear for each carb or your idle will be corrupted.

e. Circular aluminum “puck.” This is about the size of a large aspirin tablet and is located beneath the bowl gasket in the main carb body. It’s necessary to cover the access point used in the manufacturing process to create by-pass transfer ports for the idle circuit. It’s mandatory that you remove these to clean the hidden passages. Usually, compressed air applied through the idle mixture adjustment screw hole will pop them out (and cause them to fly across the room!). Sometimes, they are really stuck and solvents are necessary (apply through the idle mixture adjustment screw hole). Occasionally, heat is necessary to free them. Sometimes they won’t budge and it’s necessary to remove them with brute force. In these cases, I “install” a sheet metal screw into the puck to provide the purchase necessary to remove. Unfortunately, the pucks aren’t available from Honda, so if you need replacements, you will need access to a stash of salvage parts or buy Randakk’s exclusive puck reproductions: Click here

f. Carb Top assembly. CV slide, spring and cap must be disassembled, inspected, cleaned, polished and re-cleaned. Same goes for the slide bore in the carb. See Tech Tip Section (“Special Tuning Tips for ’77 GL1000s + Carb Top Service”) for more details on this.

g. Primary and Secondary Air Jets. These are located under the kidney-shaped plate on the top of the carbs (under the cap). These sometimes develop a fungus-like coating on lightly used bikes that will cause all sorts of over-rich problems.

h. Idle mixture adjustment screw

i. Pilot Fuel Nozzle. These small brass tubes enter the main venturi near the throttle butterflies. These are approximately 1/2″ long and have a VERY small orifice. It’s not necessary to remove them (they are lightly pressed in), but you MUST verify that they are clear. If they are blocked, that cylinder will be “dead” at idle.

12. Improper cleaning methods. I strongly recommend against ANY immersion-type cleaning except this. If you “dunk” your carbs in a carb cleaner bath, you risk damaging a large number of felts which lubricate and seal the throttle and choke butterfly shafts. These felts are difficult to replace and there is no source for replacements. Use ordinary aerosol cleaning products instead. I mainly use brake cleaner for this purpose. I use carb cleaner sparingly because it is a more hazardous material and will ruin whatever factory finish you have remaining on the outside of your carbs.

13. Using aftermarket float valve needle and seat assemblies. These are notorious for leaking. Inspect carefully and reuse the original parts. Make sure the seats have Keihin logo marks and “1.0” flow rating mark…otherwise, they are aftermarket. The only way to go is OEM Honda. These are pricey, but easily last 25 years and 100,000+ miles. If there is any doubt regarding their condition, order new OEM float valve needle and seat assemblies from Honda!

14 Air Jet Mix-up problem. The primary and secondary air jets are located under the kidney-shaped plate on the top of the carbs (under the cap). These can be reversed with bad results. Worse, the Clymer manual has misinformation about their correct orientation. See the Air Jet Mix-up ProblemTech Tip for more details on this.

15. Installing main fuel jets upside down. The primary main and secondary main fuel jets can be installed upside down. Not a catastrophic problem. The correct orientation is with the actual orifice oriented “up” (installed position).

16. Failure to align floats. Prior to setting the float height, you should check each float carefully to make sure that it is square, plumb and that the pivot is true. I use a precision right angle device and lots of visual inspection. Adjust each float as necessary. This is a critical step. Unless the geometry of each float is identical, you won’t get consistent mixtures across all 4 cylinders. Poorly aligned floats can “foul” on adjacent structures and cause chronic fuel starvation or flooding. I take an additional step …I weigh all four floats to make sure they are evenly matched. On my scale, clean floats weigh 12 grams. I throw out any outliers than vary by more than 1 gram. The plastic floats used on GL1000s aren’t prone to saturation like old-fashioned floats, but weight-matching is a good idea nonetheless.

17. Failure to clean / ream float pivot holes (on float) and verify that there is no binding on float pivot pins.

18. Failure to check and set float height properly. Believe it or not, floats can be installed upside down by inattentive “mechanics” with disastrous consequences! The correct spec is 21 mm. This is measured from the bottom edge of the float to the raised lip adjacent to the carb body fuel bowl gasket surface. Be sure the spring loaded “tip” of the float valve is contacted but not depressed when you take your measurement. The best way to accomplish this is to set the rack up (on end) on your bench and tilt it slightly away from vertical so that it rests against something sturdy (I use my bench vise). Then measure the floats on the lower pair of carbs. Adjust the “tang” as necessary to get the measurement to exactly 21 mm. Also, when the measurement is correctly set, the bottom edge of the float should be exactly parallel to the carb body along the entire length of the float…not just at one point of measurement. When satisfied with the first pair, flip the carbs over and repeat for the other two. More details on float setting here.

19. Failure to check for air and fuel leaks within the plenum passages. I use a vacuum pump to test these circuits for leaks.

20. Failure to check for air leaks within intake manifolds …mainly at the rubber connectors. Again, easy to check with a vacuum pump.

21. Failure to use all new fuel and vacuum hoses.

22. Failure to rebuild the air cutoff valve. Closely related: Failure to rebuild the air cutoff valve correctly. The diaphragm can be installed upside down! More details here.

23. Failure to service the choke linkage. The choke butterflies operate via spring pressure, not direct mechanical linkage. Any binding in the linkage will result in problems like inability to get full choke on 1 or more carbs or failure of choke butterflies to release correctly. This is a frequent cause of hard starting and over-rich problems.

24. Failure to check / set fast idle free play (between transfer link on plenum and fast idle ramp on carb #4)

25. Failure to implement the “Off Idle Fix.” Probably the single best “improvement” you can make on an early GL1000 (’75-’77)

26. Failure to service the fuel tank, replace external filter, and fuel hoses. Easiest way to contaminate your freshly cleaned carbs.

27. Failure to flush debris from the fuel pump. Another easy way to contaminate your freshly cleaned carbs.

28. Failure to “bench synchronize” the throttle plates. This is a simple visual check to make sure the throttle plates close simultaneously. By checking this before the carbs are installed, you save lots of aggravation later in case there has been an assembly error … especially with the carb throttle plate mating linkage (see #29 below). Hint: there should be a washer on either side of the synchro link which joins the throttle butterfly shafts of each carb pair on the left (2/4) and right (1/3) sides. Ditto for the left carb pair to right carb pair balancer. Obviously, this must happen before the intakes are on.

29. Failure to synchronize carbs once they have been re-installed.

30. Ruining the new-orings for the primary and secondary mains or float valve recesses by careless prep and assembly:
• Jet tower internal bores not cleaned adequately (residue from old o-rings not removed). Ditto for float valve recesses.
• Oxidation inside jet tower internal bores not removed. Ditto for float valve recesses.
• Burrs or other defects inside jet towers from prior overhaul activities not removed. Ditto for float valve recesses.
• Finally, be aware that aftermarket main jets sometimes are not sized properly…the O-ring grooves can be too shallow. This results in the O-ring fit being too “snug.”
Solution: “dress” the jet tower cavities and float valve recesses with crocus cloth or similar to remove oxidation and burrs, CLEAN THOROUGHLY, then use a lubricant like Vaseline to insert the main jets carefully.

The o-rings in Randakk’s Cycle Shakk Master Kits are sized exactly to OEM specs.

31. Assuming the guy who worked on it before you, knew what he was doing. Here’s a report from Randakk’s customer Mike Sayler which highlights this danger:

“The overhaul went very smooth, the pucks came out without any grief as well as the float pins. One of the sync assays (screw set B?) fell apart the minute I separated #2 and #4 carbs. Not a big deal, the arm goes between the two washers, makes sense to me. I didn’t do any mods, just cleaned and reassembled. I replaced the fuel hoses and clamps, flushed the fuel pump and it started right up (After I remembered to open the petcock) Ha!

When I hooked up the merc sticks I noticed #2 cyl was only developing 5 inches of vacuum. All the rest were about 14”. I pulled the plug wire and the engine almost died, so I knew I had compression, spark, and fuel. When I bottomed the mixture screw with no effect, I was sure I “bunged” the rebuild somehow. After an hour of throwing wrenches and inventing new swear words, I pulled the intake runners on 2 and 4 and compared the throttle plate position between the two carbs…WAY OFF! Number two was nowhere near closing. I’m guessing someone has had these apart before, reassembled the sync linkage incorrectly, and adjusted around it since the bike ran relatively well before the rebuild. Putting it back together correctly caused me a lot of grief. (A simple visual inspection could have saved me a lot of aggravation)

I’ve read all your tips on your website, including the most common mistakes made during carb OH. Given the age of these bikes and the certainty that they’ve been touched by more than twelve pairs of hands in their lifetime, I am now certain that the biggest mistake one can make is “assuming the guy who worked on it before you knew what he was doing.” Thanks for all you do.”

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40 thoughts on “Common Honda GL1000 Carburetor Rebuilding Mistakes

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  1. So, probably 3 years ago I overhauled the carbs on my ’78 GL1000 using Randakks carb kit & video. Not new to rebuilding carbs, but used the video, just in case I could learn a trick or two, and I did. Ran great until recently, where I was noticing a loss of power, kind of seemed like I was missing half a cylinder, but couldn’t diagnose it. Tore the carbs off and upon opening the bowls I found the o-rings on all the primary and secondary jets were disintegrating, or melting. I haven’t dug into it further, but disappointed to find this issue. Went with Randakks kit because I’ve grown to hate tearing into carbs repeatedly. Do it once, and be done. Unsure why these o-rings died on me. I’ve run Stabil off and on in our California gas, but beyond that, nothing out of the ordinary. Have there been problems with these o-rings elsewhere? Thanks.

  2. Just want to start out by saying thanks for all the info on doing GL carbs, I just finished a 1979 low mileage 10k bike that sat for lot of years. I found it easiest to pull the slides out of # 1-3 cyls for removal, I did not listen to you – on carb rebuild because I have been at it a few years, so I had lots of practice taking them on and off. You are 100% right on all your info. I like the line that says you need “General Intelligence” . I did not catch the leak on the fuel O rings at the Plenum – or leaky aftermarket float valves. I worked on these a little in 1977-78 before getting into Hondacars. 40 years later things could happen to rubber that we did not see when the bikes were three years old. I like your advice on using a vacuum gauge for checking the fuel system for leaks, also how you weight the floats. Someone who worked on it before had big pilot and main jets. I had a hard time finding Pilot Jets found that the ones from a Keihin CR starter jet was the same for a #35 – (Sudco # 019-370). I was very lucky to have a factory service manual -Best manual I have ever seen. I used the four O rings that seal the carbs to the Plenum, I have never had this style of O ring go into the groove so nice. On aftermarket carb kits they would pop out and it would always be a major struggle. Yours are the best ever you should be proud. Thanks again for great info and really quality not made in China products – A very satisfied customer Denis Kerechuk. PS thanks also for supporting AHMRA.

  3. Hi, its mike from New Zealand.
    I recently saved 2 gl 1’s 1975, an 2 cb 900 f2’s 1982, one with fairing kit.
    From death by neglect, left out side to suffer the elements, everyone said I was mad an their rubbish ? I have stripped down to frame for powder coating, the f2 with fairing, completely stripped motor an rebuilt, wearable parts with new, except clutch plates, they were ok, obviously been changed, oil was white an rust on meshing gears, but cleaned an polished all, just waiting on chromeing to return to complete an rebuild, had to get sticker set made for bike ( silver an white) couldn’t find transfers for fairing model on net, one thing I cant find is a left hand wing mirror ?The G L ‘s are the worst, one at least (red) was left without carbs on, and came with 2x 2 barrel webber’s, home made mounting stacks an a brown folder 2 inches thick with detailed instructions to convert, the other (black) I managed to get running, badly until fuel flooded number 3 cylinder, so set about rebuilding carbs, had manual, basic instructions nowhere near as good as this site of yours, spent a year, looking for information for problems I encountered, until I found you, none the less had it running ok, have just lifted the needles as per your advice, my question is :- How long should the springs be for the main throttle body ? Many other questions for improving performance, but will start with that one first.
    Regards Mike ( gls right ! Down under )

  4. I have a 1977 Gl 1000A that has not run correct since I bought it 25 years ago(and has been sitting for 20yrs). I recently rebuilt the carbs with the Randak kit and started it up. It is still running rough and it now has a surge after warmup. I noticed that the nylon(plastic seals) that are between the slide cap and the carb body are not thick enough. After measuring they are about .009″ short from sealing. Is this normal or could this be causing the problem?

  5. I have a 1983 Honda Aspencade 1100. It has 49k on it. I have had the carburetors cleaned and tuned on it for the last 3 years. It has been garaged all it’s life. It starts right off. Idles just fine. Takes off in 1st gear just fine and when I shift to 2nd and give it full throttle it bogs down to nothing unless I back off on the throttle. If I slowly take off in each gear it will run up to 70. If I give it full throttle it will just bog down to nothing. If I hold it at 70 and come to a slight hill it will bog down, but if I add a little choke to it I can go up the hill. If I go at 70 and it bogs down on a hill I choke it but the fuel mileage drops very significantly. Maybe I need to take it to a more experienced mechanic.

  6. Curious about 1 float bowl screw that seems to stripout on each carb on the gl1000 carbs. Is this common. Did not crank them too tight. Just one screw hole with very few threads.

  7. I have a 79 wing, someone has had the carbs question is that in front of the float post is a ball bearing in 3 of the carbs, not in the forth, is this normal?? Can I buy that?it doesn’t show up in any pictures or book

  8. Question. Somebody’s brought me a 76 gl1000 set the floats ( someone elase did carb rebuild) here is my issue. Started fine ran nice for a couple minutes then like crap, if you are looking at #1 carb bottom left there is a good bit of drip coming from that corner am i missing thanks somethinh

      1. I appreciate you taking the time to answer my question . I am currently getting my dads 1975 GL 1000 back in running order he purchased it new in 1975 and was the only owner its got 26 000 miles on it , it’s been sitting in the garage for the last 25 years and is in need of some TLC.

  9. Bought a 1983 Aspencade that had been sitting for 5 years, rebuilt carburetors using the Randakk kit. Carbs didn’t look too bad, considering the years. Carefully followed instructions, especially cleaning passageways with compressed air. It won’t run without full choke, and even then, won’t rev above idle. I’ve sent comments that indicate the pilot screw/jet/passageways may be blocked. Not knowing how the bike ran before it was stored aggravates the problem a bit. Any ideas would be greatly appreciated !

    1. Dan,
      Carburetion is a very technical aspect of a multi carburetor engines. When it comes to how the bike performs after the carb rebuild it would be difficult to cover all the possibilities. We suggest you to visit our website and go to the tech blog for pointers. We would also suggest that if the bike will only run with the choke on – you have a lean mixture concern. Check all appropriate possibilities.
      Thank you for your inquiry,

  10. 1983 GL1100I. Are these floats upside down or is it my imagination. Seems all of the carbs I have had experience with over the years, the larger portion of the float billows sat down into the float bowl with the tang at or near the top. These seem to fit just the opposite with the tang near the bottom and the float billows mostly above the tang. Also, I misread some instructions, and tried to remove what I thought was the idle jet with an e-z out. Not sure if I did much damage. Will this be a problem with the idle mixture? Thanks..Ron

  11. Well. I have a 1979 GL1000, is an almost finish project, frustration is just a simple word. when the bike starts up start leaking gas thru the exhaust and thru the manifold. somebody told me is a stuck float. don’t know what to do anymore, I guess look a professional mechanic. Any thoughts?

  12. I’ve recently been told that one must be careful when replacing GL1000 carbs with rebuilt carbs as “The carbs have a small code on the manifold, because there were small differences each year. They all work, but performance can suffer if they aren’t for the proper year. ”
    I don’t think this is true but wanted to confirm/deny it.

    1. Yes. There are different carb codes for each model year of GL1000s. There are small but important differences. Generally, ’75-’77 carbs interchange with each other. Ditto for ’78 and ’79 carbs.

    1. Those are emissions limiter caps. They are designed to “limit” the available range of idle mixture screw adjustment. Unless you are doing a concours restoration, they can be removed and tossed. They have to be removed anyway to allow the idle mixture screws to be unscrewed fully during an overhaul.

  13. is there a easy way to take off the rubber boots off of the carb intake tubes? it seems as though they are glued on. I am aware of your trick to soak them in warm/hot water before slipping them on, but how do they come off? vrey hard.
    thanks for any help.

  14. I used Randakks kit. Took nearly 4 weeks to do the job right. I had to order a second rack to replace some questionable parts so that tacked on some time. I took a day for the rebuild and install. It took me the entire day of focus to ensure everything was done correctly. I knew that when I put the carb rack on the bike, if the bike was still not running correctly, there would be no chance it was the carbs. I put the carbs back on the bike and sure enough, still hard starting, no idle, wont run without full choke. My forum suggested that I had botched the job, but I knew better. I started checking the ignition system. One of the points was not adjusted to open at all! It was just held hard shut. So… I made a small adjustment and the bike fired right up with no choke. I dialed back the idle and she purrs at about 1k rpm. I finally was able to ride the bike for the first time since I purchased it. What a great feeling of accomplishemt. By the way, this was the first carb I have ever worked on. I still need to verify the timing and do a carb sync to make sure every thing is perfect, but I am over the hump. I also did the off air idle fix, super easy to do.

    Take your time. Do your homework. Use copious amounts of air. Don’t assemble until you have the time to do it until its done. Dont assemble until you are positive the carbs are clean as they can be. Don’t cut any corners. Buy Randakks video. If I can do it, so can you!

  15. I have a low-mile (24K) 75 GL1000, that I recently purchased from an older gentlemen. The bike is in very good condition but due to his age and health the fuel-system was neglected. I removed the tank, cleaned it, changed the fuel-lines and filter. I have not taken the fuel-pump apart as it is pushing fuel. I have spark and the bike really wants to start but it isn’t getting fuel (plugs are dry.) I am reading your Posts and am in the process of deciding if I should buy your kit or have the job done professionally.
    MY QUESTION IS THIS: When I crank the engine fuel squirts out of two pinholes on either side of the fuel-pump. Is this normal? Is this an indicator that the carbs are not accepting fuel and are therefore causing back-pressure? Are they air-vents? I can’t find any information regarding this matter.

  16. After using several of Randakk’s kits, I’ve had excellent results from every rebuild. Helping many other enthusiasts with their carbs, I’ve found many errors and incomplete cleaning. By following the video, and Honda manual, and using correct OEM products, is essential in doing it right the first time.

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