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Top Honda GL1000 Carb 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-laws and neighbors. Avoid these mistakes if you tackle a rebuild yourself.

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.

6. 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.

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!

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 stongly 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 stongly 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 Problem Tech 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." See details below in Tech Tip section. 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 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 assys (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 affect, 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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