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I had to deal with a few issues last night while replacing the airbox after renewing the fuel lines on my GS850G, and it occurred to me that some of this might be useful info for other folks.
Please add your own questions and airbox protips!
Fixing Warped Airboxes:
The front of the airbox where it connects to the carbs tends to bow in over time and can make getting the inner two boots completely onto the carbs nearly impossible.
On some bikes, like the 1100E, you can use a wooden stick or something similar inserted from the rear to push forward against the middle of the airbox to get everything lined up; hold the stick until you tighten the boots. On other bikes, like the shafties, you don't have access to do this.
A more reliable/long term solution is to remove the airbox, remove the carb/airbox boots, and use a heat gun (a hair dryer probably isn't hot enough) to soften the plastic slightly. Push/pull the plastic into place so it's flatter and hold it until it cools again. (Same goes for any GS airbox.) Be careful, keep the heat moving, and go slow so you don't make things worse. Plastic also expands and contracts when heated and cooled, so take it slow until you understand how the material responds.
I normally just do this with my hands with gloves on or protected from the heat by a rag. If you're a crafty sort, perhaps you could come up with some sort of jig or plate to hold the row of carb holes straight and level as they cool.
Replace the Boots and Clamps
Should be first in the list, but replace your airbox/carb boots and the clamps if you haven't already, and if they're available from Suzuki. You will be astonished by how much these have shrunk over time; many folks have been convinced they received the wrong parts. Makes airbox installation about 1,000,000% easier. If your old clamps are in good shape, you don't really have to replace them, but most have been chewed up by non-JIS screwdrivers and bent over the years; new clamps will work much better.
Same goes for other rubber tubes, clamps, etc. If replacements are available, buy them and make your life easier.
Fixing Warped/Damaged Boots
Sometimes despite your best efforts, you find that a carb/airbox boot has folded over last time it was installed. The damage can look insurmountable, and sometimes it is. But quite often, you can undo a surprising amount of damage and re-shape the boot so it's usable again. You can fix badly folded areas, but if the boot has torn or split, you'll definitely need to replace it.
First remove the boot from the airbox. Next, find something round, metal, and sturdy that's the same or close to the size of the carb inlet. I usually use an old bearing or bearing race since that's what I have lying around.
Next, heat up the boot with a heat gun. Go slow; you want to soften it, not melt it. You need a heat gun; a hair dryer isn't hot enough. As soon as you can, gently place the boot over your round thing and add the clamp. Gently massage the damaged area into shape with your fingers using a rag to protect yourself from the heat. Use the edge of the clamp to help persuade the edge back into shape. Don't tighten the clamp until everything looks good. Very lightly tighten the clamp, ensuring the boot stays fully seated on the round thing. Set it all aside to cool.
Installing and Removing Insanely Tight Airboxes
This gets model-specific, but many principles can apply broadly.
On the 1100E models, the rear airbox covers the battery and is a royal pain in the giblets to remove and replace. You can make this far, far easier by heating one specific corner of the airbox and pushing it in slightly using a flat surface. I don't remember which corner this is, but it's the corner that always hangs up and has a bunch of scars on it from all the yanking over the years. The amount of reshaping you need to do is quite minor. Go slow; you want to soften the plastic, not melt or burn it.
On many of the smaller GS models like the twins the airbox seems impossible to remove and replace. The "secret" many miss is to get the plastic inner rear fender out of your way. You don't have to remove it; just remove any mounting screws for the fender, then pop it loose from its mounts. This allows the fender to move back a bit, giving juuuuust enough clearance for the airbox to move back and wiggle out.
Seal Your Airboxes
Airbox snorkels, lids, and seals seem to have gone missing on a lot of bikes, and if you don't realize there are parts missing it's impossible to get the carburetion right.
For example, shafties NEED the snorkel on the back of the airbox to run right. And on all bikes, you have to ensure that air can only enter the airbox where and how it's supposed to and that dirty air can't bypass the filter. Use weather stripping or whatever to seal covers, lids, and around the filter as needed. Sealing the airbox is a well-known rite of passage for shaftie owners.
Same for airbox lids on other models. Many have been lost over the years, and many have been removed and discarded by ignorant previous owners looking for "more airflow". (If you increase airflow, you also have to rejet, the step most people skipped.) Some misguided folks even cut holes in their airboxes... the '80s were a strange time.
Aside from some idle/off-idle leanness easily sorted by richening the idle mixture screws a tad, all GS models ran and carbureted beautifully straight from the factory. Before you start farting around with pods, pipes, cutting holes, etc. you'll do much better if you can get the bike back to factory condition as a baseline.
Please add your own questions and airbox protips!
Fixing Warped Airboxes:
The front of the airbox where it connects to the carbs tends to bow in over time and can make getting the inner two boots completely onto the carbs nearly impossible.
On some bikes, like the 1100E, you can use a wooden stick or something similar inserted from the rear to push forward against the middle of the airbox to get everything lined up; hold the stick until you tighten the boots. On other bikes, like the shafties, you don't have access to do this.
A more reliable/long term solution is to remove the airbox, remove the carb/airbox boots, and use a heat gun (a hair dryer probably isn't hot enough) to soften the plastic slightly. Push/pull the plastic into place so it's flatter and hold it until it cools again. (Same goes for any GS airbox.) Be careful, keep the heat moving, and go slow so you don't make things worse. Plastic also expands and contracts when heated and cooled, so take it slow until you understand how the material responds.
I normally just do this with my hands with gloves on or protected from the heat by a rag. If you're a crafty sort, perhaps you could come up with some sort of jig or plate to hold the row of carb holes straight and level as they cool.
Replace the Boots and Clamps
Should be first in the list, but replace your airbox/carb boots and the clamps if you haven't already, and if they're available from Suzuki. You will be astonished by how much these have shrunk over time; many folks have been convinced they received the wrong parts. Makes airbox installation about 1,000,000% easier. If your old clamps are in good shape, you don't really have to replace them, but most have been chewed up by non-JIS screwdrivers and bent over the years; new clamps will work much better.
Same goes for other rubber tubes, clamps, etc. If replacements are available, buy them and make your life easier.
Fixing Warped/Damaged Boots
Sometimes despite your best efforts, you find that a carb/airbox boot has folded over last time it was installed. The damage can look insurmountable, and sometimes it is. But quite often, you can undo a surprising amount of damage and re-shape the boot so it's usable again. You can fix badly folded areas, but if the boot has torn or split, you'll definitely need to replace it.
First remove the boot from the airbox. Next, find something round, metal, and sturdy that's the same or close to the size of the carb inlet. I usually use an old bearing or bearing race since that's what I have lying around.
Next, heat up the boot with a heat gun. Go slow; you want to soften it, not melt it. You need a heat gun; a hair dryer isn't hot enough. As soon as you can, gently place the boot over your round thing and add the clamp. Gently massage the damaged area into shape with your fingers using a rag to protect yourself from the heat. Use the edge of the clamp to help persuade the edge back into shape. Don't tighten the clamp until everything looks good. Very lightly tighten the clamp, ensuring the boot stays fully seated on the round thing. Set it all aside to cool.
Installing and Removing Insanely Tight Airboxes
This gets model-specific, but many principles can apply broadly.
On the 1100E models, the rear airbox covers the battery and is a royal pain in the giblets to remove and replace. You can make this far, far easier by heating one specific corner of the airbox and pushing it in slightly using a flat surface. I don't remember which corner this is, but it's the corner that always hangs up and has a bunch of scars on it from all the yanking over the years. The amount of reshaping you need to do is quite minor. Go slow; you want to soften the plastic, not melt or burn it.
On many of the smaller GS models like the twins the airbox seems impossible to remove and replace. The "secret" many miss is to get the plastic inner rear fender out of your way. You don't have to remove it; just remove any mounting screws for the fender, then pop it loose from its mounts. This allows the fender to move back a bit, giving juuuuust enough clearance for the airbox to move back and wiggle out.
Seal Your Airboxes
Airbox snorkels, lids, and seals seem to have gone missing on a lot of bikes, and if you don't realize there are parts missing it's impossible to get the carburetion right.
For example, shafties NEED the snorkel on the back of the airbox to run right. And on all bikes, you have to ensure that air can only enter the airbox where and how it's supposed to and that dirty air can't bypass the filter. Use weather stripping or whatever to seal covers, lids, and around the filter as needed. Sealing the airbox is a well-known rite of passage for shaftie owners.
Same for airbox lids on other models. Many have been lost over the years, and many have been removed and discarded by ignorant previous owners looking for "more airflow". (If you increase airflow, you also have to rejet, the step most people skipped.) Some misguided folks even cut holes in their airboxes... the '80s were a strange time.
Aside from some idle/off-idle leanness easily sorted by richening the idle mixture screws a tad, all GS models ran and carbureted beautifully straight from the factory. Before you start farting around with pods, pipes, cutting holes, etc. you'll do much better if you can get the bike back to factory condition as a baseline.
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