eBay seller "Incendiary Concepts 78-80 CB400A CB400T Carb Boot" (airbox boot)

Maraakate said:
Chris bought them. They are hardened junk and rough textured. I wouldn't use it.
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Glad you got to check them out Frank. I wondered just how flexible they could be, although I guess in a pinch they might be okay in that format strictly on the airbox side.
 
Yeah, I was not impressed. I actually have them still sitting in a box. I'll get a close-up picture, but if you look carefully in the auction photo you can see all the lines from it. They're slightly more pliable than some worn, but stored OK, boots.

Honestly, if you have hardened boots but they are not ripped then take a heat gun (not a hair dryer!) and work them back and forth slowly for a couple of minutes and they will be pliable enough to seat the carbs. New air box bands are critical after you disturb them.

A lot of problems I see is stretched intake and air box boot "bands" as Honda calls them. I dislike the worm gear clamps and will undo them on any bike that comes to me. They tend to dig into the rubber and causes problems later. The bands are still available. The aftermarket bands tend to be hit or miss. Sometimes they just don't get as tight as the real ones. No idea on their longevity.
 
Hey everyone — I'm Jacob, the seller behind Incendiary Concepts. I actually came across this thread and wanted to reach out directly.

The feedback here is genuinely appreciated, even if it's not glowing — it's exactly the kind of thing that helps me improve. I'm currently working on an updated version of the CB400 airbox boot and would love input from people who actually know these bikes.

A couple questions if you're willing:
- What are the biggest pain points with the current design? Fitment, flexibility, material texture, clamp compatibility?
- Is there anything about the OEM boot that you'd want replicated?

I'd also love to send a set of the updated boots to anyone willing to do a real-world test fit and give honest feedback. No obligation to say anything positive — I just want to know if it actually works.

Feel free to PM me here or through eBay. Thanks for the honest discussion.
 
Maraakate said:
Yeah, I was not impressed. I actually have them still sitting in a box. I'll get a close-up picture, but if you look carefully in the auction photo you can see all the lines from it. They're slightly more pliable than some worn, but stored OK, boots.

Honestly, if you have hardened boots but they are not ripped then take a heat gun (not a hair dryer!) and work them back and forth slowly for a couple of minutes and they will be pliable enough to seat the carbs. New air box bands are critical after you disturb them.

A lot of problems I see is stretched intake and air box boot "bands" as Honda calls them. I dislike the worm gear clamps and will undo them on any bike that comes to me. They tend to dig into the rubber and causes problems later. The bands are still available. The aftermarket bands tend to be hit or miss. Sometimes they just don't get as tight as the real ones. No idea on their longevity.
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Hey Maraakate, just wanted to follow up on my post above. Would really value your input specifically, since you clearly have deep experience with these bikes and the airbox boot fitment issues firsthand.

If you're willing, what are the biggest pain points you've seen with the current design? Fitment, flexibility, clamp compatibility, anything really. And is there anything about the OEM boot you'd want replicated that aftermarket versions tend to miss?

Feel free to PM me here or through eBay. Really appreciate the detailed write-up in this thread, it's exactly the kind of knowledge that helps me build a better product.
 
It's not pliable. It feels like plastic. Feels cheap.

Considering this is an "emerging technology" I would like it tested over a long period of time. Especially against gasoline vapours to ensure it will not distort. Having it exposed to UV and more specifically sitting outside for a long time. I've seen many aftermarket boots (airbox and insulators) where they seem OK at first but distort by collapsing, cracking over time (UV exposure), or they enlarge from the vapours. Enlargening seems to happen the most with very cheap ones. How does it hold up to being persuaded with a heat gun? Sometimes this is necessary for some bikes to fit them on the carbs. Because it's 3D printed and you can see the lines I'm not even sure how air tight it would be in a vacuum which is critical for this application.

Honestly, for me to use it and recommend it to any customer bike I'd work on it would have to be battle tested for a year and exposed to sitting outside for a year because there's plenty of these boots out there that have sat in junkyards for 30 years and are still usable.

I'm very very critical about this kind of stuff. I'm not sure if 3D printed parts would hold up over time for something like this. It wouldn't be an issue if it was 5 minutes to swap these boots out, but to do it properly is about 45-60 minutes. A bit faster if you've done it many times like I have. I've looked into getting molds made up before and there's a guy who makes many for XS650 and similar bikes. When I asked him a price he basically told me if I had to ask I couldn't afford it and then I asked him his MOQ and he just stopped answering me.
 
Maraakate said:
It's not pliable. It feels like plastic. Feels cheap.

Considering this is an "emerging technology" I would like it tested over a long period of time. Especially against gasoline vapours to ensure it will not distort. Having it exposed to UV and more specifically sitting outside for a long time. I've seen many aftermarket boots (airbox and insulators) where they seem OK at first but distort by collapsing, cracking over time (UV exposure), or they enlarge from the vapours. Enlargening seems to happen the most with very cheap ones. How does it hold up to being persuaded with a heat gun? Sometimes this is necessary for some bikes to fit them on the carbs. Because it's 3D printed and you can see the lines I'm not even sure how air tight it would be in a vacuum which is critical for this application.

Honestly, for me to use it and recommend it to any customer bike I'd work on it would have to be battle tested for a year and exposed to sitting outside for a year because there's plenty of these boots out there that have sat in junkyards for 30 years and are still usable.

I'm very very critical about this kind of stuff. I'm not sure if 3D printed parts would hold up over time for something like this. It wouldn't be an issue if it was 5 minutes to swap these boots out, but to do it properly is about 45-60 minutes. A bit faster if you've done it many times like I have. I've looked into getting molds made up before and there's a guy who makes many for XS650 and similar bikes. When I asked him a price he basically told me if I had to ask I couldn't afford it and then I asked him his MOQ and he just stopped answering me.
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I've made several hard to find parts for my bikes with a 3d printer. I've made them out of TPU and PETG .

I made an replica air box and intake boot for my old Honda moped. I've put about 3000 miles on the bike over about 2-ish years. They've held up well so far aginst gasoline. For sealing issues I use fuel system gasket dressing.

That being said they're fine for something I made in an afternoon for $1, but I'd really struggle paying for a 3d printed part.

There are tricks for smoothing out the lines, but it's just not the same as an injection molded part.
 
Yeah, I hear you there. For DIY on this sort of thing it makes more sense.

To be fair, a moped (what was it a Hobbit or those NU50 "no-peds"?) is a lot more forgiving and easier to tune. I just have had so much bad luck with aftermarket rubber components that are for the intake system on any of these vintage bikes. There's those aftermarket CM400T, etc. boots and they do work OK. They just seem to start cracking and sagging after about 3 years. The originals lasted for 40 years. Kind of unacceptable in my opinion. And those are molds. So that means whoever is making it is cheaping out on the material.
 
I don't really have any chips on the table here as I do not own a 400T/400A, but I'm generally a fan of the idea of quality replacement parts being created to fill gaps in the current supply of parts for our vintage motorcycles.

Perhaps a good starting point would be a discussion of the materials being used to print the manifolds. The material must be printable, it must be chemical resistant, it must be somewhat heat tolerant, sturdy, flexible, and it must either be sealed or naturally capable of creating an air-tight seal. I suppose an ability to withstand annual temperature fluctuations and prolonged UV exposure would also be important.

What research was done in the selection of material? What material is being used currently? Are there more suitable materials that could be used instead?
 
I'd prefer it to naturally seal as opposed to using some sort of goo to "help" it. It's just another failure point down the road.
 
Great feedback everyone, this is exactly the kind of discussion that helps improve the product. A few things worth addressing:


To clarify on material: current boots are printed in TPU, not rigid plastic, so the UV and ozone concerns are less of an issue than they would be with ABS or PLA. That said, the feedback here has pushed me to look further, and I'm planning to transition to TPE for the next revision. TPE is chemically closer to OEM rubber than TPU, has better long-term flex fatigue resistance, and seats more naturally against aluminum and plastic carb flanges.


On fitment and installation difficulty, I'm also reducing wall thickness in the next revision to make sliding them onto the carb and airbox significantly easier without sacrificing the seal. The current version fits, but I want installation to feel closer to an OEM replacement rather than a fight.


For anyone skeptical about longevity compared to injection-molded parts, that's a fair concern and I won't oversell it. What I can say is that these exist specifically because OEM boots are discontinued or priced out of reach, and a well-printed TPE boot that lasts a few seasons is more useful than no boot at all. I'm also looking for beta testers willing to run these and report back on long-term durability.


If anyone wants a set to test, reach out. Honest feedback is worth more to me than a sale.
 
Update: New TPE Carb Boot Revision – Beta Testers Wanted

Hey everyone, following up on the feedback from this thread (thanks again to Maraakate, ecefour, stl360+450, and others for the detailed input).

Here's what's changing in the next revision:

Material switch to TPE
Moving from TPU to TPE for this revision. TPE is chemically closer to OEM rubber, has better long term flex fatigue resistance, and seats more naturally against aluminum and plastic carb/airbox flanges. Should also hold up better to gasoline vapor exposure and UV over time compared to the current TPU boots.

Reduced wall thickness
Tightened up the wall thickness so the boots slide onto the carb and airbox more easily without losing the seal. Goal is for installation to feel like a true OEM replacement, not a fight to get them seated.

Print quality
Continuing to refine layer line smoothing on the sealing surfaces, aiming to get as close to an injection molded feel as possible within what's realistic for printed parts.

Looking for testers
Since the real test is long term durability (heat, fuel exposure, UV, time), I'm looking for a few people willing to run a set on their bikes and report back after a few months/seasons of use. If you're interested, PM me here or reach out through eBay.

Appreciate everyone keeping this discussion honest, it's directly shaping the product.
 
Are you able to share pictures of the new design?

And do I recall correctly that you have a couple of related motorcycle projects? One 400T and one 400A? It might improve the visibility of your design if you created a project thread to document their use on your machines.

I will mention a few regular contributors with appropriate bikes just to make sure they are aware of this thread and the most recent call for beta testers: @esh21167, @esmith250624, and @79CM400A.

Addendum: I may have misunderstood previously about how the term "carb boot" is being used here. Is the product for the air box manifolds only or also the carb boots to the head?
 
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IncendiaryConcepts said:
Update: New TPE Carb Boot Revision – Beta Testers Wanted

Hey everyone, following up on the feedback from this thread (thanks again to Maraakate, ecefour, stl360+450, and others for the detailed input).

Here's what's changing in the next revision:

Material switch to TPE
Moving from TPU to TPE for this revision. TPE is chemically closer to OEM rubber, has better long term flex fatigue resistance, and seats more naturally against aluminum and plastic carb/airbox flanges. Should also hold up better to gasoline vapor exposure and UV over time compared to the current TPU boots.

Reduced wall thickness
Tightened up the wall thickness so the boots slide onto the carb and airbox more easily without losing the seal. Goal is for installation to feel like a true OEM replacement, not a fight to get them seated.

Print quality
Continuing to refine layer line smoothing on the sealing surfaces, aiming to get as close to an injection molded feel as possible within what's realistic for printed parts.

Looking for testers
Since the real test is long term durability (heat, fuel exposure, UV, time), I'm looking for a few people willing to run a set on their bikes and report back after a few months/seasons of use. If you're interested, PM me here or reach out through eBay.

Appreciate everyone keeping this discussion honest, it's directly shaping the product.
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Hey! I’d like to beta test your airbox boots… sorry I’m a new member and can’t PM yet, but if you PM me I believe I can respond. Thanks
 
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