How important is it for the carb boots to be so tight?

[Syscrush]

Hey all.

The carb boots on the CBX are famously tight, with advice for removal and installation including the use of prybars, 2x4s, ratchet straps, and probably most importantly the use of a heat gun to get the rubber smoking hot.

I am in the design phase for custom throttle bodies to replace the OEM carbs. They will install in place of the OEM carbs, which will allow the inclusion of the entire OEM intake tract, plus the OEM throttle linkages and cables.

The bad news is that I intend to fabricate these throttle bodies from a material that is unlikely to withstand the heat required to get the rubber boots smoking hot.

The good news is that I have complete control over the final shape and dimensions of the completed throttle bodies. It's hard for me to understand why they have to be as tight as they apparently do. This might be an unanswerable question, but how much of the difficulty with removal and replacement is due to tightness, and how much is due to the amount of deformation required because of the V-shape of the bank of carbs and the boots that receive them? If the shape or size of the outlets of the carbs/throttle bodies was changed to make removal and replacement easier, would it even make a difference?

Thanks for any advice or insight on this.

[Dynamohum]

Tight is relative. They only have to be tight enough to seal. The clamps do a lot of that work. As they age and withstand heat over the years they seemingly turn ceramic hard and then they’re famously hard to remove. Installing new soft boots isn’t all that hard.

[CBX-tras]

I've been using these for years, about 1/2 the price of stock clamps and they're made of STAINLESS STEEL! (They don't come polished).

https://www.aircraftspruce.com/catalog/ ... /055-9.php

55mm for the boots, 60mm for the airbox. Available in many sizes.

[Larry Zimmer]

While I'm far from a wizard, Phil, I would say the carb boots should be 1 or 2 mm 'tight' on the diameter. A little stretch is good/necessary. The clamps don't so much seal as they just keep things from coming apart. If the clamps were to distort the boots any, there will be a 'buckle' effect that would, then, be a leak. My numbers are a WAG on my part. I've never bothered to measure new boots to confirm. Maybe someone has a new boot and can measure it for us. Bottom line, though, they do need to be snug.
The use of blasting powder to remove old ones is a matter of aging and heat. Generally, I've found that blasting caps are sufficient! :) Maybe air hammers. (Said the smart ass, here)

[Rick Pope]

Perhaps there's a market for the boots to made from a silicone material, that would be more heat resistant, thus less prone to hardening. Just look under the hood of newer trucks and heavy equipment. Nearly all hoses are now silicone based. Especially turbo hoses which get a lot of heat.

[bobcat]

Maybe Viton boots ?

[CBX-tras]

My test for checking the clamping effort is this for stock clamps:

If you push in the screw head with a driver and the clamp rotates, it's loose.
If the clamp ends are butted together, you need new boots.

As simple as that.

[NobleHops]

While we're on the subject of insulator clamp tightness, new ones ALWAYS need to be re-tightened up after a heat cycle. Do not neglect this.

[Larry Zimmer]

My test for checking the clamping effort is this for stock clamps:

If you push in the screw head with a driver and the clamp rotates, it's loose.
If the clamp ends are butted together, you need new boots.

As simple as that.

YUP!!

[Syscrush]

Perhaps there's a market for the boots to made from a silicone material, that would be more heat resistant, thus less prone to hardening.

I've been thinking about silicone replacements for these boots a lot. I have the means to 3D print some molds and cast my own silicone replacements that match the dimensions of the originals.

[Larry Zimmer]

That would be most interesting, Phil. Keep us posted.

[Syscrush]

Today it was pointed out to me that silicone is not a good material for applications with gasoline exposure. I assumed it would be fine because I've seen silicone couplings used in the intake plumbing of so many turbocharged engines, but it didn't really occur to me that none of them are exposed to fuel, as they're all upstream of the injectors.

[CBX-tras]

The rack has no other support other than the boots. A too soft of material will eventually fail with separation.

[Syscrush]

The rack has no other support other than the boots. A too soft of material will eventually fail with separation.

I was wondering about this. With the OEM intake all intact, the rack of carbs is suspended between the cylinder head on the fore side and the airbox on the aft side, correct? And the airbox is fastened to the frame.

[CBX-tras]

The airbox is plastic, the bellows between the carbs and airbox is flexible and the bracket on the airbox is held on by 2 screws into plastic.
Not a lot of mechanical support there.