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Flatslides too big for intake boots ?


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Good day everyone, just received my rs38s last week while on honeymoon, got home yesterday and tried mocking them up on my 748 dot*head which has 1100 boots and they wont go in ! I plan on putting them on my 1127 for the moment until the dot*head is finished but im guessing im gonna face the same problem, so what do you guys do to make them fit ?  




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I would assume the 1100 intakes are from a K or L model fitted with 36mm CV's. The M & N models had 40mm CV's. Short stroke 750's had the 38mm CV's. So you have choices - a) Dremel out the 36mm boots to take the 38mm carbs - messy and don't cock it up as they'll be fit for nowt. b) Find some 40mm boots but they'll take more tightening of the clamps than is healthy which can cause the carbs to fall out! And c) Find some 38mm boots but these result in different angle of the carb bank that tends to interfere with fuel taps etc. Sometimes if the 36mm boots are new / really soft they can be stretched enough to accept the 38mm inlets - usually a ratchet strap can be used to pull the carb rack into the boots - either way its a PITA!

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Final answer xD :

BST38 and BST40 are the same size on both the intake pipe side and airbox side, and are bigger than the BST36 and 34

RS36 and 38 are the same outer diameter sizes, and are smaller in outer diameter than the BST38 and 40 (RS racks are lighter than BST, i guess that plays a part in why)

BST36 pipes are needed for RS36 RS38

I fitted a RS38 set on my 1127 and i needed the following pipes, since the original 40 pipes were too big





These are the 1100R BST36 intake rubbers. And the part numbers should be moulded in each pipe to check origin and fitment. Those carbs have the same diameter as RS38s. No dremeling required.

Edited by Joseph
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They are a pig to fit even onto the new 36mm pipes however that is not due to difference in diameters (since RS38 is the same as BST36) but due to the fact that spacing is slightly off (so that the RS also fit some Kamamazaki bikes), so i did indeed use help from a hair dryer and a rat shit strap

Edited by Joseph
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If there is a step, and there could be a small one, because even a stock head with its stock boots you will find the alignment is not perfect, thats where the Dremel can be used.

But the 36 boots are no question the ones you need for proper fitment of an RS38 rack


Edited by Joseph
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But thats a 38mm carb or am I mistaken ?

A few dimensions :

BST 36 carb spigot OD : 42mm

BST 38 carb spigot OD : 46mm

RS 36 and 38 spigot OD : 42mm


how can BST38 rubbers for carbs with +4mm OD be the best fit, when rubbers for carbs with the same OD are available ?

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I/d of my 750 l/m rubbers is 42mm and rs 38s go in perfectly. I have 2 sets of rubbers and they both all measure up at i/d 42mm. I have a set of 750 l carbs and the outer wall thicknesses are definitely not 4mm, which is chunky to say the least. If this is the case, that would be double the wall thickness of RS 38s and the same as RS 34s.

I have relatively easy access to the rubbers but my carbs are in a box under 2 tons of crap but I will dig them out and post pics when I can :).

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What is the spigot OD of the L carbs you have then ? 

I never said the spigot wall was 4mm, i said that the overall difference of diameter between the 38 and 36 BST is indeed 4mm.

i feel that what i state is clearly explained but maybe i can improve.

Anyways, what needs to be measured is the carburetor, not the rubber, since the rubber is made taking in account allowance for snug fitment, (and rubber is more prone to shrinking with age than aluminium xD)

The measures i posted previously are all correct and backed by specs, and indicate what rubber pipes are required in order to properly convert to RS carbs depending on which version one plans on using


Edited by Joseph
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46 0/D - 38 i/d = 8, /2 = 4, which is how the 4mm wall thickness is calculated :). If a 38 mm carb has an OD of 46mm, then the wall thickness of the spigot must be 4mm all round. The only rubbers I am aware of anywhere near this big are for BST40s from 1100 m/n models.

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What rubbers o you have already ? That you say do not to fit the RS ?

I've asked that question twice already.

What reference is moulded in the rubber ?

I've given absolutely all the info required on what to use and how to ease fitment. 

So, what do you have currently at hand ? No need to look for the 40 rubber bits since as i have explained now multiple times, they are too big

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KCR JCP 13110 40co

KCR JCP 13120 40co

KCR JCP 13130 40co

KCR JCP 13140 40co

These rubbers are too small for the carbs and i dremeled them yesterday just enough for a snug fit, also they needed lots of modification to align perfectly to the intakes


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