Chris
I'm pretty sure the boot you are describing is part 510-13555-02-00. Dimensions are the same as the one on my IT400C (76 model). I have one spare in ok condition, some small cracks. Problem with them is they begin to perish and get hard and crack. They then let air in and the bike runs lean.
You can have my spare if you like. Maybe do COD on postage. Also Fernando from Husky Parts is making aftermarket carby rubber boots now. He may be able to help.
I'll pm you some details and email a photo if you like. I also have one off a DT400 which I bought thinking it would be the same as the IT. It has a 38 mm bore (as oppsoed to 40) and 74 x 68 bolt centres. + reed block.
They come up regularly in the states on ebay, can be pretty pricey though ~ $130ish.
Andrew
Thanks Two Dogs. I'll see if I can find one for a reasonable price before I take your spare. Who knows, you might need it.
I found one on ebay.
They want $232 USD!!!! MSRP is only $63.62 USD. Outrageous!!
According to them, it also fits:
•MX250B 1975 250 MX250 Off-Road
•MX400B 1975 400 MX400 Off-Road
•YZ250C 1976 250 YZ250 Competition Motocross
•YZ400C 1976 400 YZ400 Competition Motocross