400f carb bored?

I've still been tracing the whole carb issue on this bike but this caught my eye today, is seems like it was bored to an oblong shape, I will mic it tomorrow. But this doesn't seem factory to me


I just measured it it measures 41mm on the vertical axis and mid way up on the horizontal it measures 39mm so with this home made bore job on stock jetting would cause it to spit sputter and pop like it is now? Also after this discovery I feel like it would be wise to go to a newer 450 carb correct?

Edited by Buzzy613

It would be anyway.  The bore likely has nothing to do with how it's running, though.  The old FCR's get to be a huge pain in the butt when they get worn and/or develop internal problems.

I found an 03 450 carb throttle cable and hotstart, I know in multiple forums you stated 05+ but I'm unsure if the 03 will help much like the 05+

The '03 will work, and quite a bit better than the original.  The downside to the '03-'04 carbs is that they don't have a leak jet, which takes one tuning tool off the table, but that's not a big deal, really.

Alright thank you so much, I know this question gets beat to death but past threads only have so much information

Would a 40mm fcr from a crf work if I swaped the needle out for the stock yz450f? And tool the time to jet it?

Probably, but I don't know about the throttle cables, nor whether the main air jet and main nozzles are the same.

Well I thinknits found my issue the vacuum release plate has a big hairline crack in it, so im going to order a new one and a rebuild kit for this carb, since there is no 450 carbs anywhere on ebay


Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now