YZ250G carby advice

[YZAT252]

Hi guys, need your help. I just bought a new Mikuni 38mm round slide carb off Mikuni Oz in Townsville for my 250G. When I tried to fit it I found it is about 15mm longer than the old one in the flange that goes into the air box and won't fit because there is a lip in the air box stopping it going in too far, I can either grind the lip out on the air box or cut 15mm off the carb but not too keen on either option. Anyone else had the same problem? I am sure someone else out there has replaced their carby on one of these? All comments welcome. Cheers Craig

[oldyzman]

Yep,
Cut off the back of the carby...
Brett

[YZAT252]

Thanks Brett, not sure I would feel confident doing that myself, anybody recommend someone in Brisbane who would handle doing that neatly?

[Simo63]

Thanks Brett, not sure I would feel confident doing that myself, anybody recommend someone in Brisbane who would handle doing that neatly?

I was going to volunteer to do it for you but then noticed you said the word "neatly" so thought I had better leave it to someone else

[YZAT252]

Ha ha thanks Simo, you have plenty of experience with these, you agree that cutting 15mm off the carby flange is the answer?

[Paul552]

Put it up in a lathe a face it off

[Simo63]

Ha ha thanks Simo, you have plenty of experience with these, you agree that cutting 15mm off the carby flange is the answer?

Just to clarify, when you say carby flange, do you mean the rear of the carby? 

Assuming you do mean the rear, tO be honest  mate i would measure and make sure you need the full 15 mm off.  The original airbox boots on these bikes usually shrink back a bit with age so if you can take up some of that shrinkage with a longer carb mouth then take this opportunity.

Also when cutting the end off, you need to spend the time smoothing the bell mouth inlet out.  Not suggesting you go the whole smooth bore route but certainly tapering the inlet and smoothing the airflow.

Just remembered, you might be limited with what you can cut off due to the placement /depth of the breather holes.

[YZAT252]

Yes mate, the rear of the carb, maybe start at 10mm but no way it will fit the way it is because the ridge inside the rubber in the air box stops it, but maybe it can squeeze another 5mm, have you ever had to change one on your bikes and found the same problem?

[Simo63]

Yes mate, the rear of the carb, maybe start at 10mm but no way it will fit the way it is because the ridge inside the rubber in the air box stops it, but maybe it can squeeze another 5mm, have you ever had to change one on your bikes and found the same problem?

No I've not had that problem mate

[DR500]

easy to hacksaw off.just mark a line all way round and take your time.

[tony27]

Even with the standard carb it's a tight squeeze, taking it out certainly tests out your swearing vocabulary.
I shortened the back of mine for the CZ to stop it hitting the front of the airbox, if you use a lathe it would pay to turn up a plug so the body doesn't collapse in the jaws when tightening it up which leads to it climbing out. I ended up taking the slide out & clamped it that way in the vice on the mill, still heaps of parallel section left before you get to the start of the bellmouth & air passages
Hope that makes sense

[oldyzman]

If you put it in a lathe!
Plug the end your gripping in the chuck so you can grip it tight as I have thrown a VM across the room before

[YZAT252]

Well I can report that I spoke to Tom Hatrick from Mikuni and he said ok to cut it down which I did. Plugged holes up with blue tack, stuffed a rag down the throat, wrapped it in glad wrap ans sawed off 15mm with a hacksaw. Dressed it with a file, carefully removed filings, rag, blue tack and blew a bit of air through. Fitted it tonight, started second kick! Give it a run on Sunday and see how she goes, thanks everyone for your help and advice!