Wrong size carbs?!

[Large]

Hello everyone

Here's my problem, I recently bought a cheap xs400 off ebay for a custom project but it's a bit of a mess, I think the frame is from a 250 and the engine a 400 which is not a major problem but I was cleaning the carbs and checking the float heights and I think someone has fitted a pair of 250 carbs to the 400 engine.

Is this going to cause me a major problem? Do I need new carbs or can I tweak them?

Any help please

cheers Large

 

[HoughMade]

Curious- what makes you think the carbs are from a 250? What year is the engine?

 

[xschris]

how about some pics.

 

[Large]

I'll try and get some pictures on here but there were a few tell tales, 1. the floats were set at 26mm and not 32mm which is too big to be a mistake 2. there should a valve in the carb mouth but there’s not 3. I checked it against picture on Google and they are definitely different. The bike has definitely had a shady past.

So any ideas?

 

[bikerbob]

Float height in the manuals are know to be wrong. I believe the manual says 32 but 26 or 27 is correct.

 

[drewpy]

250 carbs size are 32mm 400's are 34mm

whats the frame number?

 

[bcware]

34mm for rubber floats? 26mm for brass floats. Pics!

 

[drewpy]

BC i was talking the actual carbs not the float levels

 

[Large]

Ok, so here are some pics, front, side, back and with the floats in place and what the manual says the height should be. The frame number is 4G6-006721.

 

[HoughMade]

The manual is wrong...at least for modern gas. Those indeed look like BS32s, not 34s that you would normally find on an XS400. They could be made to work with jetting, but personally, I would want the proper carbs. Maybe 'cause I'm lazy. I had enough trouble chasing the proper carb settings with the original carbs.

You are right, "4G6" is the number for an XS250.

 

[drewpy]

you can get them to work, just needs to find the right size jets!

 

[Large]

So would that mean just getting jets the same size as the ones in a 400 carb or because the carbs are smaller and they hold less petrol and allow less air in meaning working out a new jet size to achive the same performance , or am I over thinking the whole thing.

 

[drewpy]

I'd run 'em with what you got and start from there.

I'm sure a guy had the same issue on the Yamaha Owners Club forum!

 

[bcware]

My guess would be that since these carbs are physically smaller you're going to want to increase the total flow through them via pod filters (not emgo) and, obviously, increase the mains and pilots.

 

[Dan]

Hi all & large. I have the same issue. Wondering how you got on.

I have put 125 pilots and 150 mains in my carbs. Ticks over ok. But not riden yet as no brakes. I could be way out and guess I probably am. Hope to,have brakes functioning soon.