xs400 (sohc) carbs

[ras675]

my second posting , sorry to keep asking questions , hopefully one day I will have the abilities with yamaha,s to answer some?

I have a 1980 xs400 that is an american import (we think) , the bike was bought from the back yard of a dealers , as a customers non runner , after a bit of work doing the fork seals , freeing the brakes , and most importantly getting her to run on 2 pots (fuel vac pipe off!) , she has an mot.

now the bike had been played around with by the PO father , carbs mainly , and i,ve reason to suspect that the floats were swopped , they are the brass type.

can,t seem to locate info on those carbs , but the later DOHC shows that you set them on the fuel hight using an external clear tube mounted in an adaptorfrom the drain plug,

i,m used to doing this , working on old amals (enfields and BSA,s )

I have had an adaptor machined (wierd thread?) and am ready to start , the DOHC book says 3 mm + or - 1mm from the float bowl level , can anyone confirm this setting for the 400 SOHC,

I have done a search on float hights , but in this case I don,t actually know if they are the correct ones ,

many thanks

alan

preston

UK

[Hornix]

hi preston,

My haynes manual says for the XS400 BS34 Mikuni:

32.0 +/- 1mm (1.26+/-0.04 inch).

Hope this helps!

[ras675]

hi preston,

My haynes manual says for the XS400 BS34 Mikuni:

32.0 +/- 1mm (1.26+/-0.04 inch).

Hope this helps!

thanks mate , i found that after a bit of research on this site , also mentioned was the fact that haynes had made a misprint , and it was closer to 28mm

the reason i want to do it the way shown in the book (at least the DOHC book) is that i actually don,t know if those are the correct floats , might be bigger/smaller for all i know , but by using a clear plastic tube , i will know how far it sits below the chamber level

i do appresiate you coming back and answering tho ,

do you know of a link to a manual for a 80 sohc electronic ign bike , the links at the beginning of the forum seem dead

cheers

(ps its alan in sunny preston lancashire UK)

alan

edit:

found this manual

http://www.freeonlinerepairmanual.com/Manuals/Yamaha%20XS360_XS400.pdf

mine seems to be the se model , ie: 16 in rear wheel ,and electronic ig on page 34 , its saying 27.1mm for the se model

just to confirm , my engine is 3f9 14262 , frame id, 3f9

[drewpy]

don't use the haynes manual for the setting, its 26mm tried 32mm and ran crap,took ages to get back to the 26mm setting as i thought it wrong. german website confirmed this and I've posted this before on this forum

[ras675]

well she was mot,ed , then there was an accident , see here http://cgi.ebay.co.uk/1980-YAMAHA-RED-now-free-fire-damage-/170574562029?pt=UK_Motorcycles&hash=item27b70942ed auction almost over , sad to see here go tho ,

[Cy Welch]

At least on the American model for 80 the float height is 27.5mm and the floats are supposed to be brass. There is also supposed to be a plug over the idle jets as they pull fuel through the main jets. If it has the stock carbs, they will be Mikuni BS34 III's, which in the U.S. were shared by many other models in 1980, just with different jets and diaphragm springs. The DOHC bikes have a different bowl on them and your supposed to use the clear tube. AFAIK, there is no spec for the 80 carbs outlining the fuel level using the tubes, only the float height setting.

Also, a common problem on these carbs is for the o-ring on the push in needle valve seat to wear out and let fuel leak around them causing the carbs to overflow, if that was not replaced you might want to do that.