carb help

S

stevendefense

torch cut & hammer fit
Started working on my xs 400 some last weekend. Cleaned the tank, set the points, new battery, cleaned and repainted the battery box. and a new tach cable. With my limited knowledge of carbs, I took them to the local bike shop to be cleaned in the ultra sonic cleaner. The guy I talked to there said the vacuum diaphragms have lost their shape and need to be replaced.

Before I took the carbs off I had the bike running for several minutes, but it ran poorly on the left cylinder only. After having the carbs cleaned I put them back on reinstalled the factory air boxes and it ran better, but I still only on the left cyl. After several minutes the right side will pick up and start running. When this happens it smooths out and idles pretty well.

I ran into problems when I tried to ride it. Even after 15-20 of idling it will die instantly if I turn the choke off. Turn it back on and it starts of the first kick. Turn it to half choke and it sputters for a second and then smooths out.

Do you guys think that the diaphragms could be causing this problem? The only place I could find them they come with the slides for $170 each! I would rather not spend that much on the bike right now but I will if I have to. The only other thing that I can think of is that it is running way too lean. When I had the carbs off I turned the mixture screws all the way in, then back out 3 1/2 turns just as a starting for fine tuning later. Could this be my problem?

Thanks in advance for any help you can give me.

-Steven
 
Yeah I had been thinking that same thing. Just a little worried about the condition of the used diaphragms. There are several sets on ebay for cheap. Might not be a bad idea to get a set for spare parts.
 
http://www.mikesxs.net/mikesxs-fuel_system.php?category_id=4.2

Pretty near the bottom of the page on Mike's there's slides for about $60 for the BS34. Don't know for sure if these will fit exactly or not as they're for the 650, but you could check at the Yammy dealership to see if they're interchangable. They're a LOT cheaper than $170 each, and they're genuine Mikuni. I'd send you the slides out of my extra set, but TonUpSoldier has already reserved them for his 400.
 
I looked on a site I found that gives yamaha part numbers and the 400 and 650 parts numbers are different. I should have some time this weekend to work on it so I am going to see if I can richen the mixture and see if that changes anything. I'm still not 100% that the diaphragms are the problem. Having the carbs cleaned made a pretty big difference. I think now I may just need to fine tune them some. If not I found a place close to me that restores carbs, including making new diaphragms so I may call them and see how much they will charge.
 
In the experience that you guys have had is 3 1/2 turns out a good starting point or should I go even further? If so how much?

Thanks
-Steven
 
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