Carb Adjustment

I decided to pull my carbs yesterday to change my float height. I snapped a few pics and made an album on the pictures page. I thought it might be nice to use them as visual aids.
 
hardtailed77 said:
Awesome! Thanks alot, that is exactly what I needed. I just needed a factory setting to start at, so I can tune from there since I have wide-open pipes and pod filters. The bike runs decent at the moment, but the left cylinder has way more pressure at the end of the exhaust tip than the right side does, until you get into the throttle at all. After that, it seems to be totally fine. So I'm thinking that the right carb is flooding the cylinder until you crack the throttle and the engine burns off all the excess gas. I'm going to tune the carbs and then test out my homemade manometer that I just built, and go from there. Thanks again for the quick reply.
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it's funny ... my 400 sohc same thing happens and I was thinking about the problem of the carburetor float. I start work ...
 
Some of you older gents might remember one of these. It was given to me by a friend that had it in his basement since the 70's works awesome. carb stix mercury gauges for syncing carbs.:D
 
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Stupid question from a newbie here, but is the air screw the same thing as a pilot screw? Planning my first ever carb rebuild and want to do as much research as possible first.
 
One more question, a lot of people on here saying to check with mikesxs.com for carb parts. Are the BS34 parts he offers for the 650 interchangeable with the parts needed for the 400? Exceptions I would assume being the jet and needle sizes? (Stock application). Thanks in advance for any help, really nervous about this one.
 
The 1980-82 sohc xs400 bs34's are mostly the same as the 1980-84 xs650 bs34's
 
Yamaha Newbie said:
Stupid question from a newbie here, but is the air screw the same thing as a pilot screw? Planning my first ever carb rebuild and want to do as much research as possible first.
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there are no air screws on the carbs only air jets.

the pilot screw sets the fuel mix and works the engine up to 4k revs when the mains take over!
 
Thanks xschris, I'll probably have to order the kit from Mikesxs and either add to it or take out as needed once it arrives. Trying to avoid it if at all possible.

Thanks for indulging my ignorance drewpy, and for the tip on the cam covers. So if I have sluggish operation at idle off chock (usually with an engine cut out after a minute or so) and on choke the engine runs away to about 4000, I would assume the carbs need to be cleaned (at least) and adjusted. Except I have pretty heaving carbon on the spark plugs (Lord knows how long ago they were put it), which would point to too rich of a mixture while everything points to too lean a mixture. I'm trying to get the bike on the road (reliably) as cheaply as possible, should I just bite the bullet and get the rebuild kits?
 
The other thing that causes black spark plugs is engine oil- either up through the rings or down through the valve stem seals. I wouldn't worry about that right now, though. Were it me, i wouldn't even mess with trying to adjust the carbs until i knew they were as clean as I could get them.

As for parts, My bike sat for almost 15 years and when i went through the carbs I replaced not a single part. I made float bowl gaskets with gasket paper (easy) but the jets, float, screws, and everything else is original. A good cleaning is usually enough. the jets just need to be cleaned and do not need to be replaced unless physically damages. the same goes for the emulsion tube and float needle. On rare occasions, diaphragms will go bad, but usually not.
 
The older pre 80 carbs have no rubber parts inside of them. The 80-82 carbs do. The pilot jets have a rubber plug over them witch go bad, and a o-ring around the float needle seat as well as the needle its self having a rubber tip. It is a good practice to change these before you start tuning a bike that has sat a while. They do go bad:)
 
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Thanks XS. Per HoughMade's advice I pulled the carbs last night and have them sitting on the workbench waiting for dismantling and cleaning, probably early next week. Since they are off I looked inside the rubber connecting mounts that sit between the carbs and engines. The outsides are cracked pretty much all the way around, but there are NO cracks or holes on the insides, so I'm hoping I can get by without replacing them until I do a full tear down this winter.

XSchris, are those rubber pieces in your pictures available from Mikesxs? Part number? Also do the boots from the 650 work on the 400. Same carbs and diameters from what I can tell. I found a pair of 400 mounts on ebay for like 30 bucks, but I always like to have a back up plan just in case.

Thanks again for the assist guys.

Edit: I think I just found the parts you were talking about XSchris on Mikes Part #48-1408.
 
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The 650 mounts will not work. I would get the ones off ebay, even a small crack can cause issues.
 

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