Is this jet set-up right?

The 45 should be fine, but I would get a 145 just to make sure. You might have to change your needle jet position as well to take care of the mid range if you don't know that already.:) Mikesxs.net is a good place as is a yamaha dealer they are selling the same cheaper aftermarket jets too.( at least the one where I live)
 
Neither, the xs400 uses BS34's. I looked at that guide. It's generally right. But the bike they were using is a 4 cylinder bike and a lot bigger than 400 cc's.
This guide is more geared to the XS650 carbs, But the BS34 carbs used on the XS650 are very simular to the BS34's on your XS400. The tuning section is more detailed than the one you linked. It tells how to test the jetting and how to adjust.
www.amckayltd.com/carbguide.pdf
Leo
 
What is your stock main size? Year of bike?

With stock air filters and emgo shorty mufflers I ran 150 mains last summer on my '78. No matter what I would recommend buying a range of main jets along with 1 and 2 sizes up on the pilots if you can.

The jets are cheap, but shipping from mikesxs is expensive to me in NH. Rather than risk having to reorder another size I bought all sizes larger than stock :D
 
You can find genuine Mikuni jets locally at most any place that works on dirt bikes, atv's, snowmobiles, jet ski's. Even dealers.
If you talk to the shops they might have a bunch of gently used jets to choose from. They might let you buy a bunch, buy back the ones you don't use.
Used saves money. Even the new will be about the same as Mike's and save shipping. Look around.
Leo
 
Thanks XSLEO. I went with the 145/45 from mikes at the same time as new levers/petcock, filters/fork seals etc, so shipping was already being paid for. If I have to change jets from there, than I will buy local. Thanks for all the help guys!
 
Ok question about jetting..... I saw someone suggest removing the rubber pilot jet plug. My question is, I am going to run open trumpet exhaust and pod filters, what jetting combo should I use and should that rubber plug really be removed? I am in the High Desert, about 4500 feet so I am thinking 145 main, 45 pilot. Thoughts?
 
I wasn't going to, I just wanted to make that clear to others who may have read that online. It seems like pretty common "advice" online that the plugs should be removed!
 
The only plug that should be removed is the brass one that covers the idle mix screw on the 80-82 sohc xs400's
 
i made some mods to my bike (xs 400E 1978) , got a 2-1 exhaust and got k&n filters, what size of jets and pilots should i get?? the exhaust got smaller mufflers than stock ones .
 
Last edited:
When I jetted for pods and open pipes I used 150 mains and 45 on the pilot.I cant adjust my slide needs unless I find some small washers for shims but it seems to be running very good as it is.Now I have a more restrictive quieter exhaust and haven't changed the jets the bike still seems to run pretty good.
 
Your 78 should have the adjustable needles for the mid range so don't worry about that part.
 
I never changed my needle height :shrug: It seemed to work best at stock height even with a few different pod/exhaust setups now. Maybe it's my climate/elevation.
 

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