XS400 Throttle play


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Hi all,

First post here . Looking forward to sticking around. So I recently purchased a well-maintained 1981 xs400 from my friend. It has undergone safety certification and I've hit the road a few times now. While in neutral though, I noticed while turning the handlebars to the far right, the engine revs.

I've been told that the throttle play is too tight and while testing the theory, yes, it doesn't have any play. Zero. So I looked around online (here too) and found that there's an adjustment for cable slack that sits just below the throttle. After a while I was able to unwind it to the furthest setting (see attached), but the throttle still doesn't have any play!

I noticed that on some other bikes, there's another adjustment setting that can be made closer to the motor, but I'm wondering if there is one on the xs400? If so, I'll probably have to take off the fuel tank to access it. If not, I'm not sure where to go from here? I thought these cables were supposed to expand over time. This one looks like was always tightly wound.


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Underneath and between the 2 carbs there should be a thumbscrew. That is where you adjust the rpm. The adjustment on the handlebars is where you take up the free play of the cable.
You should be able to download the service manual from "The Garage" on this forum. This will give you the correct procedure for any adjustments.
The free play is the only adjustment I was looking to make here, since the engine is only revving while turning the wheel to the right side.
How does the thumbscrew to adjust the rpm affect the free play? I thought that one was for the idling rpm.
If you raise or lower the rpm with the thumb screw it will change the position of the butterfly plates(or valves it depends what you want to call them) the throttle cable is connected to the butterfly plates/valves hence changing the resting position of the arm that butterfly's and the throttle cable is connected to.Creating more slack (if you increase the rpm) or decreasing slack(if you decrease rpm).
Thanks for the explanation! So I started the bike up today with the throttle play adjustor in the position I posted (pic above) and the bike was idling up to 4k RPM! I'll have to look at the manual to understand how these two components work in conjunction. Thank-you for the explanation!
I had this same issue and ended up finding that it was caused by the throttle cable getting pinched in the cable bracket right at the front of the frame under the gas tank (it holds the throttle cable and the big cable going to the headlight on mine). I just bent it out a bit so the cable had more space to move around, no adjustments needed.
Take a look at where the cable housing sits at the carb end, if the whole housing gets tugged when you turn the bars all the way (as opposed to just the inside of the cable being pulled) then it's probably the same issue
Thanks guys. I'll check the cable routing later today and report back. I'm currently out on a ride with a friend and don't wanna mess anything up.
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@futureproof - Thanks for following up with a conclusion to the issue. Far too many threads end with lots of recommendations, but no resolution of what did and did not work by the OP. I am glad you got it sorted out!