what is this screw

[phatman1969]

I just bought an xs400 and it has carb issues. It does run, but rough. Behind the idle screw, where the throttle cable attaches there is a flathead screw that looks like brass. What does this screw do? It appears to be all the way in but looks like it is an adjustment. I have looked at the other posts but some of the descriptions used are confusing. Any help would be appreciated.

 

[bentwrench]

Year of the bike? Pictures tell a thousand words, too...

 

[phatman1969]

year is 1982, will try to get a pic if i can figure out how to upload it. Basically behind where the throttle cable hooks to the slide arm on the right carb is the flathead screw. thanks

 

[bcware]

It's probably the synch screw, but I would take a photo to be sure.

 

[bentwrench]

Yeah, flat head brass screw on my carb by the throttle is the idle adjustment screw. Odd that it would be all the way in...

 

[tim4891]

just a guess with out a pic but does the other side have the same screw. if it does it could be for the starter jets if the bike is equipped with a enricher rather than a choke

 

[phatman1969]

Thanks for the replies, I cleaned the carbs today and took the screw all the way out.It appears to do nothing. I find it odd to have a brass screw in the side of a carb with no hole behind it! The sync is in the middle between both carbs, the mix screws are on top facing the front. I guess its just a dummy screw. On the other carb there is a metal cap where this screw would be. On a good note did get the bike to run a ton better today. Still working on it.

 

[phatman1969]

Ok, took a pic of the screw just in case I am missing something. Like I said behind it it just looks like a threaded opening with solid metal at the end of it.

 

[phatman1969]

Sorry, it is the slotted brass screw right under the idle arm.

 

[HoughMade]

Looks like the idle air screw to me.

 

[drewpy]

I think its just a stop for the return spring!

 

[corruptmind]

Im with Drewpy, it appears to be holding tension on the spring.

 

[bcware]

If that is your throttle cable attached to that rotating bracket I am going with idle adjustment screw!

 

[bentwrench]

All right, I'm tired of this guessing.

I just checked my carb. The screw doesn't adjust or hold anything. The second carb has a blank in the same spot. When I look it up in the parts manual, it's listed as a Cylinder Head screw (part number 98302-05006).

So basically, don't touch it.

 

[corruptmind]

yeah i looked at my carbs yesterday, right hand side has it, which is the same the throttle attaches to, then the spring to snapping the throttle closed is on that, basicly its like Drewpy said, its there as a spring stop.


let my reword this as i have my carbs in my hand right now. This is for an 81 XS400 Both of my carbs have the screw, both are on the inside when together (Right carb has it on the left, left side carb has it on the right) both hold tension on the spring that snaps the throttle closed, and both also act as a throttle stop. (when you open the throttle all the way the it hits that screw to stop it from opening beyond 90 degress)

 

[bcware]

Interesting and informative. Thank you for doing to leg work guys

 

[phatman1969]

Thanks to all who took the time to really search out the answer for me. I really appreciate it. I did just what you said and left it alone. Hopefully will have time to play around with the electrical today. Thanks again.