Broken Idle Pin?

[Ches]

Hi Guys I was wondering if anyone could help me.

 

I have been trying to tune my 1/8 buggy (Maverick Stealth XB) as it idles at incredibly high revs. However much i turn my idle screw it doesn't open or close the slider in the carb. To compensate I have adjusted my throttle servos but this is only a temporary solution as I still need to make small adjustments. I have taken the screw all the way out to see if it is threaded or broken and all seems well. Is there anything else I should be looking for? Could it be an issue with the carb itself or the housing?

 

If so please could anyone advise how to take a slide carb apart for general maintenance.

 

Any help is appreciated

 

Thanks

[Smoothybb]

The idle screw is only a stopper. The actual action is provided by the servo and linkage. If you screw out the idle screw the servo will still hold the slide in the same position. You'll need to adjust the slide with the trim on the tx. If you screw the idel screw a fair bit out then use the tx to brake, you'll see it will totally close the slide. Screw the idle screw back in a bit and you'll see that even when you brake on the tx, the slide won't close fully. If I understand your problem correctly.

[Ches]

The idle screw is only a stopper. The actual action is provided by the servo and linkage. If you screw out the idle screw the servo will still hold the slide in the same position. You'll need to adjust the slide with the trim on the tx. If you screw the idel screw a fair bit out then use the tx to brake, you'll see it will totally close the slide. Screw the idle screw back in a bit and you'll see that even when you brake on the tx, the slide won't close fully. If I understand your problem correctly.

 

OK I understand better now The only thing is that when i screw in the idle fully and apply the break (this was prior to putting my break linkage in the correct position) the slide still closed fully, stalling the engine. So the screw still allowed this to close. What do you think would cause this problem?

 

So a different but not unrelated question; when people show videos of them loosening and/or tightening their idle screw which allows their carb slider to move, this is because their servo and linkage is set to so the slider is 'pushing' against the stopper? In other words, the linkage/springs should be as tight as possible?

 

Thanks very much for your help I really appreciate it, I'm still new but love to learn!

[Smoothybb]

Sounds like the idle screw is too short then. With it screwed fully in, there's no way the slide should close all the way. (Just remember to always adjust with the slide open so there's no resistance on the screw). You can bring the idle down with the trim adjustment on the tx but then like you say, every time you brake, it'll close completely and stall.

Depending on what tx you're using, in theory you could adjust the end point so that the servo can't move far enough to close the slider all the way. Like a virtual idle screw if you like.

 

"So a different but not unrelated question; when people show videos of them loosening and/or tightening their idle screw which allows their carb slider to move, this is because their servo and linkage is set to so the slider is 'pushing' against the stopper? In other words, the linkage/springs should be as tight as possible?"

 

Yes, the ideal is that at full brake, the slider should push against the idle screw without stressing the linkage or servo too much. Same the other way, at full throttle the slide should be fully open but not still trying to open more or it will stress the servo and linkage.

[Ches]

(Just remember to always adjust with the slide open so there's no resistance on the screw).

 

Maybe I will try that then, I didn't know how is best to adjust and have been adjusting with the carb closed. Perhaps it has just slipped.

 

 

Depending on what tx you're using, in theory you could adjust the end point so that the servo can't move far enough to close the slider all the way. Like a virtual idle screw if you like.

 

 

I think I understand this and have done this to an extent. I did wonder if this is a sufficient way to adjust the idle without the screw and whether or not this would put a lot of pressure on the servo.

 

 

"So a different but not unrelated question; when people show videos of them loosening and/or tightening their idle screw which allows their carb slider to move, this is because their servo and linkage is set to so the slider is 'pushing' against the stopper? In other words, the linkage/springs should be as tight as possible?"

 

Yes, the ideal is that at full brake, the slider should push against the idle screw without stressing the linkage or servo too much. Same the other way, at full throttle the slide should be fully open but not still trying to open more or it will stress the servo and linkage.

 

So in short you want the slider to open fully and close (to the 1mm gap) with the least amount of movement either way? 

 

 

Thank you so much for your help

[Smoothybb]

So in short you want the slider to open fully and close (to the 1mm gap) with the least amount of movement either way? 

 

 

 

Thank you so much for your help

 

 

 

Yeah, the more it tries to open/close beyond the limits of the slider/carb, the more stress you add to the linkage and servo. No problem, it can be frustrating/confusing to start with but once you've done one, it's similar with all others. 

[Ches]

Sweet Can't wait to go give it a go!

 

Thanks for your help again!

[ExLimeyBasher]

Most slide carbs use the same type of idle screw, the screw should have a plain non threaded spigot on the end, this spigot locates in the slot on the slide and prevents the slide from rotating,  screwing the idle screw in or out moves the end positions of the slide, usually the screw is used to obtain the closed position idle gap of 1mm, and the fully open position is controlled by the end point adjustment of the throttle on the transmitter. Maybe your spigot has broke