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Stripped idle set screw

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21 Feb 2022 13:36 #862693 by Dan77kz750
Stripped idle set screw was created by Dan77kz750
Hey everyone. I have a 1977 750 twin. I'm running the stock carbs. When doing some spring maintenence today i found my idle set screw loose, under closer examination the threads in the carb body are stripped out. Kinda explains the wandering idle from right before winter shutdown. 

Looking for suggestions on how to fix this. 

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  • Scirocco
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21 Feb 2022 15:46 #862697 by Scirocco
Replied by Scirocco on topic Stripped idle set screw
Any pics of the carb body and/or stripped threads would help?

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21 Feb 2022 20:23 #862717 by TexasKZ
Replied by TexasKZ on topic Stripped idle set screw
Is your question about the idle speed screw or the low speed mixture screw?

1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

www.kzrider.com/11-projects/620336-anoth...uild-thread?start=24

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21 Feb 2022 21:11 #862724 by Dan77kz750
Replied by Dan77kz750 on topic Stripped idle set screw
I'm talking about the idle speed screw, I will try to get pics of the situation in the morning 

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22 Feb 2022 02:21 #862733 by Dan77kz750
Replied by Dan77kz750 on topic Stripped idle set screw
Here are some pictures of the problem I'm having. The first few are the carb on the bike, the last couple are a parts carb I have extra (cracked body of course) so I could shoe the part from multiple angles.

 

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22 Feb 2022 05:28 #862736 by calum
Replied by calum on topic Stripped idle set screw
I'd just put a helicoil in there. Match the thread if possible, if not just use the finest thread you can find that will fit the hole and then just use a JIS or socket cap screw - looks like it would still be easy enough to adjust.

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  • Scirocco
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22 Feb 2022 13:20 #862769 by Scirocco
Replied by Scirocco on topic Stripped idle set screw
The idle set screw thread looks like be long enough for some flat M5 nuts to adjust and set your idle speed.

 

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22 Feb 2022 15:29 #862777 by Dan77kz750
Replied by Dan77kz750 on topic Stripped idle set screw
The helicoil seems like it would be the better choice as I want to be able to easily adjust this in the future without needing to grab wrenches etc to hold the nuts. 

Now that said, I've never used a helicoil before. I know how they get installed and I'm not intimidated by the thought of drilling tapping etc. Once this is installed will I be able to adjust the screw in and out as needed without the helicoil moving or needing reset? 

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  • Scirocco
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22 Feb 2022 16:05 #862779 by Scirocco
Replied by Scirocco on topic Stripped idle set screw
A Helicoil need a min.1,00 mm over bore size. You will be weaknesses the carb body, trust me.
You don´t need any wrenches, the spring preload do the job. So give it a try before shit happens. 

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22 Feb 2022 21:50 #862788 by calum
Replied by calum on topic Stripped idle set screw
I agree you would take a bit of metal off with the helicoil, but an M5 helicoil needs a 5.2mm drill bit and the tap has a 6.1mm major diameter. That means you'd pretty much be tapping the hole as is and the wall thickness will be reduced by 0.1 - 0.6mm after tapping. That should still leave you with a decent amount of aluminium around the tap, especially given that the load is pretty much all axial. I'm assuming that is an M5 screw and not M4 - hard to tell ifrom the photo.

Having said that Sciroccos way is a safer bet - always better to avoid removing metal if you don't need to. I'd still be putting a helicoil in there just to make my life easier though :)

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23 Feb 2022 12:26 #862824 by Dan77kz750
Replied by Dan77kz750 on topic Stripped idle set screw
Just wanted to update now that I have it fixed. 

I used Sciroccos idea about just using nuts to fix this. The spring load works perfectly fine to adjust the idle, no need for wrenches at all. 

The size of the nut used was M5 x .50 took longer to source the nut than it did to fix the issue. 

My bike now holds a steady idle. Thanks everyone. 

 
The following user(s) said Thank You: calum

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  • Scirocco
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23 Feb 2022 14:45 #862831 by Scirocco
Replied by Scirocco on topic Stripped idle set screw
Good to hear that this simple solution do fix your carb idle setting.

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