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Dan2973
Samba Member
Joined: April 12, 2019
Posts: 434
Location: NJ
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 Posted: Sun Apr 05, 2020 12:55 pm Post subject: 40 hp carb screw |
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Any of you guys out there have a fix for this stripped out screw on the carburetor arm? Was thinking of just using another screw and jamb nut like shown in the photo. What exactly does it do and how does it operate? Thanks guys
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wcfvw69 
Samba Purist
Joined: June 10, 2004
Posts: 13389
Location: Arizona
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| Posted: Sun Apr 05, 2020 1:41 pm Post subject: Re: 40 hp carb screw |
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Reach out to Tim at Volkzbitz.com as he may have a spare arm he can sell you.
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Cusser
Samba Member
Joined: October 02, 2006
Posts: 31362
Location: Hot Arizona
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| Posted: Sun Apr 05, 2020 1:41 pm Post subject: Re: 40 hp carb screw |
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| Dan2973 wrote: |
| Was thinking of just using another screw and jamb nut like shown in the photo. |
Your way would work. So would be tapping to a larger thread size (fine thread) and using a bench grinder to shave down the end of the screw if necessary.
| Dan2973 wrote: |
| What exactly does it do and how does it operate? Thanks guys |
On older model carbs, that screw determines the throttle position, like for the idle speed. The little steps on that cam are for its choke, so that screw is also involved in that.
On newer models, there was a separate idle circuit, so the screw would be for the choke cam only.
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glutamodo
The Android
Joined: July 13, 2004
Posts: 26313
Location: Douglas, WY
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| Posted: Sun Apr 05, 2020 1:43 pm Post subject: Re: 40 hp carb screw |
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The stock screw has a finer thread for more precise adjustment plus a machined end that interfaces with the fast idle cam properly. I'd rather keep it. So if one find a nut with the stock thread pitch and weld it to the arm, that would work, or if you have the right tap, weld in the hole and rethread it.
For me, the best fix is to just replace the throttle arm with another one. I did it on my 28PICT carb, not because of the throttle arm screw threads, but because the hole for the barrel clamp got extremely wallowed out:
That's the sort of potential negative you run into when buying used carbs or parts from them. Fortunately I had accumulated enough such parts that I could find a good arm, The image was obviously taken before I moved the spring over from one arm to the other.
Also, to note, the throttle arms changed the angle of the "flats" where they attach to the carb, I think at the time that the 30PICT-1 changed to incorporate a throttle return spring (same time as the 28PICT-1 got the same change and got renamed as the 28PICT-2) as shown here:
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gt1953
Samba Member
Joined: May 08, 2002
Posts: 13848
Location: White Mountains Arizona
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| Posted: Sun Apr 05, 2020 3:43 pm Post subject: Re: 40 hp carb screw |
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I like the way you think. Yes a replacement arm would be correct and screw for it.
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Dan2973
Samba Member
Joined: April 12, 2019
Posts: 434
Location: NJ
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| Posted: Sun Apr 05, 2020 3:45 pm Post subject: Re: 40 hp carb screw |
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| glutamodo wrote: |
The stock screw has a finer thread for more precise adjustment plus a machined end that interfaces with the fast idle cam properly. I'd rather keep it. So if one find a nut with the stock thread pitch and weld it to the arm, that would work, or if you have the right tap, weld in the hole and rethread it.
For me, the best fix is to just replace the throttle arm with another one. I did it on my 28PICT carb, not because of the throttle arm screw threads, but because the hole for the barrel clamp got extremely wallowed out:
That's the sort of potential negative you run into when buying used carbs or parts from them. Fortunately I had accumulated enough such parts that I could find a good arm, The image was obviously taken before I moved the spring over from one arm to the other.
Also, to note, the throttle arms changed the angle of the "flats" where they attach to the carb, I think at the time that the 30PICT-1 changed to incorporate a throttle return spring (same time as the 28PICT-1 got the same change and got renamed as the 28PICT-2) as shown here:
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Ok gotcha. Thanks. I’m still not understanding it’s function. When I mash the peddle down it slides down the cam to the end and just stays there like in my photo. Is that suppose to be like that? |
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EverettB
Administrator
Joined: April 11, 2000
Posts: 69813
Location: Phoenix Metro
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| Posted: Sun Apr 05, 2020 4:29 pm Post subject: Re: 40 hp carb screw |
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| Dan2973 wrote: |
| Ok gotcha. Thanks. I’m still not understanding it’s function. When I mash the peddle down it slides down the cam to the end and just stays there like in my photo. Is that suppose to be like that? |
Yes, this is normal when the choke is cold and closed.
As the choke warms up, the plate rotates and slow opens all the way until the idle screw is resting on the very bottom stop.
This normally takes about 3 minutes or so.
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Eric&Barb
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Dan2973
Samba Member
Joined: April 12, 2019
Posts: 434
Location: NJ
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| Posted: Mon Apr 06, 2020 4:10 am Post subject: Re: 40 hp carb screw |
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| Excellent. Thank you guys. I will read that today |
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