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 Post subject: Sticking SU Carb
PostPosted: Fri Jun 26, 2020 8:15 am 
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Joined: Sun Jun 16, 2019 10:27 am
Posts: 1
Help: I have a sticking SU carb piston problem. The car has dual carbs and the front carb works well. The back piston stick at the very bottom. it takes significant pressure with your finger to start it moving. Once the piston is free it works as expected. It drops within time and has the distinct ker-plunk sound. I've inspected and cleaned the parts and all appears good to go. Thoughts???
Wondercat Racing


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 Post subject: Re: Sticking SU Carb
PostPosted: Fri Jun 26, 2020 8:21 am 
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Joined: Mon Feb 29, 2016 9:12 am
Posts: 140
Location: Boston, Ma
Needle binding in the jet?
Nick somewhere on the I.D. of the cover?
Messed up damper bore?
Messed up slot for alignment pin?

Take needle out or jet out and see if the problem persists.

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Anthony Parker
NER 373024
E-Prod. Wanna-be


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 Post subject: Re: Sticking SU Carb
PostPosted: Fri Jun 26, 2020 8:24 am 
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Joined: Sun Aug 18, 2002 6:52 pm
Posts: 2226
Location: Topeka, Kansas
The jet isn't centered in the carb body. You can buy a tool for this. Very critical for SU carbs.

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jesseprathermotorsports.com


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 Post subject: Re: Sticking SU Carb
PostPosted: Fri Jun 26, 2020 10:48 am 
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Joined: Wed Jul 06, 2011 3:48 am
Posts: 688
Location: Florida
If you are running ancient history like the rest of us we've found that eventually the chamber bases warp binding with the needle assembly. Solved some problems by mild sanding, turning the chamber 180 degrees, or throwing them away and getting another one out of the huge box of spares we collected over the years. Check jet alignment first as besides binding up the needle it won't meter fuel efficiently. Other than that I'd do anything Jesse suggests. It's good to have that much expertise on board.

Bob

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Bob Hess 165947
HP 13 '59 AH Sprite HP Hybrid
HP 49 '60 AH Sprite HP/Vintage


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 Post subject: Re: Sticking SU Carb
PostPosted: Fri Jun 26, 2020 4:36 pm 
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Joined: Tue Nov 03, 2009 6:44 pm
Posts: 919
The nut at the bottom of the carb body locks the jet in place. The jet can float with a lot of side movement until this is locked down. Loosen it and use the needle in the dashpot to center it. Make sure that the needle moves freely after you tighten up the nut. It might take a couple tries to get it right. Unless there is something strange happening in the dashpot or damper piston that is most likely your problem as has already been stated in previous posts.

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 Post subject: Re: Sticking SU Carb
PostPosted: Sat Jun 27, 2020 7:44 am 
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Joined: Wed Jul 06, 2011 3:48 am
Posts: 688
Location: Florida
Oops... Forgot to add Ron on the expertise list.

Bob

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Bob Hess 165947
HP 13 '59 AH Sprite HP Hybrid
HP 49 '60 AH Sprite HP/Vintage


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