Help with detent downshift/ carb settings
Thread Starter
Racer
Joined: Dec 1999
Posts: 278
Likes: 0
From: Gold Coast, Australia
Help with detent downshift/ carb settings
I understand that the correct way to adjust the detent downshift cable is to open the lock tab, open carb to WOT, hold this position and close lock tab.
I seem to get no downshift at speeds over 40mph. It just bogs. If I set the downshift cable to 3/4 WOT then it works fine but then I am sacrificing horsepower.
I thought my problem was due to the secondaries opening too soon so I checked the tension spring and adjusted to 7/8 turn as per factory specs and also adjusted the dapshot to .015 once again as per factory specs but I still have the same problem.
Should I try setting tension spring higher or is there something else I am missing?
Cheers, Guy.
I seem to get no downshift at speeds over 40mph. It just bogs. If I set the downshift cable to 3/4 WOT then it works fine but then I am sacrificing horsepower.
I thought my problem was due to the secondaries opening too soon so I checked the tension spring and adjusted to 7/8 turn as per factory specs and also adjusted the dapshot to .015 once again as per factory specs but I still have the same problem.
Should I try setting tension spring higher or is there something else I am missing?
Cheers, Guy.
Racer
Joined: Sep 2002
Posts: 357
Likes: 0
From: Sayville New York
Re: Help with detent downshift/ carb settings (glenga)
Glenda, I posted a similiar question about the detent cable in my Vette as well, but got no responce. I needed to know how to adjust the cabel. I'm sorry I don't have an answer for you you kind of helped me with your question. So I hope by replying this gets your post up to the top and gets you (and me) some more info.
Burning Brakes
Joined: Jun 2002
Posts: 837
Likes: 3
From: Texas
Re: Help with detent downshift/ carb settings (glenga)
Wow, you guys have really been left out. My earlier model vette downshifts using a detent switch so I'm not speaking from experience here. This info concerning detent cable adjustment comes from the manual. It appears that your method of adjustment is correct......remove snaplock, open carb to full throttle, push snaplock into place. The following is additional info from the book that may be helpful. This is for TH350s 78 thru 81.
" The detent valve is actuated by the downshift detent cable, which is connected to the carburetor linkage. When the throttle is 1/2 open, the detent valve is actuated, causing a part throttle downshift at speeds below 50 mph. When the throttle is opened completely, the detent valve is actuated, causing the transmission to downshift. The 3-1 valve is actuated, causing the transmission to downshift. The 3-1 detent downshift occurs when vehicle speed is approximately 6 to 12 mph below the maximum throttle 1-2 upshift point. The 3-2 detent downshift occurs when vehicle speed is approximately 4 to 8 mph below the maximum throttle 2-3 upshift point."
Hope this helps... if not, you'll at least be back to top and maybe get more advice.
" The detent valve is actuated by the downshift detent cable, which is connected to the carburetor linkage. When the throttle is 1/2 open, the detent valve is actuated, causing a part throttle downshift at speeds below 50 mph. When the throttle is opened completely, the detent valve is actuated, causing the transmission to downshift. The 3-1 valve is actuated, causing the transmission to downshift. The 3-1 detent downshift occurs when vehicle speed is approximately 6 to 12 mph below the maximum throttle 1-2 upshift point. The 3-2 detent downshift occurs when vehicle speed is approximately 4 to 8 mph below the maximum throttle 2-3 upshift point."
Hope this helps... if not, you'll at least be back to top and maybe get more advice.
Thread Starter
Racer
Joined: Dec 1999
Posts: 278
Likes: 0
From: Gold Coast, Australia
Re: Help with detent downshift/ carb settings (glenga)
Goinbroke: Thanks for your reply. I have gone over that same paragragh a few times in the Haynes manual but can't find anything that will help.
Burning Brakes
Joined: Jun 2002
Posts: 837
Likes: 3
From: Texas
Re: Help with detent downshift/ carb settings (glenga)
Glenga, It almost sounds like you need to back off on the spring tension for that top butterfly valve. If the secondaries are opening as they should, the suction (engine vacuum) will pull those top valves open. If the spring tension is too tight they may be unable to open causing the bog that you're experiencing.
I really think you need Lars to step in here and have a go at this one. It's sounding more like a carb problem than a detent problem to me, but I have very little experience when it comes to carbs.....especially Q-jets.
[Modified by goinbroke, 10:38 PM 4/14/2003]
I really think you need Lars to step in here and have a go at this one. It's sounding more like a carb problem than a detent problem to me, but I have very little experience when it comes to carbs.....especially Q-jets.
[Modified by goinbroke, 10:38 PM 4/14/2003]
Thread Starter
Racer
Joined: Dec 1999
Posts: 278
Likes: 0
From: Gold Coast, Australia
Re: Help with detent downshift/ carb settings (glenga)
Gionbroke - Yes you are right. It does sound more like the carb problem than the tranny. If I set the detent cable to work before the secondaries open then it functions correctly. I have the secondary spring tension adjusted to factory specs (7/8 turn) so maybe I need to play with this setting and see if it makes any difference.
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