Low RPM Problem
Postmaster
Joined: Jun 2005
Posts: 2,656
Likes: 1
When ever you change the idle speed you need to adjust the mixture screws.... But first check the plates in the primaries look for a slot in the throat right where the plate is making its seal (you need to take the carb off) the plates should be somewhere in the middle of those slots..... If not you need to adjust the secondary plates the opposite way you have to move the primaries to get the plate in the middle of the slots.... those slots are the idle circuits... so if the front plates close off the slots the engine is idling on the rears. You would need to close the rears a little to get the fronts up high enough to get them into the slots
And when you adjust the mixture screws turn them in until the engine starts to stutter...then back them out until the engine smoothes out, do one screw at a time, you may have to go back and forth a few times to get it balanced, bring the idle back down and do it again,. Then I like to back them out 1/8 of a turn and leave it.
If you change the timing, idle speed, plugs, exhaust.... re adjust the carb mixing screws....
Ok I’m done
Hope that helps..... Try pulling the carb and see where the front plates close at......
And when you adjust the mixture screws turn them in until the engine starts to stutter...then back them out until the engine smoothes out, do one screw at a time, you may have to go back and forth a few times to get it balanced, bring the idle back down and do it again,. Then I like to back them out 1/8 of a turn and leave it.
If you change the timing, idle speed, plugs, exhaust.... re adjust the carb mixing screws....
Ok I’m done
Hope that helps..... Try pulling the carb and see where the front plates close at......
Thread Starter
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Junior User
Joined: Sep 2007
Posts: 65
Likes: 0
From: North Shore, L.I. NY
Thank you guys for all of your input. First thing tommorrow morning I am going to dive right at that carb plate. I bought a book ( Holley Rebuilding & Modifying from S-A Design Workbench Books) when I bought the Holley Renew Kit. I think that I followed it to a T, but I very well could have screwed up this plate alignment.
On a side note, there were two power valves in the renew kit: a 25 and a 65. My shop manuals called for the 25. I found advice all over the net, to install the 65. I went with the book and used the 25. What do you guys think about that? In the process I learned a little bit of how a power valve works, and I don't think whichever valve would be affecting my low idle problem.
I hope everyone has been having a merry and a happy
Kenny
On a side note, there were two power valves in the renew kit: a 25 and a 65. My shop manuals called for the 25. I found advice all over the net, to install the 65. I went with the book and used the 25. What do you guys think about that? In the process I learned a little bit of how a power valve works, and I don't think whichever valve would be affecting my low idle problem.
I hope everyone has been having a merry and a happy
Kenny
Last edited by KRH1326; Dec 25, 2007 at 07:26 PM. Reason: word correction
Moderator
Joined: Dec 2001
Posts: 22,436
Likes: 17
From: Louisville,Ky.
The 25 will open at 2.5" of vacuum. This means pretty much only during Wide Open Throttle. The 65 will open @ 6.5" of vacuum. Neither should effect the idle unless they are blown. I'd doubt that it is blown or it would run too rich.
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