575 Speed Demon Trottle Return Problem
Racer
Joined: May 2005
Posts: 470
Likes: 1
From: Amelia Ohio
I have a new 770 Holley Avenger that started to does the same thing after it was on for about a month. The thing is if I push on the linkage the idle drops off and the engine dies. But where the idle is at 800 the idle still responds when I adjust the screw. Then there is times after I've been driving and shut it off, when I start the engine it won't hold an idle and dies.
It's odd and annoying.
It's odd and annoying.
Thread Starter
Pro
Joined: Sep 2004
Posts: 611
Likes: 0
From: Minnesota
Originally Posted by Doug S
Does the engine return to the lower idle speed if you shut the car off, and restart it, or only if you snap the throttle?
Any idea's?
Le Mans Master
Joined: May 2003
Posts: 8,877
Likes: 3,556
From: Fernandina Beach FL
2023 Restomod of the Year finalist
2020 C3 of the Year Winner - Modified
I also have a 575 mech Speed Demon- I had the exact same problem w/ the carb out of the box.
The throttle was not smooth-the choke was causing it to bind up the last part of the return. I found the problem-there is almost a ¼" of movement on the throttle plate shaft. Needless to say-this makes a big difference on where the throttle plates stop. As it moves in, the stop slides over. See attached pics
I made a spacer and since -carb has worked fine (year and ½)
The throttle was not smooth-the choke was causing it to bind up the last part of the return. I found the problem-there is almost a ¼" of movement on the throttle plate shaft. Needless to say-this makes a big difference on where the throttle plates stop. As it moves in, the stop slides over. See attached pics
I made a spacer and since -carb has worked fine (year and ½)
Thread Starter
Pro
Joined: Sep 2004
Posts: 611
Likes: 0
From: Minnesota
I will have to look at this. I'm not using a choke, so I'm not sure if this is my issue. Also the throttle seems to return fine with the engine off. It also seems to return once the engine is turned off and started again, until you use the throttle again.
Thread Starter
Pro
Joined: Sep 2004
Posts: 611
Likes: 0
From: Minnesota
Originally Posted by Richard454
I also have a 575 mech Speed Demon- I had the exact same problem w/ the carb out of the box.
The throttle was not smooth-the choke was causing it to bind up the last part of the return. I found the problem-there is almost a ¼" of movement on the throttle plate shaft. Needless to say-this makes a big difference on where the throttle plates stop. As it moves in, the stop slides over. See attached pics
I made a spacer and since -carb has worked fine (year and ½)
The throttle was not smooth-the choke was causing it to bind up the last part of the return. I found the problem-there is almost a ¼" of movement on the throttle plate shaft. Needless to say-this makes a big difference on where the throttle plates stop. As it moves in, the stop slides over. See attached pics
I made a spacer and since -carb has worked fine (year and ½)
Thread Starter
Pro
Joined: Sep 2004
Posts: 611
Likes: 0
From: Minnesota
Originally Posted by Doug S
Does the engine return to the lower idle speed if you shut the car off, and restart it, or only if you snap the throttle?
Wondering if you know of a solution to my carb problem.
Thanks
Racer
Joined: Sep 2006
Posts: 484
Likes: 0
From: McComb Ms.
i have a 650 speed demon brand new same thing, a little higher rev at times.Hit the pedal and it'll drop. I've got my dual spring setup in place but for my firm pedal i drilled a hole in my linkage plate and put my linkage closer to the edge to give more leverage, works great! if you drill a hole hold the linkage firmly in place because when the bit drills through initially and bites on the last little piece of metal to be drilled out it could slam your throttle open. I had someone hold mine from that with a round piece of firewood
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Verdad Gallardo
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
If the throttles jam partially open at idle with the engine running, and then close after shutdown, you have a problem with throttle blade alignment in the throttle bores - engine vacuum at idle deflects the blades sightly and can ****/jam them slighty. If I set up your carb, I did test run it and did not have the problem, but you may be pulling more vacuum than I did on the test engine. The solution is pretty simple: Use a long allen wrench (engine not running) and loosen the screws on the throttle blades about 1/4 turn. Back your idle speed screw all the way out and make sure you're not on the fast idle cam. This will fully close the throttles. Now, take a long screwdriver and tap the blades while very slightly wiggling the throttle lever. This will center the blades in the throttle bores. Once the blades are centered after tapping them and wiggling, snug them back up. Re-set your idle speed screw and try it out.
Le Mans Master
Joined: Apr 2000
Posts: 5,202
Likes: 10
From: cincinnati ohio
St. Jude Donor '09
Originally Posted by lars
The solution is pretty simple: Use a long allen wrench (engine not running) and loosen the screws on the throttle blades about 1/4 turn. Back your idle speed screw all the way out and make sure you're not on the fast idle cam. This will fully close the throttles. Now, take a long screwdriver and tap the blades while very slightly wiggling the throttle lever. This will center the blades in the throttle bores. Once the blades are centered after tapping them and wiggling, snug them back up. Re-set your idle speed screw and try it out.
In my case it turns out that the throttle blades are closed so far that the engine vacuum is pulling them open ever so slightly, just enough to increase the idle 100-200 rpm. My only fix is to use more return spring pull
Last edited by yellow 72; Oct 10, 2006 at 05:31 PM.
Thread Starter
Pro
Joined: Sep 2004
Posts: 611
Likes: 0
From: Minnesota
Originally Posted by lars
If the throttles jam partially open at idle with the engine running, and then close after shutdown, you have a problem with throttle blade alignment in the throttle bores - engine vacuum at idle deflects the blades sightly and can ****/jam them slighty. If I set up your carb, I did test run it and did not have the problem, but you may be pulling more vacuum than I did on the test engine. The solution is pretty simple: Use a long allen wrench (engine not running) and loosen the screws on the throttle blades about 1/4 turn. Back your idle speed screw all the way out and make sure you're not on the fast idle cam. This will fully close the throttles. Now, take a long screwdriver and tap the blades while very slightly wiggling the throttle lever. This will center the blades in the throttle bores. Once the blades are centered after tapping them and wiggling, snug them back up. Re-set your idle speed screw and try it out.
Thanks
