Problems idling after carburetor rebuild
Thread Starter
5th Gear
Joined: Mar 2014
Posts: 5
Likes: 0
Problems idling after carburetor rebuild
Rebuilt the carb, it's a rochester quadrajet.
Put it on last night, adjusted the mixture screws 4 turns off.
idle revs up with the fast idle screw completely off (see picture)
There is another screw that is on the side with the choke(automatic [you can see where I set the choke at in the picture]) backed that off alot and it still idles high.
Only other thing that I'm uncertain about when I was putting it together was the screw in the first picture. I didn't tighten it down all the way and it's the only thing I can think of.
Can't really see the smaller throttle plates to see if they're closing completely. It sounds like it when I open and close it it makes that seating noise/feeling. Plus I put it on with the fast idle screw not touching the throttle (as shown in the picture)
Any ideas weather or not this screw that I'm uncertain about (has the rectangular head like the mixture screws) could be the problem?
Much obliged,
JT
Put it on last night, adjusted the mixture screws 4 turns off.
idle revs up with the fast idle screw completely off (see picture)
There is another screw that is on the side with the choke(automatic [you can see where I set the choke at in the picture]) backed that off alot and it still idles high.
Only other thing that I'm uncertain about when I was putting it together was the screw in the first picture. I didn't tighten it down all the way and it's the only thing I can think of.
Can't really see the smaller throttle plates to see if they're closing completely. It sounds like it when I open and close it it makes that seating noise/feeling. Plus I put it on with the fast idle screw not touching the throttle (as shown in the picture)
Any ideas weather or not this screw that I'm uncertain about (has the rectangular head like the mixture screws) could be the problem?
Much obliged,
JT
Melting Slicks
Joined: Jul 2010
Posts: 2,503
Likes: 33
From: McGrady NC
St. Jude Donor '15-'16
Turn the choke thermostat until the choke plate starts to open. It appears that you have the spring tension too tight. Check for vacuum leaks and make sure the throttle plate is not binding against the intake bores.
Burning Brakes
Joined: Mar 2010
Posts: 803
Likes: 4
From: Christchurch, New Zealand
Sounds like you got a vacuum leak.
I can't believe how stupid I was, but somehow, I had left the washers on the two studs, put the carb base gasket on, and tightened her up with new washers to replace the ones I "lost". No matter how much I tightened the carb to the manifold, it wouldn't idle down!
Another thing to check would be your fast idle adjustment.
I can't believe how stupid I was, but somehow, I had left the washers on the two studs, put the carb base gasket on, and tightened her up with new washers to replace the ones I "lost". No matter how much I tightened the carb to the manifold, it wouldn't idle down!
Another thing to check would be your fast idle adjustment.
2026 Loser of the Year
Joined: Sep 2013
Posts: 36,601
Likes: 7,047
From: New Or-leens Loo-z-anna
If the accelerator-pump lever is adjusted too tightly, it will allow fuel will be sucked into the carb causing the engine to idle faster.
LARS is the carb "surgeon"....he could give you good advice.
LARS is the carb "surgeon"....he could give you good advice.
Thread Starter
5th Gear
Joined: Mar 2014
Posts: 5
Likes: 0
It ran fine before rebuild, and I didn't adjust the accelerator-pump lever. Can somebody tell me what that screw that I was refering to (picture 1) next to the accelerator pump is, and if it needs to be adjusted?
Thread Starter
5th Gear
Joined: Mar 2014
Posts: 5
Likes: 0
Also, that picture is sideways, in case you thought it might have been right-side up, in which case I most definitely over-tightened it.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
You can't set the mixture screws before the engine is up to temp and the choke has opened completely. You also want to verify that the throttle plates have closed COMPLETELY when the linkage is brought back by the return spring. If the carb was put in place just a bit off proper location, the plates can hang up on the carb gasket and/or manifold openings. Loosen the 4 mounting bolts, wiggle the carb around to find the best 'center' location, snug the bolts and actuate the throttle while watching the primary throttle plates. They must shut completely with the mounting bolts loose and when you tighten them.
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Safety Car
Joined: Apr 2006
Posts: 4,057
Likes: 421
From: BC
The idle screw is backed right out but the throttle isnt closing as seen in your pic. When you installed the throttle cable did you adjust it for full travel? It looks tight but is way off the idle stop.
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
FYI the fast idle screw is the one on the right hand side of the carb, underneath the choke. The curb (slow) idle screw is the one not touching the throttle in the 2nd pic. You're definitely stuck on fast idle there.
You can hold the choke flap wide-open, as mentioned, and blip the throttle to get it off fast idle. The advice above on relaxing the choke housing to where the choke is *just* closed at cold idle is very good.
Of course, is the choke is not functioning you'll still have a fast idle problem.
You can hold the choke flap wide-open, as mentioned, and blip the throttle to get it off fast idle. The advice above on relaxing the choke housing to where the choke is *just* closed at cold idle is very good.
Of course, is the choke is not functioning you'll still have a fast idle problem.
Melting Slicks
Joined: Mar 2007
Posts: 2,520
Likes: 11
From: Hinckley OH
"The power piston is equipped with a small pin that contacts the APT adjustment screw, which can be adjusted externally. This APT system allows for full control over part-throttle air/fuel ratios by simply repositioning the tapered portion of primary rod in the primary jet."
I don't remember why but I ran into this when I rebuilt my carb. There is no exact spec for setting it but I know that I had to get mine right by trial and error. You can adjust it with the engine running. It could be your problem.
Pro
Joined: Nov 2013
Posts: 730
Likes: 37
From: Catoosa Okla
Looking at your picture, it looks like the choke is holding the fast idle cam closed. The throttle blades dont look closed. This said, my first guess is a massive vacuum leak. What happens if you restrict air into the throat of the carb with your hand? Does it attempt to run closer to an idle?
Melting Slicks
Joined: Jul 2010
Posts: 2,503
Likes: 33
From: McGrady NC
St. Jude Donor '15-'16
If nothing has worked so far:
Take the throttle cable and cruise control link off the carb. Then try to adjust it. Your cable looks tight from the pictures and could be holding the throttle open.
I still say it's the choke adjustment...
Take the throttle cable and cruise control link off the carb. Then try to adjust it. Your cable looks tight from the pictures and could be holding the throttle open.
I still say it's the choke adjustment...
Thread Starter
5th Gear
Joined: Mar 2014
Posts: 5
Likes: 0
Looking at your picture, it looks like the choke is holding the fast idle cam closed. The throttle blades dont look closed. This said, my first guess is a massive vacuum leak. What happens if you restrict air into the throat of the carb with your hand? Does it attempt to run closer to an idle?
Thanks for the help so far guys, I'll keep an update,
JT