What is a good idle?

suntreemcanic

Experienced Member
I have put together a 425 Nailhead and installed it in a 1952 Buick woodie station wagon. The block is a 1966. The intake is a 1963. The heads are 1959. I have the engine running and it was balanced. The cam is a mild version for torque. I bought a new Edelbrock 800 CFM carburetor. It has 150 pounds compression, 18 inches vacuum. With 3:08 reared gears it will spin one tire just by stepping on the gas. I don't know of any Buick Nailheads around here to compare it too. I do not like the way it idles. I have read that Buick cams are pretty aggressive. Does that mean they do not idle smooth? I can screw the idle mixture screws all the way in and the engine continues to run. I have exchanged carburetors and the idle mixture screws act the same. I have removed the intake manifold and inspected it. I have inspected the carburetor gasket to make sure there are no leaks. I have sprayed starter fluid around everywhere and no sign of a leak. Any one have a idea?
 
Are your primary throttle blades closing all of the way at idle once the choke is off? I have had to drill some small holes in the primary blades to improve idle before, but that was with large cams that only produced 9# of vacuum. You have 18# and that is considerable. You are adjusting the screws for best vacuum? Is the vacuum advance plugged and disconnected when you are adjusting the screws? Have you tried it using a ported vacuum source for the vacuum advance? How is the timing? How is you PCV valve?


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Though Edelbrock recommended the steel base plate and a ¾ inch wood insulator all of that has been removed and only a gasket is between the carburetor and the intake manifold. The PVC vacuum port, the transmission vacuum port, the power brake vacuum port have all been disconnected and plugged off. The surface of the intake manifold is in good condition. I have sprayed starter fluid around the base of the carburetor and can not here an idle change. I have taken the intake manifold off and checked the faces of the heads and the faces of the intake manifold where they fit together and they are flat. My timing is set at 12 degrees with vacuum advance plugged. The distributor was rebuilt and mechanical advance all in at 2500 RPM's. The vacuum advance is new. The fuel pressure is 4 ½ PSI. Looking down from the top the primary throttle blades look like they are closed but I do not have long feeler gauges that will reach all the way down there to check for sure.
 
Vern,

A couple things. 1st. the metal plate is a nec. piece that you NEED. Or else it's sucking exhaust into the intake. You ALSO need the correct base gasket. What comes with the carb. is NOT for a stock Buick manifold. It needs the "smiley" face gasket. Gasket on manifold. Metal plate above that to the bottom of the carb.
2nd, the Edelbrock carb. has 2 BIG vacuum ports. one front & one rear. Both for a PCV valve & or a brake booster or one for both IF you have it set up like that which you can do to make things look a little better/neater. IF you remove the carb. & look at the base & look at your manifold you will see that the way the base of the carb. is shaped those ports extend out from the front & rear of the carb. The gasket, EVEN the correct one comes VERY ClOSE to sealing, BUT NOT quite. What you have is a vacuum leak, although small, it is sucking air. Starting fluid, Brakleen or whatever your using to check won't usually pick it up UNLESS you spray directly at the area I'm talking about. Even then though you sprayed it, & has little or no effect I'm almost positive it still HAS A VACUUM LEAK.
Pull the crab. off yet again & check out what I'm talking about. These ports ALMOST seal, but not quite. What I've done before is fill in the port, partially to seal that area with JB Weld or equivlent.
I am sure I am correct as have run into this numerous times.

Tom T.
 
I have to wait till morning to start car (noise) but I think I found the problem. I removed the carburetor and put it on some 4 inch bolts to raise up off shop table. Put a light under the primary bore and looked through top of carburetor down through primary bore and the light shown real bright between primary blades and carburetor walls. I discovered with the choke held wide open that the fast idle adjustment screw was holding the primary throttle blades from closing completely. So I made the adjustment according to manual. Hope this is my problem!
 
Thank you Tom. I will look at all your above points in the morning because my carburetor is off and on the bench. It only takes about 10 minutes to install it. No hood no fenders no grill.
 
My 425 is running much smoother now. I traced it down to the spark plugs. Several of the spark plugs were not firing all the time like 7 out of 10 times which made the engine run ruff and shake a little. They were new plugs and I replaced them with exactly the same. I would like to try it out but winter finally came now there is snow on the road
 
More snow is coming, and my exhaust pipes are about 80% designed then probably a day of welding. Can not wait to try the engine out when it is running on all eight all the time.
 
Ok it was colder than.......but I took her out and ran it. Idles real smooth and my exhaust system is quiet. The engine really revs when I get on it. Those pistons from Tom Telesco (TELRIV) make power. I am going to hook up a temporary tachometer to see what is going on. I have not driven it very fast because The whole front end has been torn down and reassembled only using a square on the floor against the tire and adjusting toe-in by squaring them up with the rear tires. And my Wilwood vacuum boosted disk brakes work great.
 
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